26 files changed, 258 insertions, 160 deletions

diff --git a/src/firecfg/firecfg.config b/src/firecfg/firecfg.config
index 05c5681d5..0574daae6 100644
--- a/src/firecfg/firecfg.config
+++ b/src/firecfg/firecfg.config
@@ -327,6 +327,9 @@ gradio
 gramps
 gravity-beams-and-evaporating-stars
 gthumb
+gtk-youtube-viewer
+gtk2-youtube-viewer
+gtk3-youtube-viewer
 guayadeque
 gucharmap
 gummi
@@ -816,6 +819,7 @@ xviewer
 yandex-browser
 yelp
 youtube-dl
+youtube-viewer
 zaproxy
 zart
 zathura
diff --git a/src/firejail/arp.c b/src/firejail/arp.c
index 3714af9a3..f88d0a1dd 100644
--- a/src/firejail/arp.c
+++ b/src/firejail/arp.c
@@ -239,9 +239,7 @@ int arp_check(const char *dev, uint32_t destaddr) {
                 }
         }
 
-        // it will never get here!
-        close(sock);
-        return -1;
+        __builtin_unreachable();
 }
 
 // assign a random IP address and check it
diff --git a/src/firejail/bandwidth.c b/src/firejail/bandwidth.c
index edef823fd..6fd0b53ef 100644
--- a/src/firejail/bandwidth.c
+++ b/src/firejail/bandwidth.c
@@ -327,6 +327,15 @@ void bandwidth_pid(pid_t pid, const char *command, const char *dev, int down, in
                                 devname = strdup(buf + len + 1);
                                 if (!devname)
                                         errExit("strdup");
+                                // double-check device name
+                                size_t i;
+                                for (i = 0; devname[i]; i++) {
+                                        if (isalnum((unsigned char) devname[i]) == 0 &&
+                                            devname[i] != '-') {
+                                                fprintf(stderr, "Error: name of network device is invalid\n");
+                                                exit(1);
+                                        }
+                                }
                                 // check device in namespace
                                 if (if_nametoindex(devname) == 0) {
                                         fprintf(stderr, "Error: cannot find network device %s\n", devname);
@@ -354,6 +363,7 @@ void bandwidth_pid(pid_t pid, const char *command, const char *dev, int down, in
                 }
                 bandwidth_remove(pid, devname);
         }
+        else assert(strcmp(command, "status") == 0);
 
         // build fshaper.sh command
         char *cmd = NULL;
@@ -375,26 +385,16 @@ void bandwidth_pid(pid_t pid, const char *command, const char *dev, int down, in
         }
         assert(cmd);
 
-        // wipe out environment variables
-        environ = NULL;
-
         //************************
         // build command
         //************************
-        // elevate privileges
-        if (setreuid(0, 0))
-                errExit("setreuid");
-        if (setregid(0, 0))
-                errExit("setregid");
-
         char *arg[4];
         arg[0] = "/bin/sh";
         arg[1] = "-c";
         arg[2] = cmd;
         arg[3] = NULL;
         clearenv();
-        execvp(arg[0], arg);
+        sbox_exec_v(SBOX_ROOT | SBOX_CAPS_NETWORK | SBOX_SECCOMP, arg);
 
-        // it will never get here
-        errExit("execvp");
+        // it will never get here!!
 }
diff --git a/src/firejail/checkcfg.c b/src/firejail/checkcfg.c
index 5d6b4af66..f6b3b3252 100644
--- a/src/firejail/checkcfg.c
+++ b/src/firejail/checkcfg.c
@@ -229,6 +229,8 @@ int checkcfg(int val) {
 #ifdef HAVE_SECCOMP
                                 if (strcmp(ptr + 21, "kill") == 0)
                                         cfg_val[CFG_SECCOMP_ERROR_ACTION] = SECCOMP_RET_KILL;
+                                else if (strcmp(ptr + 21, "log") == 0)
+                                        cfg_val[CFG_SECCOMP_ERROR_ACTION] = SECCOMP_RET_LOG;
                                 else {
                                         cfg_val[CFG_SECCOMP_ERROR_ACTION] = errno_find_name(ptr + 21);
                                         if (cfg_val[CFG_SECCOMP_ERROR_ACTION] == -1)
diff --git a/src/firejail/chroot.c b/src/firejail/chroot.c
index cae52e20b..5fc6c8298 100644
--- a/src/firejail/chroot.c
+++ b/src/firejail/chroot.c
@@ -165,7 +165,8 @@ void fs_chroot(const char *rootdir) {
         close(fd);
 
         // x11
-        if (getenv("FIREJAIL_X11")) {
+        // if users want this mount, they should set FIREJAIL_CHROOT_X11
+        if (getenv("FIREJAIL_X11") || getenv("FIREJAIL_CHROOT_X11")) {
                 if (arg_debug)
                         printf("Mounting /tmp/.X11-unix on chroot /tmp/.X11-unix\n");
                 check_subdir(parentfd, "tmp/.X11-unix", 0);
diff --git a/src/firejail/firejail.h b/src/firejail/firejail.h
index 54a1023ab..49d19e33d 100644
--- a/src/firejail/firejail.h
+++ b/src/firejail/firejail.h
@@ -186,7 +186,7 @@ typedef struct config_t {
         char *seccomp_list_drop, *seccomp_list_drop32;  // seccomp drop list
         char *seccomp_list_keep, *seccomp_list_keep32;  // seccomp keep list
         char *protocol;                 // protocol list
-        char *seccomp_error_action;                     // error action: kill or errno
+        char *seccomp_error_action;                     // error action: kill, log or errno
 
         // rlimits
         long long unsigned rlimit_cpu;
@@ -371,14 +371,14 @@ char *guess_shell(void);
 
 // sandbox.c
 int sandbox(void* sandbox_arg);
-void start_application(int no_sandbox, FILE *fp);
+void start_application(int no_sandbox, FILE *fp) __attribute__((noreturn));
 void set_apparmor(void);
 
 // network_main.c
 void net_configure_sandbox_ip(Bridge *br);
 void net_configure_veth_pair(Bridge *br, const char *ifname, pid_t child);
 void net_check_cfg(void);
-void net_dns_print(pid_t pid);
+void net_dns_print(pid_t pid) __attribute__((noreturn));
 void network_main(pid_t child);
 void net_print(pid_t pid);
 
@@ -453,13 +453,12 @@ void profile_add_ignore(const char *str);
 void list(void);
 void tree(void);
 void top(void);
-void netstats(void);
 
 // usage.c
 void usage(void);
 
 // join.c
-void join(pid_t pid, int argc, char **argv, int index);
+void join(pid_t pid, int argc, char **argv, int index) __attribute__((noreturn));
 bool is_ready_for_join(const pid_t pid);
 void check_join_permission(pid_t pid);
 pid_t switch_to_child(pid_t pid);
@@ -486,7 +485,7 @@ int macro_id(const char *name);
 
 
 // util.c
-void errLogExit(char* fmt, ...);
+void errLogExit(char* fmt, ...) __attribute__((noreturn));
 void fwarning(char* fmt, ...);
 void fmessage(char* fmt, ...);
 void drop_privs(int nogroups);
@@ -584,7 +583,7 @@ int seccomp_load(const char *fname);
 int seccomp_filter_drop(bool native);
 int seccomp_filter_keep(bool native);
 int seccomp_filter_mdwx(bool native);
-void seccomp_print_filter(pid_t pid);
+void seccomp_print_filter(pid_t pid) __attribute__((noreturn));
 
 // caps.c
 void seccomp_load_file_list(void);
@@ -595,7 +594,7 @@ void caps_set(uint64_t caps);
 void caps_check_list(const char *clist, void (*callback)(int));
 void caps_drop_list(const char *clist);
 void caps_keep_list(const char *clist);
-void caps_print_filter(pid_t pid);
+void caps_print_filter(pid_t pid) __attribute__((noreturn));
 void caps_drop_dac_override(void);
 
 // fs_trace.c
@@ -618,7 +617,7 @@ void read_cpu_list(const char *str);
 void set_cpu_affinity(void);
 void load_cpu(const char *fname);
 void save_cpu(void);
-void cpu_print_filter(pid_t pid);
+void cpu_print_filter(pid_t pid) __attribute__((noreturn));
 
 // cgroup.c
 void save_cgroup(void);
@@ -640,7 +639,7 @@ void netns(const char *nsname);
 void netns_mounts(const char *nsname);
 
 // bandwidth.c
-void bandwidth_pid(pid_t pid, const char *command, const char *dev, int down, int up);
+void bandwidth_pid(pid_t pid, const char *command, const char *dev, int down, int up) __attribute__((noreturn));
 void network_set_run_file(pid_t pid);
 
 // fs_etc.c
@@ -650,7 +649,7 @@ void fs_private_dir_list(const char *private_dir, const char *private_run_dir, c
 // no_sandbox.c
 int check_namespace_virt(void);
 int check_kernel_procs(void);
-void run_no_sandbox(int argc, char **argv);
+void run_no_sandbox(int argc, char **argv) __attribute__((noreturn));
 
 #define MAX_ENVS 256                    // some sane maximum number of environment variables
 #define MAX_ENV_LEN (PATH_MAX + 32)     // FOOBAR=SOME_PATH
@@ -681,7 +680,7 @@ void fs_private_lib(void);
 // protocol.c
 void protocol_filter_save(void);
 void protocol_filter_load(const char *fname);
-void protocol_print_filter(pid_t pid);
+void protocol_print_filter(pid_t pid) __attribute__((noreturn));
 
 // restrict_users.c
 void restrict_users(void);
@@ -693,7 +692,7 @@ void fs_logger2int(const char *msg1, int d);
 void fs_logger3(const char *msg1, const char *msg2, const char *msg3);
 void fs_logger_print(void);
 void fs_logger_change_owner(void);
-void fs_logger_print_log(pid_t pid);
+void fs_logger_print_log(pid_t pid) __attribute__((noreturn));
 
 // run_symlink.c
 void run_symlink(int argc, char **argv, int run_as_is);
@@ -719,21 +718,24 @@ void fs_mkfile(const char *name);
 
 void fs_x11(void);
 int x11_display(void);
-void x11_start(int argc, char **argv);
-void x11_start_xpra(int argc, char **argv);
-void x11_start_xephyr(int argc, char **argv);
+void x11_start(int argc, char **argv) __attribute__((noreturn));
+void x11_start_xpra(int argc, char **argv) __attribute__((noreturn));
+void x11_start_xephyr(int argc, char **argv) __attribute__((noreturn));
 void x11_block(void);
-void x11_start_xvfb(int argc, char **argv);
+void x11_start_xvfb(int argc, char **argv) __attribute__((noreturn));
 void x11_xorg(void);
 
 // ls.c
 enum {
         SANDBOX_FS_LS = 0,
+        SANDBOX_FS_CAT,
         SANDBOX_FS_GET,
         SANDBOX_FS_PUT,
         SANDBOX_FS_MAX // this should always be the last entry
 };
-void sandboxfs(int op, pid_t pid, const char *path1, const char *path2);
+void ls(const char *path);
+void cat(const char *path);
+void sandboxfs(int op, pid_t pid, const char *path1, const char *path2) __attribute__((noreturn));
 
 // checkcfg.c
 #define DEFAULT_ARP_PROBES 2
@@ -839,7 +841,7 @@ void build_appimage_cmdline(char **command_line, char **window_title, int argc,
 // run sbox
 int sbox_run(unsigned filter, int num, ...);
 int sbox_run_v(unsigned filter, char * const arg[]);
-void sbox_exec_v(unsigned filter, char * const arg[]);
+void sbox_exec_v(unsigned filter, char * const arg[]) __attribute__((noreturn));
 
 // run_files.c
 void delete_run_files(pid_t pid);
diff --git a/src/firejail/fs_dev.c b/src/firejail/fs_dev.c
index fbce72429..00edc5f88 100644
--- a/src/firejail/fs_dev.c
+++ b/src/firejail/fs_dev.c
@@ -25,6 +25,7 @@
 #include <dirent.h>
 #include <fcntl.h>
 #include <pwd.h>
+#include <errno.h>
 #ifndef _BSD_SOURCE
 #define _BSD_SOURCE
 #endif
@@ -148,7 +149,7 @@ static void create_char_dev(const char *path, mode_t mode, int major, int minor)
         return;
 
 errexit:
-        fprintf(stderr, "Error: cannot create %s device\n", path);
+        fprintf(stderr, "Error: cannot create %s device: %s\n", path, strerror(errno));
         exit(1);
 }
 
diff --git a/src/firejail/join.c b/src/firejail/join.c
index 4c8555f29..f202d1a9c 100644
--- a/src/firejail/join.c
+++ b/src/firejail/join.c
@@ -588,7 +588,7 @@ void join(pid_t pid, int argc, char **argv, int index) {
 
                 start_application(0, NULL);
 
-                // it will never get here!!!
+                __builtin_unreachable();
         }
         EUID_USER();
 
diff --git a/src/firejail/ls.c b/src/firejail/ls.c
index aa33d838b..4d0a001b6 100644
--- a/src/firejail/ls.c
+++ b/src/firejail/ls.c
@@ -34,18 +34,12 @@
 static uid_t c_uid = 0;
 static char *c_uid_name = NULL;
 
-static void print_file_or_dir(const char *path, const char *fname, int separator) {
+static void print_file_or_dir(const char *path, const char *fname) {
         assert(fname);
 
         char *name;
-        if (separator) {
-                if (asprintf(&name, "%s/%s", path, fname) == -1)
-                        errExit("asprintf");
-        }
-        else {
-                if (asprintf(&name, "%s%s", path, fname) == -1)
-                        errExit("asprintf");
-        }
+        if (asprintf(&name, "%s/%s", path, fname) == -1)
+                errExit("asprintf");
 
         struct stat s;
         if (stat(name, &s) == -1) {
@@ -178,13 +172,81 @@ static void print_directory(const char *path) {
                         errExit("scandir");
         else {
                 for (i = 0; i < n; i++) {
-                        print_file_or_dir(path, namelist[i]->d_name, 0);
+                        print_file_or_dir(path, namelist[i]->d_name);
                         free(namelist[i]);
                 }
         }
         free(namelist);
 }
 
+void ls(const char *path) {
+        EUID_ASSERT();
+        assert(path);
+
+        char *rp = realpath(path, NULL);
+        if (!rp || access(rp, R_OK) == -1) {
+                fprintf(stderr, "Error: cannot access %s\n", path);
+                exit(1);
+        }
+        if (arg_debug)
+                printf("ls %s\n", rp);
+
+        // list directory contents
+        struct stat s;
+        if (stat(rp, &s) == -1) {
+                fprintf(stderr, "Error: cannot access %s\n", rp);
+                exit(1);
+        }
+        if (S_ISDIR(s.st_mode))
+                print_directory(rp);
+        else {
+                char *split = strrchr(rp, '/');
+                if (split) {
+                        *split = '\0';
+                        char *rp2 = split + 1;
+                        if (arg_debug)
+                                printf("path %s, file %s\n", rp, rp2);
+                        print_file_or_dir(rp, rp2);
+                }
+        }
+        free(rp);
+}
+
+void cat(const char *path) {
+        EUID_ASSERT();
+        assert(path);
+
+        if (arg_debug)
+                printf("cat %s\n", path);
+        FILE *fp = fopen(path, "r");
+        if (!fp) {
+                fprintf(stderr, "Error: cannot read %s\n", path);
+                exit(1);
+        }
+        int fd = fileno(fp);
+        if (fd == -1)
+                errExit("fileno");
+        struct stat s;
+        if (fstat(fd, &s) == -1)
+                errExit("fstat");
+        if (!S_ISREG(s.st_mode)) {
+                fprintf(stderr, "Error: %s is not a regular file\n", path);
+                exit(1);
+        }
+        bool tty = isatty(STDOUT_FILENO);
+
+        int c;
+        while ((c = fgetc(fp)) != EOF) {
+                // file is untrusted
+                // replace control characters when printing to a terminal
+                if (tty && c != '\t' && c != '\n' && iscntrl((unsigned char) c))
+                        c = '?';
+                fputc(c, stdout);
+        }
+        fflush(stdout);
+        fclose(fp);
+}
+
 char *expand_path(const char *path) {
         char *fname = NULL;
         if (*path == '/') {
@@ -219,14 +281,14 @@ void sandboxfs(int op, pid_t pid, const char *path1, const char *path2) {
         check_join_permission(pid);
 
         // expand paths
-        char *fname1 = expand_path(path1);;
+        char *fname1 = expand_path(path1);
         char *fname2 = NULL;
         if (path2 != NULL) {
                 fname2 = expand_path(path2);
         }
         if (arg_debug) {
                 printf("file1 %s\n", fname1);
-                printf("file2 %s\n", fname2);
+                printf("file2 %s\n", fname2 ? fname2 : "(null)");
         }
 
         // sandbox root directory
@@ -234,57 +296,36 @@ void sandboxfs(int op, pid_t pid, const char *path1, const char *path2) {
         if (asprintf(&rootdir, "/proc/%d/root", pid) == -1)
                 errExit("asprintf");
 
-        if (op == SANDBOX_FS_LS) {
-                EUID_ROOT();
-                // chroot
-                if (chroot(rootdir) < 0)
-                        errExit("chroot");
-                if (chdir("/") < 0)
-                        errExit("chdir");
-
-                // drop privileges
-                drop_privs(0);
-
-                // check access
-                if (access(fname1, R_OK) == -1) {
-                        fprintf(stderr, "Error: Cannot access %s\n", fname1);
-                        exit(1);
-                }
-                /* coverity[toctou] */
-                char *rp = realpath(fname1, NULL);
-                if (!rp) {
-                        fprintf(stderr, "Error: Cannot access %s\n", fname1);
-                        exit(1);
-                }
-                if (arg_debug)
-                        printf("realpath %s\n", rp);
-
+        if (op == SANDBOX_FS_LS || op == SANDBOX_FS_CAT) {
+                pid_t child = fork();
+                if (child < 0)
+                        errExit("fork");
+                if (child == 0) {
+                        EUID_ROOT();
+                        // chroot
+                        if (chroot(rootdir) < 0)
+                                errExit("chroot");
+                        if (chdir("/") < 0)
+                                errExit("chdir");
 
-                // list directory contents
-                struct stat s;
-                if (stat(rp, &s) == -1) {
-                        fprintf(stderr, "Error: Cannot access %s\n", rp);
-                        exit(1);
-                }
-                if (S_ISDIR(s.st_mode)) {
-                        char *dir;
-                        if (asprintf(&dir, "%s/", rp) == -1)
-                                errExit("asprintf");
+                        // drop privileges
+                        drop_privs(0);
 
-                        print_directory(dir);
-                        free(dir);
-                }
-                else {
-                        char *split = strrchr(rp, '/');
-                        if (split) {
-                                *split = '\0';
-                                char *rp2 = split + 1;
-                                if (arg_debug)
-                                        printf("path %s, file %s\n", rp, rp2);
-                                print_file_or_dir(rp, rp2, 1);
-                        }
+                        if (op == SANDBOX_FS_LS)
+                                ls(fname1);
+                        else
+                                cat(fname1);
+#ifdef HAVE_GCOV
+                        __gcov_flush();
+#endif
+                        _exit(0);
                 }
-                free(rp);
+                // wait for the child to finish
+                int status = 0;
+                waitpid(child, &status, 0);
+                if (WIFEXITED(status) && WEXITSTATUS(status) == 0);
+                else
+                        exit(1);
         }
 
         // get file from sandbox and store it in the current directory
@@ -303,10 +344,12 @@ void sandboxfs(int op, pid_t pid, const char *path1, const char *path2) {
                 // create a user-owned temporary file in /run/firejail directory
                 char tmp_fname[] = "/run/firejail/tmpget-XXXXXX";
                 int fd = mkstemp(tmp_fname);
-                if (fd != -1) {
-                        SET_PERMS_FD(fd, getuid(), getgid(), 0600);
-                        close(fd);
+                if (fd == -1) {
+                        fprintf(stderr, "Error: cannot create temporary file %s\n", tmp_fname);
+                        exit(1);
                 }
+                SET_PERMS_FD(fd, getuid(), getgid(), 0600);
+                close(fd);
 
                 // copy the source file into the temporary file - we need to chroot
                 pid_t child = fork();
diff --git a/src/firejail/main.c b/src/firejail/main.c
index 4aa5311a2..1ffa6158c 100644
--- a/src/firejail/main.c
+++ b/src/firejail/main.c
@@ -811,6 +811,8 @@ static void run_cmd_and_exit(int i, int argc, char **argv) {
                          }
 
                         // list directory contents
+                        if (!arg_debug)
+                                 arg_quiet = 1;
                         pid_t pid = require_pid(argv[i] + 5);
                         sandboxfs(SANDBOX_FS_LS, pid, path, NULL);
                         exit(0);
@@ -818,6 +820,35 @@ static void run_cmd_and_exit(int i, int argc, char **argv) {
                 else
                         exit_err_feature("file transfer");
         }
+        else if (strncmp(argv[i], "--cat=", 6) == 0) {
+                if (checkcfg(CFG_FILE_TRANSFER)) {
+                        logargs(argc, argv);
+                        if (arg_private_cwd) {
+                                fprintf(stderr, "Error: --cat and --private-cwd options are mutually exclusive\n");
+                                exit(1);
+                        }
+
+                        if ((i + 2) != argc) {
+                                fprintf(stderr, "Error: invalid --cat option, path expected\n");
+                                exit(1);
+                        }
+                        char *path = argv[i + 1];
+                        invalid_filename(path, 0); // no globbing
+                        if (strstr(path, "..")) {
+                                fprintf(stderr, "Error: invalid file name %s\n", path);
+                                exit(1);
+                        }
+
+                        // write file contents to stdout
+                        if (!arg_debug)
+                                 arg_quiet = 1;
+                        pid_t pid = require_pid(argv[i] + 6);
+                        sandboxfs(SANDBOX_FS_CAT, pid, path, NULL);
+                        exit(0);
+                }
+                else
+                        exit_err_feature("file transfer");
+        }
 #endif
         else if (strncmp(argv[i], "--join=", 7) == 0) {
                 if (checkcfg(CFG_JOIN) || getuid() == 0) {
@@ -1159,8 +1190,7 @@ int main(int argc, char **argv, char **envp) {
 
                         // start the program directly without sandboxing
                         run_no_sandbox(argc, argv);
-                        // it will never get here!
-                        assert(0);
+                        __builtin_unreachable();
                 }
         }
         EUID_ASSERT();
@@ -1446,6 +1476,8 @@ int main(int argc, char **argv, char **envp) {
                                 if (config_seccomp_error_action == -1) {
                                         if (strcmp(argv[i] + 23, "kill") == 0)
                                                 arg_seccomp_error_action = SECCOMP_RET_KILL;
+                                        else if (strcmp(argv[i] + 23, "log") == 0)
+                                                arg_seccomp_error_action = SECCOMP_RET_LOG;
                                         else {
                                                 arg_seccomp_error_action = errno_find_name(argv[i] + 23);
                                                 if (arg_seccomp_error_action == -1)
diff --git a/src/firejail/output.c b/src/firejail/output.c
index 0e961bb61..36cb905cb 100644
--- a/src/firejail/output.c
+++ b/src/firejail/output.c
@@ -122,7 +122,8 @@ void check_output(int argc, char **argv) {
         }
         bool found_separator = false;
         /* copy argv into args, but drop --output(-stderr) arguments */
-        for (int i = 0, j = 0; i < argc; i++) {
+        int j;
+        for (i = 0, j = 0; i < argc; i++) {
                 if (!found_separator && i > 0) {
                         if (strncmp(argv[i], "--output=", 9) == 0) {
                                 continue;
diff --git a/src/firejail/profile.c b/src/firejail/profile.c
index 70acd8a2a..970033899 100644
--- a/src/firejail/profile.c
+++ b/src/firejail/profile.c
@@ -991,6 +991,8 @@ int profile_check_line(char *ptr, int lineno, const char *fname) {
                         if (config_seccomp_error_action == -1) {
                                 if (strcmp(ptr + 21, "kill") == 0)
                                         arg_seccomp_error_action = SECCOMP_RET_KILL;
+                                else if (strcmp(ptr + 21, "log") == 0)
+                                        arg_seccomp_error_action = SECCOMP_RET_LOG;
                                 else {
                                         arg_seccomp_error_action = errno_find_name(ptr + 21);
                                         if (arg_seccomp_error_action == -1)
diff --git a/src/firejail/protocol.c b/src/firejail/protocol.c
index 6402afbc6..a1594d6b9 100644
--- a/src/firejail/protocol.c
+++ b/src/firejail/protocol.c
@@ -90,7 +90,7 @@ void protocol_print_filter(pid_t pid) {
         exit(0);
 #else
         fwarning("--protocol not supported on this platform\n");
-        return;
+        exit(1);
 #endif
 }
 
diff --git a/src/firejail/sandbox.c b/src/firejail/sandbox.c
index 2314d5744..81d535762 100644
--- a/src/firejail/sandbox.c
+++ b/src/firejail/sandbox.c
@@ -140,6 +140,20 @@ void set_apparmor(void) {
 }
 #endif
 
+#ifdef HAVE_SECCOMP
+void seccomp_debug(void) {
+        if (arg_debug == 0)
+                return;
+
+        EUID_USER();
+        printf("Seccomp directory:\n");
+        ls(RUN_SECCOMP_DIR);
+        printf("Active seccomp files:\n");
+        cat(RUN_SECCOMP_LIST);
+        EUID_ROOT();
+}
+#endif
+
 static void save_nogroups(void) {
         if (arg_nogroups == 0)
                 return;
@@ -197,32 +211,6 @@ static FILE *create_ready_for_join_file(void) {
         }
 }
 
-#ifdef HAVE_SECCOMP
-static void seccomp_debug(void) {
-        if (arg_debug == 0)
-                return;
-
-        pid_t child = fork();
-        if (child < 0)
-                errExit("fork");
-        if (child == 0) {
-                // dropping privs before calling system(3)
-                drop_privs(1);
-                printf("Seccomp directory:\n");
-                int rv = system("ls -l "  RUN_SECCOMP_DIR);
-                (void) rv;
-                printf("Active seccomp files:\n");
-                rv = system("cat " RUN_SECCOMP_LIST);
-                (void) rv;
-#ifdef HAVE_GCOV
-                __gcov_flush();
-#endif
-                _exit(0);
-        }
-        waitpid(child, NULL, 0);
-}
-#endif
-
 static void sandbox_if_up(Bridge *br) {
         assert(br);
         if (!br->configured)
@@ -666,7 +654,8 @@ int sandbox(void* sandbox_arg) {
         // ... and mount a tmpfs on top of /run/firejail/mnt directory
         preproc_mount_mnt_dir();
         // bind-mount firejail binaries and helper programs
-        if (mount(LIBDIR "/firejail", RUN_FIREJAIL_LIB_DIR, "none", MS_BIND, NULL) < 0)
+        if (mount(LIBDIR "/firejail", RUN_FIREJAIL_LIB_DIR, NULL, MS_BIND, NULL) < 0 ||
+            mount(NULL, RUN_FIREJAIL_LIB_DIR, NULL, MS_RDONLY|MS_NOSUID|MS_NODEV|MS_BIND|MS_REMOUNT, NULL) < 0)
                 errExit("mounting " RUN_FIREJAIL_LIB_DIR);
 
         //****************************
diff --git a/src/firejail/sbox.c b/src/firejail/sbox.c
index cf3d3aeed..a92d62940 100644
--- a/src/firejail/sbox.c
+++ b/src/firejail/sbox.c
@@ -31,7 +31,7 @@
 #define O_PATH 010000000
 #endif
 
-static int sbox_do_exec_v(unsigned filtermask, char * const arg[]) {
+static int __attribute__((noreturn)) sbox_do_exec_v(unsigned filtermask, char * const arg[]) {
         // build a new, clean environment
         int env_index = 0;
         char *new_environment[256] = { NULL };
diff --git a/src/firejail/shutdown.c b/src/firejail/shutdown.c
index a7d0b2fbe..7e9628007 100644
--- a/src/firejail/shutdown.c
+++ b/src/firejail/shutdown.c
@@ -63,7 +63,9 @@ void shut(pid_t pid) {
                 sleep(1);
                 monsec--;
 
+                EUID_ROOT();
                 FILE *fp = fopen(monfile, "r");
+                EUID_USER();
                 if (!fp) {
                         killdone = 1;
                         break;
diff --git a/src/firejail/usage.c b/src/firejail/usage.c
index 4ab464289..2390706f2 100644
--- a/src/firejail/usage.c
+++ b/src/firejail/usage.c
@@ -47,6 +47,9 @@ static char *usage_str =
         "    --caps.drop=capability,capability - blacklist capabilities filter.\n"
         "    --caps.keep=capability,capability - whitelist capabilities filter.\n"
         "    --caps.print=name|pid - print the caps filter.\n"
+#ifdef HAVE_FILE_TRANSFER
+        "    --cat=name|pid filename - print content of file from sandbox container.\n"
+#endif
         "    --cgroup=tasks-file - place the sandbox in the specified control group.\n"
 #ifdef HAVE_CHROOT
         "    --chroot=dirname - chroot into directory.\n"
@@ -224,7 +227,8 @@ static char *usage_str =
         "    --seccomp.print=name|pid - print the seccomp filter for the sandbox\n"
         "\tidentified by name or PID.\n"
         "    --seccomp.32[.drop,.keep][=syscall] - like above but for 32 bit architecture.\n"
-        "    --seccomp-error-action=errno|kill - change error code or kill process.\n"
+        "    --seccomp-error-action=errno|kill|log - change error code, kill process\n"
+        "\tor log the attempt.\n"
 #endif
         "    --shell=none - run the program directly without a user shell.\n"
         "    --shell=program - set default user shell.\n"
diff --git a/src/firejail/x11.c b/src/firejail/x11.c
index 1ecb688af..e10abad4e 100644
--- a/src/firejail/x11.c
+++ b/src/firejail/x11.c
@@ -682,7 +682,7 @@ static char * get_title_arg_str() {
 }
 
 
-void x11_start_xpra_old(int argc, char **argv, int display, char *display_str) {
+static void __attribute__((noreturn)) x11_start_xpra_old(int argc, char **argv, int display, char *display_str) {
         EUID_ASSERT();
         int i;
         struct stat s;
@@ -921,7 +921,7 @@ void x11_start_xpra_old(int argc, char **argv, int display, char *display_str) {
 }
 
 
-void x11_start_xpra_new(int argc, char **argv, char *display_str) {
+static void __attribute__((noreturn)) x11_start_xpra_new(int argc, char **argv, char *display_str) {
         EUID_ASSERT();
         int i;
         pid_t server = 0;
diff --git a/src/firemon/firemon.h b/src/firemon/firemon.h
index 7a55a64fb..3fba486eb 100644
--- a/src/firemon/firemon.h
+++ b/src/firemon/firemon.h
@@ -46,13 +46,13 @@ void firemon_sleep(int st);
 
 
 // procevent.c
-void procevent(pid_t pid);
+void procevent(pid_t pid) __attribute__((noreturn));
 
 // usage.c
 void usage(void);
 
 // top.c
-void top(void);
+void top(void) __attribute__((noreturn));
 
 // list.c
 void list(void);
@@ -82,7 +82,7 @@ void cgroup(pid_t pid, int print_procs);
 void tree(pid_t pid);
 
 // netstats.c
-void netstats(void);
+void netstats(void) __attribute__((noreturn));
 
 // x11.c
 void x11(pid_t pid, int print_procs);
diff --git a/src/firemon/procevent.c b/src/firemon/procevent.c
index 7dd08444e..45964d3a2 100644
--- a/src/firemon/procevent.c
+++ b/src/firemon/procevent.c
@@ -220,7 +220,7 @@ errexit:
 }
 
 
-static int procevent_monitor(const int sock, pid_t mypid) {
+static void __attribute__((noreturn)) procevent_monitor(const int sock, pid_t mypid) {
         ssize_t len;
         struct nlmsghdr *nlmsghdr;
 
@@ -246,8 +246,7 @@ static int procevent_monitor(const int sock, pid_t mypid) {
 
                 int rv = select(max, &readfds, NULL, NULL, &tv);
                 if (rv == -1) {
-                        fprintf(stderr, "recv: %s\n", strerror(errno));
-                        return -1;
+                        errExit("recv");
                 }
 
                 // timeout
@@ -259,7 +258,7 @@ static int procevent_monitor(const int sock, pid_t mypid) {
 
 
                 if ((len = recv(sock, buf, sizeof(buf), 0)) == 0)
-                        return 0;
+                        exit(0);
                 if (len == -1) {
                         if (errno == EINTR)
                                 continue;
@@ -271,7 +270,7 @@ static int procevent_monitor(const int sock, pid_t mypid) {
                         }
                         else {
                                 fprintf(stderr,"Error: rx socket recv call, errno %d, %s\n", errno, strerror(errno));
-                                return -1;
+                                exit(1);
                         }
                 }
 
@@ -497,7 +496,7 @@ static int procevent_monitor(const int sock, pid_t mypid) {
                                 exit(0);
                 }
         }
-        return 0;
+        __builtin_unreachable();
 }
 
 void procevent(pid_t pid) {
@@ -515,6 +514,4 @@ void procevent(pid_t pid) {
         }
 
         procevent_monitor(sock, pid); // it will never return from here
-        assert(0);
-        close(sock); // quiet static analyzers
 }
diff --git a/src/fseccomp/main.c b/src/fseccomp/main.c
index 13eb3dfe7..f505ca0f3 100644
--- a/src/fseccomp/main.c
+++ b/src/fseccomp/main.c
@@ -20,7 +20,7 @@
 #include "fseccomp.h"
 #include "../include/seccomp.h"
 int arg_quiet = 0;
-int arg_seccomp_error_action = EPERM; // error action: errno or kill
+int arg_seccomp_error_action = EPERM; // error action: errno, log or kill
 
 static void usage(void) {
         printf("Usage:\n");
@@ -83,6 +83,8 @@ printf("\n");
         if (error_action) {
                 if (strcmp(error_action, "kill") == 0)
                         arg_seccomp_error_action = SECCOMP_RET_KILL;
+                else if (strcmp(error_action, "log") == 0)
+                        arg_seccomp_error_action = SECCOMP_RET_LOG;
                 else {
                         arg_seccomp_error_action = errno_find_name(error_action);
                         if (arg_seccomp_error_action == -1)
diff --git a/src/include/seccomp.h b/src/include/seccomp.h
index 50920ce3a..29b858c70 100644
--- a/src/include/seccomp.h
+++ b/src/include/seccomp.h
@@ -274,7 +274,7 @@ struct seccomp_data {
 #define RETURN_ERRNO(nr) \
         BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ERRNO | nr)
 
-extern int arg_seccomp_error_action;    // error action: errno or kill
+extern int arg_seccomp_error_action;    // error action: errno, log or kill
 #define KILL_OR_RETURN_ERRNO \
         BPF_STMT(BPF_RET+BPF_K, arg_seccomp_error_action)
 
diff --git a/src/include/syscall.h b/src/include/syscall.h
index 89b54170e..489da0600 100644
--- a/src/include/syscall.h
+++ b/src/include/syscall.h
@@ -32,7 +32,7 @@ void filter_add_blacklist_override(int fd, int syscall, int arg, void *ptrarg, b
 // errno.c
 void errno_print(void);
 int errno_find_name(const char *name);
-char *errno_find_nr(int nr);
+const char *errno_find_nr(int nr);
 
 // syscall.c
 void syscall_print(void);
diff --git a/src/lib/errno.c b/src/lib/errno.c
index d38c197ad..881c3b27e 100644
--- a/src/lib/errno.c
+++ b/src/lib/errno.c
@@ -183,7 +183,7 @@ int errno_find_name(const char *name) {
         return -1;
 }
 
-char *errno_find_nr(int nr) {
+const char *errno_find_nr(int nr) {
         int i;
         int elems = sizeof(errnolist) / sizeof(errnolist[0]);
         for (i = 0; i < elems; i++) {
diff --git a/src/man/firejail-profile.txt b/src/man/firejail-profile.txt
index 7b5653942..0784e7fd7 100644
--- a/src/man/firejail-profile.txt
+++ b/src/man/firejail-profile.txt
@@ -433,8 +433,10 @@ Enable seccomp filter and whitelist the system calls in the list.
 \fBseccomp.32.keep syscall,syscall,syscall
 Enable seccomp filter and whitelist the system calls in the list for 32 bit system calls on a 64 bit architecture system.
 .TP
-\fBseccomp-error-action kill | ERRNO
-Return a different error instead of EPERM to the process or kill it when an attempt is made to call a blocked system call.
+\fBseccomp-error-action kill | log | ERRNO
+Return a different error instead of EPERM to the process, kill it when
+an attempt is made to call a blocked system call, or allow but log the
+attempt.
 .TP
 \fBx11
 Enable X11 sandboxing.
diff --git a/src/man/firejail.txt b/src/man/firejail.txt
index 69cd4a7bc..3b7ba4e3d 100644
--- a/src/man/firejail.txt
+++ b/src/man/firejail.txt
@@ -273,6 +273,10 @@ $ firejail \-\-list
 $ firejail \-\-caps.print=3272
 
 .TP
+\fB\-\-cat=name|pid filename
+Print content of file from sandbox container, see FILE TRANSFER section for more details.
+
+.TP
 \fB\-\-cgroup=tasks-file
 Place the sandbox in the specified control group. tasks-file is the full path of cgroup tasks file.
 .br
@@ -344,7 +348,7 @@ $ firejail --dbus-system=filter --dbus-system.log --dbus-log=dbus.txt
 
 .TP
 \fB\-\-dbus-system=filter|none
-Set system DBus sandboxing policy. 
+Set system DBus sandboxing policy.
 .br
 
 .br
@@ -1059,7 +1063,7 @@ that are both writable and executable, to change mappings to be
 executable, or to create executable shared memory. The filter examines
 the arguments of mmap, mmap2, mprotect, pkey_mprotect, memfd_create
 and shmat system calls and returns error EPERM to the process (or
-kills it, see \-\-seccomp-error-action below) if necessary.
+kills it or log the attempt, see \-\-seccomp-error-action below) if necessary.
 .br
 
 .br
@@ -2122,8 +2126,8 @@ Instead of dropping the syscall by returning EPERM, another error
 number can be returned using \fBsyscall:errno\fR syntax. This can be
 also changed globally with \-\-seccomp-error-action or
 in /etc/firejail/firejail.config file.  The process can also be killed
-by using \fBsyscall:kill\fR syntax.
-
+by using \fBsyscall:kill\fR syntax, or the attempt may be logged with
+\fBsyscall:log\fR.
 .br
 
 .br
@@ -2193,7 +2197,8 @@ Instead of dropping the syscall by returning EPERM, another error
 number can be returned using \fBsyscall:errno\fR syntax. This can be
 also changed globally with \-\-seccomp-error-action or
 in /etc/firejail/firejail.config file.  The process can also be killed
-by using \fBsyscall:kill\fR syntax.
+by using \fBsyscall:kill\fR syntax, or the attempt may be logged with
+\fBsyscall:log\fR.
 .br
 
 .br
@@ -2402,7 +2407,8 @@ By default, if a seccomp filter blocks a system call, the process gets
 EPERM as the error. With \-\-seccomp-error-action=error, another error
 number can be returned, for example ENOSYS or EACCES. The process can
 also be killed (like in versions <0.9.63 of Firejail) by using
-\-\-seccomp-error-action=kill syntax. Not killing the process weakens
+\-\-seccomp-error-action=kill syntax, or the attempt may be logged
+with \-\-seccomp-error-action=log. Not killing the process weakens
 Firejail slightly when trying to contain intrusion, but it may also
 allow tighter filters if the only alternative is to allow a system
 call.
@@ -3029,6 +3035,12 @@ These features allow the user to inspect the filesystem container of an existing
 and transfer files between the container and the host filesystem.
 
 .TP
+\fB\-\-cat=name|pid filename
+Write content of a container file to standard out. The container is specified by name or PID.
+If standard out is a terminal, all ASCII control characters except new line and horizontal tab
+are replaced.
+
+.TP
 \fB\-\-get=name|pid filename
 Retrieve the container file and store it on the host in the current working directory.
 The container is specified by name or PID.
@@ -3072,6 +3084,10 @@ $ firejail \-\-get=mybrowser ~/Downloads/xpra-clipboard.png
 $ firejail \-\-put=mybrowser xpra-clipboard.png ~/Downloads/xpra-clipboard.png
 .br
 
+.br
+$ firejail \-\-cat=mybrowser ~/.bashrc
+.br
+
 .SH MONITORING
 Option \-\-list prints a list of all sandboxes. The format
 for each process entry is as follows:
@@ -3259,7 +3275,7 @@ Homepage: https://firejail.wordpress.com
 \&\flfirejail-profile\fR\|(5),
 \&\flfirejail-login\fR\|(5),
 \&\flfirejail-users\fR\|(5),
-.UR https://github.com/netblue30/firejail/wiki 
+.UR https://github.com/netblue30/firejail/wiki
 .UE ,
-.UR https://github.com/netblue30/firejail 
+.UR https://github.com/netblue30/firejail
 .UE