join: move to mmapped sandbox status indicator

1) close #3612
2) remove an implicit limitation on rlimit-fsize option
(could not set limit to smaller than 6 bytes without affecting
the ability to join a sandbox)
3) rename 'join-or-start' file to just 'join'
4)  when waiting for a sandbox that is not fully configured yet,
increase polling frequency from 10 per second to 100 per second

4 files changed, 39 insertions, 76 deletions

diff --git a/src/firejail/firejail.h b/src/firejail/firejail.h
index 85139d75f..2bb8dd351 100644
--- a/src/firejail/firejail.h
+++ b/src/firejail/firejail.h
@@ -370,8 +370,9 @@ void check_user_namespace(void);
 char *guess_shell(void);
 
 // sandbox.c
+#define SANDBOX_DONE '1'
 int sandbox(void* sandbox_arg);
-void start_application(int no_sandbox, FILE *fp) __attribute__((noreturn));
+void start_application(int no_sandbox, char *set_sandbox_status) __attribute__((noreturn));
 void set_apparmor(void);
 
 // network_main.c
diff --git a/src/firejail/join.c b/src/firejail/join.c
index 14eea4612..c7619ef3b 100644
--- a/src/firejail/join.c
+++ b/src/firejail/join.c
@@ -292,7 +292,7 @@ static void extract_umask(pid_t pid) {
                 fprintf(stderr, "Error: cannot open umask file\n");
                 exit(1);
         }
-        if (fscanf(fp, "%3o", &orig_umask) < 1) {
+        if (fscanf(fp, "%o", &orig_umask) != 1) {
                 fprintf(stderr, "Error: cannot read umask\n");
                 exit(1);
         }
@@ -303,66 +303,33 @@ static void extract_umask(pid_t pid) {
 // it is no firejail sandbox at all, return true if the sandbox is complete
 bool is_ready_for_join(const pid_t pid) {
         EUID_ASSERT();
-        // check if a file "ready-for-join" exists
+        // check if a file /run/firejail/mnt/join exists
         char *fname;
-        if (asprintf(&fname, "/proc/%d/root%s", pid, RUN_READY_FOR_JOIN) == -1)
+        if (asprintf(&fname, "/proc/%d/root%s", pid, RUN_JOIN_FILE) == -1)
                 errExit("asprintf");
         EUID_ROOT();
-        FILE *fp = fopen(fname, "re");
+        int fd = open(fname, O_RDONLY|O_CLOEXEC);
         EUID_USER();
         free(fname);
-        if (!fp)
-                return false;
-        // regular file owned by root
-        int fd = fileno(fp);
         if (fd == -1)
-                errExit("fileno");
+                return false;
         struct stat s;
         if (fstat(fd, &s) == -1)
                 errExit("fstat");
         if (!S_ISREG(s.st_mode) || s.st_uid != 0) {
-                fclose(fp);
+                close(fd);
                 return false;
         }
-        // check if it is non-empty
-        char buf[BUFLEN];
-        if (fgets(buf, BUFLEN, fp) == NULL) {
-                fclose(fp);
-                return false;
+        char status;
+        if (read(fd, &status, 1) == 1 && status == SANDBOX_DONE) {
+                close(fd);
+                return true;
         }
-        fclose(fp);
-        // confirm "ready" string was written
-        if (strcmp(buf, "ready\n") != 0)
-                return false;
-
-        // walk down the process tree a few nodes, there should be no firejail leaf
-#define MAXNODES 5
-        pid_t current = pid, next;
-        int i;
-        for (i = 0; i < MAXNODES; i++) {
-                if (find_child(current, &next) == 1) {
-                        // found a leaf
-                        EUID_ROOT();
-                        char *comm = pid_proc_comm(current);
-                        EUID_USER();
-                        if (!comm) {
-                                fprintf(stderr, "Error: cannot read /proc file\n");
-                                exit(1);
-                        }
-                        if (strcmp(comm, "firejail") == 0) {
-                                free(comm);
-                                return false;
-                        }
-                        free(comm);
-                        break;
-                }
-                current = next;
-        }
-
-        return true;
+        close(fd);
+        return false;
 }
 
-#define SNOOZE 100000 // sleep interval in microseconds
+#define SNOOZE 10000 // sleep interval in microseconds
 void check_join_permission(pid_t pid) {
         // check if pid belongs to a fully set up firejail sandbox
         unsigned long i;
diff --git a/src/firejail/sandbox.c b/src/firejail/sandbox.c
index 0965b1017..ef09a790c 100644
--- a/src/firejail/sandbox.c
+++ b/src/firejail/sandbox.c
@@ -20,6 +20,7 @@
 
 #include "firejail.h"
 #include "../include/seccomp.h"
+#include <sys/mman.h>
 #include <sys/mount.h>
 #include <sys/wait.h>
 #include <sys/stat.h>
@@ -204,16 +205,17 @@ static void save_umask(void) {
         }
 }
 
-static FILE *create_ready_for_join_file(void) {
-        FILE *fp = fopen(RUN_READY_FOR_JOIN, "wxe");
-        if (fp) {
-                ASSERT_PERMS_STREAM(fp, 0, 0, 0644);
-                return fp;
-        }
-        else {
-                fprintf(stderr, "Error: cannot create %s\n", RUN_READY_FOR_JOIN);
-                exit(1);
-        }
+static char *create_join_file(void) {
+        int fd = open(RUN_JOIN_FILE, O_RDWR|O_CREAT|O_EXCL|O_CLOEXEC, S_IRUSR | S_IWRITE | S_IRGRP | S_IROTH);
+        if (fd == -1)
+                errExit("open");
+        if (ftruncate(fd, 1) == -1)
+                errExit("ftruncate");
+        char *rv = mmap(NULL, 1, PROT_WRITE, MAP_SHARED, fd, 0);
+        if (rv == MAP_FAILED)
+                errExit("mmap");
+        close(fd);
+        return rv;
 }
 
 static void sandbox_if_up(Bridge *br) {
@@ -472,7 +474,7 @@ static int ok_to_run(const char *program) {
         return 0;
 }
 
-void start_application(int no_sandbox, FILE *fp) {
+void start_application(int no_sandbox, char *set_sandbox_status) {
         // set environment
         if (no_sandbox == 0) {
                 env_defaults();
@@ -492,16 +494,14 @@ void start_application(int no_sandbox, FILE *fp) {
         if (arg_audit) {
                 assert(arg_audit_prog);
 
-                if (fp) {
-                        fprintf(fp, "ready\n");
-                        fclose(fp);
-                }
 #ifdef HAVE_GCOV
                 __gcov_dump();
 #endif
 #ifdef HAVE_SECCOMP
                 seccomp_install_filters();
 #endif
+                if (set_sandbox_status)
+                        *set_sandbox_status = SANDBOX_DONE;
                 execl(arg_audit_prog, arg_audit_prog, NULL);
 
                 perror("execl");
@@ -530,16 +530,14 @@ void start_application(int no_sandbox, FILE *fp) {
 
                 int rv = ok_to_run(cfg.original_argv[cfg.original_program_index]);
 
-                if (fp) {
-                        fprintf(fp, "ready\n");
-                        fclose(fp);
-                }
 #ifdef HAVE_GCOV
                 __gcov_dump();
 #endif
 #ifdef HAVE_SECCOMP
                 seccomp_install_filters();
 #endif
+                if (set_sandbox_status)
+                        *set_sandbox_status = SANDBOX_DONE;
                 if (rv)
                         execvp(cfg.original_argv[cfg.original_program_index], &cfg.original_argv[cfg.original_program_index]);
                 else
@@ -591,16 +589,14 @@ void start_application(int no_sandbox, FILE *fp) {
                 if (!arg_command && !arg_quiet)
                         print_time();
 
-                if (fp) {
-                        fprintf(fp, "ready\n");
-                        fclose(fp);
-                }
 #ifdef HAVE_GCOV
                 __gcov_dump();
 #endif
 #ifdef HAVE_SECCOMP
                 seccomp_install_filters();
 #endif
+                if (set_sandbox_status)
+                        *set_sandbox_status = SANDBOX_DONE;
                 execvp(arg[0], arg);
         }
 
@@ -1162,11 +1158,10 @@ int sandbox(void* sandbox_arg) {
         set_caps();
 
         //****************************************
-        // communicate progress of sandbox set up
-        // to --join
+        // relay status information to join option
         //****************************************
 
-        FILE *rj = create_ready_for_join_file();
+        char *set_sandbox_status = create_join_file();
 
         //****************************************
         // create a new user namespace
@@ -1248,10 +1243,10 @@ int sandbox(void* sandbox_arg) {
                         set_nice(cfg.nice);
                 set_rlimits();
 
-                start_application(0, rj);
+                start_application(0, set_sandbox_status);
         }
 
-        fclose(rj);
+        munmap(set_sandbox_status, 1);
 
         int status = monitor_application(app_pid);      // monitor application
         flush_stdin();
diff --git a/src/include/rundefs.h b/src/include/rundefs.h
index d56623907..4da2db748 100644
--- a/src/include/rundefs.h
+++ b/src/include/rundefs.h
@@ -113,7 +113,7 @@
 #define RUN_FSLOGGER_FILE               RUN_MNT_DIR "/fslogger"
 #define RUN_TRACE_FILE                  RUN_MNT_DIR "/trace"
 #define RUN_UMASK_FILE                  RUN_MNT_DIR "/umask"
+#define RUN_JOIN_FILE                   RUN_MNT_DIR "/join"
 #define RUN_OVERLAY_ROOT                RUN_MNT_DIR "/oroot"
-#define RUN_READY_FOR_JOIN              RUN_MNT_DIR "/ready-for-join"
 
 #endif