port whitelist path creation to "at" family of functions

2 files changed, 131 insertions, 68 deletions

diff --git a/src/firejail/fs_home.c b/src/firejail/fs_home.c
index 3afa3bf0c..09931bd56 100644
--- a/src/firejail/fs_home.c
+++ b/src/firejail/fs_home.c
@@ -290,6 +290,8 @@ void fs_private(void) {
         if (u == 0 && arg_allusers) // allow --allusers when starting the sandbox as root
                 ;
         else {
+                if (arg_allusers)
+                        fwarning("--allusers disabled by --private or --whitelist\n");
                 if (mount("tmpfs", "/home", "tmpfs", MS_NOSUID | MS_NODEV | MS_NOEXEC | MS_STRICTATIME | MS_REC,  "mode=755,gid=0") < 0)
                         errExit("mounting home directory");
                 fs_logger("tmpfs /home");
diff --git a/src/firejail/fs_whitelist.c b/src/firejail/fs_whitelist.c
index 0178e3c5b..df0c21e12 100644
--- a/src/firejail/fs_whitelist.c
+++ b/src/firejail/fs_whitelist.c
@@ -51,46 +51,75 @@ char *parse_nowhitelist(int nowhitelist_flag, char *ptr1) {
 
 static int mkpath(const char* path, mode_t mode) {
         assert(path && *path);
-
         mode |= 0111;
 
         // create directories with uid/gid as root or as current user if inside home directory
-        uid_t uid = getuid();
-        gid_t gid = getgid();
-        if (strncmp(path, cfg.homedir, strlen(cfg.homedir)) != 0) {
-                uid = 0;
-                gid = 0;
+        if (strncmp(path, cfg.homedir, strlen(cfg.homedir)) == 0) {
+                EUID_USER();
         }
 
         // work on a copy of the path
-        char *file_path = strdup(path);
-        if (!file_path)
+        char *dup = strdup(path);
+        if (!dup)
                 errExit("strdup");
 
-        char* p;
+        // don't create the last path element
+        char *p = strrchr(dup, '/');
+        if (!p)
+                errExit("strrchr");
+        *p = '\0';
+
+        int parentfd = open("/", O_PATH|O_DIRECTORY|O_CLOEXEC);
+        if (parentfd == -1)
+                errExit("open");
+
+        // traverse the path, return -1 if a symlink is encountered
         int done = 0;
-        for (p=strchr(file_path+1, '/'); p; p=strchr(p+1, '/')) {
-                *p='\0';
-                if (mkdir(file_path, mode)==-1) {
+        int fd = -1;
+        char *tok = strtok(dup, "/");
+        if (!tok)
+                errExit("strtok");
+        while (tok) {
+                // skip all instances of "/./"
+                if (strcmp(tok, ".") == 0) {
+                        tok = strtok(NULL, "/");
+                        continue;
+                }
+                // create the directory if necessary
+                if (mkdirat(parentfd, tok, mode) == -1) {
                         if (errno != EEXIST) {
-                                *p='/';
-                                free(file_path);
+                                if (arg_debug || arg_debug_whitelists)
+                                        perror("mkdir");
+                                close(parentfd);
+                                free(dup);
+                                EUID_ROOT();
                                 return -1;
                         }
                 }
-                else {
-                        if (set_perms(file_path, uid, gid, mode))
-                                errExit("set_perms");
+                else
                         done = 1;
+                // open the directory
+                fd = openat(parentfd, tok, O_PATH|O_DIRECTORY|O_NOFOLLOW|O_CLOEXEC);
+                if (fd == -1) {
+                        if (arg_debug || arg_debug_whitelists)
+                                perror("open");
+                        close(parentfd);
+                        free(dup);
+                        EUID_ROOT();
+                        return -1;
                 }
-
-                *p='/';
+                // move on to next path segment
+                close(parentfd);
+                parentfd = fd;
+                tok = strtok(NULL, "/");
         }
+
         if (done)
                 fs_logger2("mkpath", path);
 
-        free(file_path);
-        return 0;
+        free(dup);
+        EUID_ROOT();
+        return fd;
 }
 
 static void whitelist_path(ProfileEntry *entry) {
@@ -184,13 +213,18 @@ static void whitelist_path(ProfileEntry *entry) {
         }
         assert(wfile);
 
-        // check if the file exists, confirm again there is no symlink
+        if (arg_debug || arg_debug_whitelists)
+                printf("Whitelisting %s\n", path);
+
+        // confirm again the mount source exists and there is no symlink
         struct stat wfilestat;
 #ifndef TEST_MOUNTINFO
         EUID_USER();
         int fd = safe_fd(wfile, O_PATH|O_NOFOLLOW|O_CLOEXEC);
         EUID_ROOT();
         if (fd == -1) {
+                if (arg_debug || arg_debug_whitelists)
+                        printf("Debug %d: skip whitelisting of %s\n", __LINE__, path);
                 free(wfile);
                 return;
         }
@@ -198,57 +232,64 @@ static void whitelist_path(ProfileEntry *entry) {
                 errExit("fstat");
         close(fd);
         if (S_ISLNK(wfilestat.st_mode)) {
+                if (arg_debug || arg_debug_whitelists)
+                        printf("Debug %d: skip whitelisting of %s\n", __LINE__, path);
                 free(wfile);
                 return;
         }
 #endif
 
-        if (arg_debug || arg_debug_whitelists)
-                printf("Whitelisting %s\n", path);
+        // create path of the mount target if necessary
+        int fd2 = mkpath(path, 0755);
+        if (fd2 == -1) {
+                // something went wrong during path creation or a symlink was found;
+                // if there is a symlink somewhere in the path of the mount target,
+                // assume the file is whitelisted already
+                if (arg_debug || arg_debug_whitelists)
+                        printf("Debug %d: skip whitelisting of %s\n", __LINE__, path);
+                free(wfile);
+                return;
+        }
 
-        // create the path if necessary
-        struct stat s;
-        if (stat(path, &s) == -1) {
-                mkpath(path, 0755);
-                if (S_ISDIR(wfilestat.st_mode)) {
-                        int rv = mkdir(path, 0755);
-                        if (rv) {
-                                fprintf(stderr, "Error: cannot create directory %s\n", path);
-                                exit(1);
-                        }
-                }
-                else {
-                        int fd2 = open(path, O_RDONLY|O_CREAT|O_EXCL|O_CLOEXEC, S_IRUSR|S_IWUSR);
-                        if (fd2 == -1) {
-                                fprintf(stderr, "Error: cannot create empty file %s\n", path);
-                                exit(1);
+        // get file name of the mount target
+        const char *file = gnu_basename(path);
+
+        // create the mount target if necessary and open it, a symlink is rejected
+        int fd3 = -1;
+        if (S_ISDIR(wfilestat.st_mode)) {
+                // directory foo can exist already:
+                // firejail --whitelist=/foo/bar --whitelist=/foo
+                if (mkdirat(fd2, file, 0755) == -1 && errno != EEXIST) {
+                        if (arg_debug || arg_debug_whitelists) {
+                                perror("mkdir");
+                                printf("Debug %d: skip whitelisting of %s\n", __LINE__, path);
                         }
                         close(fd2);
+                        free(wfile);
+                        return;
                 }
+                fd3 = openat(fd2, file, O_PATH|O_DIRECTORY|O_NOFOLLOW|O_CLOEXEC);
         }
         else {
-                if (!S_ISDIR(s.st_mode)) {
-                        free(wfile);
-                        return; // the file is already present
-                }
+                // create an empty file, fails with EEXIST if it is whitelisted already:
+                // firejail --whitelist=/foo --whitelist=/foo/bar
+                fd3 = openat(fd2, file, O_RDONLY|O_CREAT|O_EXCL|O_CLOEXEC, S_IRUSR|S_IWUSR);
         }
 
-        fs_logger2("whitelist", path);
-
-        // get a file descriptor for path; if path contains anything other than directories
-        // or a regular file, assume it is whitelisted already
-        int fd3 = safe_fd(path, O_PATH|O_NOFOLLOW|O_CLOEXEC);
         if (fd3 == -1) {
+                if (arg_debug || arg_debug_whitelists) {
+                        if (errno != EEXIST) {
+                                perror("open");
+                                printf("Debug %d: skip whitelisting of %s\n", __LINE__, path);
+                        }
+                }
+                close(fd2);
                 free(wfile);
                 return;
         }
-        if (fstat(fd3, &s) == -1)
-                errExit("fstat");
-        if (!(S_ISDIR(s.st_mode) || S_ISREG(s.st_mode))) {
-                free(wfile);
-                close(fd3);
-                return;
-        }
+        close(fd2);
+
+        fs_logger2("whitelist", path);
 
         // mount via the link in /proc/self/fd
         char *proc;
@@ -272,6 +313,7 @@ static void whitelist_path(ProfileEntry *entry) {
         int fd4 = safe_fd(path, O_PATH|O_NOFOLLOW|O_CLOEXEC);
         if (fd4 == -1)
                 errExit("safe_fd");
+        struct stat s;
         if (fstat(fd4, &s) == -1)
                 errExit("fstat");
         if (s.st_dev != wfilestat.st_dev || s.st_ino != wfilestat.st_ino)
@@ -501,6 +543,14 @@ void fs_whitelist(void) {
                         goto errexit;
                 }
 
+                // no trailing slash and no trailing dot
+                char *p = strrchr(new_name, '/');
+                if (!p)
+                        errExit("strrchr");
+                if (*(p + 1) == '\0')
+                        goto errexit;
+                if (*(p + 1) == '.' && *(p + 2) == '\0')
+                        goto errexit;
 
                 // extract the absolute path of the file
                 // realpath function will fail with ENOENT if the file is not found
@@ -577,7 +627,6 @@ void fs_whitelist(void) {
                         continue;
                 }
 
-
                 // check for supported directories
                 if (strncmp(new_name, cfg.homedir, strlen(cfg.homedir)) == 0) {
                         // whitelisting home directory is disabled if --private option is present
@@ -597,7 +646,7 @@ void fs_whitelist(void) {
 
                         // both path and absolute path are under /home
                         if (strncmp(fname, cfg.homedir, strlen(cfg.homedir)) == 0) {
-                                // avoid naming issues, also entire home dirs are not allowed
+                                // entire home directory is not allowed
                                 if (*(fname + strlen(cfg.homedir)) != '/')
                                         goto errexit;
                         }
@@ -744,7 +793,7 @@ void fs_whitelist(void) {
                         entry->link = new_name;
                 else {
                         free(new_name);
-                        new_name = NULL;
+                        entry->link = NULL;
                 }
 
                 // change file name in entry->data
@@ -774,7 +823,7 @@ void fs_whitelist(void) {
                         if (mount(cfg.homedir, RUN_WHITELIST_HOME_USER_DIR, NULL, MS_BIND|MS_REC, NULL) < 0)
                                 errExit("mount bind");
 
-                        // mount a tmpfs and initialize /home/user
+                        // mount a tmpfs and initialize /home/user, overrides --allusers
                         fs_private();
                 }
                 else
@@ -986,14 +1035,29 @@ void fs_whitelist(void) {
                         // if the link is already there, do not bother
                         if (lstat(entry->link, &s) != 0) {
                                 // create the path if necessary
-                                mkpath(entry->link, 0755);
-
-                                int rv = symlink(entry->data + 10, entry->link);
-                                if (rv)
-                                        fprintf(stderr, "Warning cannot create symbolic link %s\n", entry->link);
+                                int fd = mkpath(entry->link, 0755);
+                                if (fd == -1) {
+                                        if (arg_debug || arg_debug_whitelists)
+                                                printf("Debug %d: cannot create symbolic link %s\n", __LINE__, entry->link);
+                                        free(entry->link);
+                                        entry = entry->next;
+                                        continue;
+                                }
+                                // get file name of symlink
+                                const char *file = gnu_basename(entry->link);
+                                // create the link
+                                int rv = symlinkat(entry->data + 10, fd, file);
+                                if (rv) {
+                                        if (arg_debug || arg_debug_whitelists) {
+                                                perror("symlink");
+                                                printf("Debug %d: cannot create symbolic link %s\n", __LINE__, entry->link);
+                                        }
+                                }
                                 else if (arg_debug || arg_debug_whitelists)
                                         printf("Created symbolic link %s -> %s\n", entry->link, entry->data + 10);
+                                close(fd);
                         }
+                        free(entry->link);
                 }
 
                 entry = entry->next;
@@ -1076,9 +1140,6 @@ void fs_whitelist(void) {
                 fs_logger2("tmpfs", RUN_WHITELIST_MODULE_DIR);
         }
 
-        if (new_name)
-                free(new_name);
-
         return;
 
 errexit: