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Fix "fuse: failed to exec fusermount: Permission denied" #18

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Fix "fuse: failed to exec fusermount: Permission denied" #18

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ea36919
Fix "fuse: failed to exec fusermount: Permission denied"
danpla Oct 24, 2023
a0fd529
Merge branch 'main' into fix-fusermount-permission-error
probonopd Oct 28, 2023
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74 changes: 26 additions & 48 deletions patches/libfuse/mount.c.diff
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
diff --git a/lib/mount.c b/lib/mount.c
index d71e6fc55..acc1711ff 100644
index d71e6fc..fce39e3 100644
--- a/lib/mount.c
+++ b/lib/mount.c
@@ -41,7 +41,6 @@
Expand All @@ -10,78 +10,55 @@ index d71e6fc55..acc1711ff 100644
#define FUSE_COMMFD_ENV "_FUSE_COMMFD"

#ifndef HAVE_FORK
@@ -117,17 +116,79 @@ static const struct fuse_opt fuse_mount_opts[] = {
@@ -117,17 +116,56 @@ static const struct fuse_opt fuse_mount_opts[] = {
FUSE_OPT_END
};

+int fileExists(const char* path);
+char* findBinaryInFusermountDir(const char* binaryName);
+
+int fileExists(const char* path) {
+ FILE* file = fopen(path, "r");
+ if (file) {
+ fclose(file);
+ return 1;
+ }
+ return 0;
+}
+
+char* findBinaryInFusermountDir(const char* binaryName) {
+ // For security reasons, we do not search the binary on the $PATH;
+ // instead, we check if the binary exists in FUSERMOUNT_DIR
+ // as defined in meson.build
+ char* binaryPath = malloc(strlen(FUSERMOUNT_DIR) + strlen(binaryName) + 2);
+ strcpy(binaryPath, FUSERMOUNT_DIR);
+ strcat(binaryPath, "/");
+ strcat(binaryPath, binaryName);
+ if (fileExists(binaryPath)) {
+ return binaryPath;
+ }
+
+ // If the binary does not exist in FUSERMOUNT_DIR, return NULL
+ return NULL;
+}
+
+static const char *fuse_mount_prog(void)
+{
+ // Check if the FUSERMOUNT_PROG environment variable is set and if so, use it
+ const char *prog = getenv("FUSERMOUNT_PROG");
+ if (prog) {
+ if (access(prog, X_OK) == 0)
+ return prog;
+ }
+ if (prog && access(prog, X_OK) == 0)
+ return prog;
+
+ // Check if there is a binary "fusermount3"
+ prog = findBinaryInFusermountDir("fusermount3");
+ prog = FUSERMOUNT_DIR "/fusermount3";
+ if (access(prog, X_OK) == 0)
+ return prog;
Comment on lines 17 to 27
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Since this function can be evaluated several times (once in exec_fusermount and the second time for its argv), it should probably always either return a pointer to a static buffer (filled only once), or allocate the string on the heap (we can assign the returned pointer to a static variable so that the function is called only once).

An alternative is to just use argv[0] in exec_fusermount instead of calling fuse_mount_prog the second time (or probably do the opposite: fill argv[0] with fuse_mount_prog right inside exec_fusermount).

+
+ // Check if there is a binary called "fusermount"
+ // This is known to work for our purposes
+ prog = findBinaryInFusermountDir("fusermount");
+ // On modern sysems, it can be a symlink (e.g. to "fusermount3")
+ prog = FUSERMOUNT_DIR "/fusermount";
+ if (access(prog, X_OK) == 0)
+ return prog;
+
+ // For i = 4...99, check if there is a binary called "fusermount" + i
+ // It is not yet known whether this will work for our purposes, but it is better than not even attempting
+ for (int i = 4; i < 100; i++) {
+ prog = findBinaryInFusermountDir("fusermount" + i);
+ if (access(prog, X_OK) == 0)
+ return prog;
+ static char buf[256];
+ const int ret = snprintf(buf, sizeof(buf), "%s/fusermount%i", FUSERMOUNT_DIR, i);
+ if (ret < 0 || ret == sizeof(buf)) {
+ fuse_log(FUSE_LOG_ERR, "fuse: snprintf for fusermount path failed\n");
+ break;
+ }
+
+ if (access(buf, X_OK) == 0)
+ return buf;
+ }
+
+ // If all else fails, return NULL
+ fuse_log(FUSE_LOG_ERR, "fuse: Can't find fusermount binary\n");
+ _exit(1);
+
+ // Silence possible compiler warnings.
+ return NULL;
+}
+
static void exec_fusermount(const char *argv[])
{
- execv(FUSERMOUNT_DIR "/" FUSERMOUNT_PROG, (char **) argv);
- execvp(FUSERMOUNT_PROG, (char **) argv);
+ const char *fusermount_prog = fuse_mount_prog();
+ if (fusermount_prog) {
+ execv(fusermount_prog, (char **) argv);
+ }
+ execv(fuse_mount_prog(), (char **) argv);
}

void fuse_mount_version(void)
Expand All @@ -93,7 +70,7 @@ index d71e6fc55..acc1711ff 100644
exec_fusermount(argv);
_exit(1);
} else if (pid != -1)
@@ -300,7 +361,7 @@ void fuse_kern_unmount(const char *mountpoint, int fd)
@@ -300,7 +338,7 @@ void fuse_kern_unmount(const char *mountpoint, int fd)
return;

if(pid == 0) {
Expand All @@ -102,7 +79,7 @@ index d71e6fc55..acc1711ff 100644
"--", mountpoint, NULL };

exec_fusermount(argv);
@@ -346,7 +407,7 @@ static int setup_auto_unmount(const char *mountpoint, int quiet)
@@ -346,7 +384,7 @@ static int setup_auto_unmount(const char *mountpoint, int quiet)
}
}

Expand All @@ -111,7 +88,7 @@ index d71e6fc55..acc1711ff 100644
argv[a++] = "--auto-unmount";
argv[a++] = "--";
argv[a++] = mountpoint;
@@ -407,7 +468,7 @@ static int fuse_mount_fusermount(const char *mountpoint, struct mount_opts *mo,
@@ -407,7 +445,7 @@ static int fuse_mount_fusermount(const char *mountpoint, struct mount_opts *mo,
}
}

Expand All @@ -120,11 +97,12 @@ index d71e6fc55..acc1711ff 100644
if (opts) {
argv[a++] = "-o";
argv[a++] = opts;
@@ -421,7 +482,7 @@ static int fuse_mount_fusermount(const char *mountpoint, struct mount_opts *mo,
@@ -421,7 +459,7 @@ static int fuse_mount_fusermount(const char *mountpoint, struct mount_opts *mo,
snprintf(env, sizeof(env), "%i", fds[0]);
setenv(FUSE_COMMFD_ENV, env, 1);
exec_fusermount(argv);
- perror("fuse: failed to exec fusermount3");
+ perror("fuse: failed to exec fusermount");
_exit(1);
}