mount.c.diff

diff --git a/lib/mount.c b/lib/mount.c
index d71e6fc55..acc1711ff 100644
--- a/lib/mount.c
+++ b/lib/mount.c
@@ -41,7 +41,6 @@
 #define umount2(mnt, flags) unmount(mnt, (flags == 2) ? MNT_FORCE : 0)
 #endif
 
-#define FUSERMOUNT_PROG		"fusermount3"
 #define FUSE_COMMFD_ENV		"_FUSE_COMMFD"
 
 #ifndef HAVE_FORK
@@ -117,17 +116,79 @@ 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;
+	}
+
+	// Check if there is a binary "fusermount3"
+	prog = findBinaryInFusermountDir("fusermount3");
+	if (access(prog, X_OK) == 0)
+		return prog;
+
+	// Check if there is a binary called "fusermount"
+	// This is known to work for our purposes
+	prog = findBinaryInFusermountDir("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;
+	}
+
+	// If all else fails, return NULL
+	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);
+	}
 }
 
 void fuse_mount_version(void)
 {
 	int pid = fork();
 	if (!pid) {
-		const char *argv[] = { FUSERMOUNT_PROG, "--version", NULL };
+		const char *argv[] = { fuse_mount_prog(), "--version", NULL };
 		exec_fusermount(argv);
 		_exit(1);
 	} else if (pid != -1)
@@ -300,7 +361,7 @@ void fuse_kern_unmount(const char *mountpoint, int fd)
 		return;
 
 	if(pid == 0) {
-		const char *argv[] = { FUSERMOUNT_PROG, "-u", "-q", "-z",
+		const char *argv[] = { fuse_mount_prog(), "-u", "-q", "-z",
 				       "--", mountpoint, NULL };
 
 		exec_fusermount(argv);
@@ -346,7 +407,7 @@ static int setup_auto_unmount(const char *mountpoint, int quiet)
 			}
 		}
 
-		argv[a++] = FUSERMOUNT_PROG;
+		argv[a++] = fuse_mount_prog();
 		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,
 			}
 		}
 
-		argv[a++] = FUSERMOUNT_PROG;
+		argv[a++] = fuse_mount_prog();
 		if (opts) {
 			argv[a++] = "-o";
 			argv[a++] = opts;
@@ -421,7 +482,7 @@ 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);
 	}