Find usermountN using execve and set FUSERMOUNT_PROG if not set

Author: probonopd

src/runtime/runtime.c

@@ -5,7 +5,7 @@
  * as possible (one .c file) and use as few external dependencies
  * as possible
  *
- * Copyright (c) 2004-22 Simon Peter
+ * Copyright (c) 2004-24 Simon Peter
  * Portions Copyright (c) 2007 Alexander Larsson
  * Portions from WjCryptLib_Md5 originally written by Alexander Peslyak,
    modified by WaterJuice retaining Public Domain license
@@ -62,6 +62,10 @@ extern int sqfs_opt_proc(void* data, const char* arg, int key, struct fuse_args*
 #include <sys/mman.h>
 #include <stdint.h>
 #include <libgen.h>
+#include <dirent.h>
+#include <ctype.h>
+
+const char* fusermountPath = NULL;
 
 typedef struct {
     uint32_t lo;
@@ -405,6 +409,93 @@ int appimage_print_binary(char* fname, unsigned long offset, unsigned long lengt
 	return 0;
 }
 
+char* find_fusermount() {
+    char* fusermount_base = "fusermount";
+
+    char* fusermount_path = getenv("PATH");
+    if (fusermount_path == NULL) {
+        return NULL;
+    }
+
+    char* path_copy = strdup(fusermount_path);
+    char* dir = strtok(path_copy, ":");
+
+    while (dir != NULL) {
+        DIR* dir_ptr = opendir(dir);
+        if (dir_ptr == NULL) {
+            dir = strtok(NULL, ":");
+            continue;
+        }
+
+        struct dirent* entry;
+        while ((entry = readdir(dir_ptr)) != NULL) {
+            // Check if the entry starts with "fusermount"
+            if (strncmp(entry->d_name, fusermount_base, 10) == 0) {
+                // Check if the rest of the entry is a digit
+                char* suffix = entry->d_name + 10;
+                int j = 0;
+                while (suffix[j] != '\0' && isdigit(suffix[j])) {
+                    j++;
+                }
+
+                if (suffix[j] == '\0') {
+                    // Construct the full path of the entry
+                    char* fusermount_full_path = malloc(strlen(dir) + strlen(entry->d_name) + 2);
+                    sprintf(fusermount_full_path, "%s/%s", dir, entry->d_name);
+
+                    // Check if the binary is setuid root
+                    struct stat sb;
+                    if (stat(fusermount_full_path, &sb) == -1) {
+                        perror("stat");
+                        free(fusermount_full_path);
+                        continue;
+                    }
+
+                    if (sb.st_uid != 0 || (sb.st_mode & S_ISUID) == 0) {
+                        // Not setuid root, skip this binary
+                        free(fusermount_full_path);
+                        continue;
+                    }
+
+                    pid_t pid = fork();
+                    if (pid == -1) {
+                        perror("fork");
+                        free(fusermount_full_path);
+                        continue;
+                    }
+
+                    if (pid == 0) {
+                        // Child process
+                        char* args[] = {fusermount_full_path, "--version", NULL};
+                        execvp(fusermount_full_path, args);
+                        // If execvp returns, it means the executable was not found
+                        exit(1);
+                    } else {
+                        // Parent process
+                        int status;
+                        waitpid(pid, &status, 0);
+
+                        if (WIFEXITED(status) && WEXITSTATUS(status) == 0) {
+                            // The executable was found and executed successfully
+                            closedir(dir_ptr);
+                            free(path_copy);
+                            return fusermount_full_path;
+                        }
+
+                        free(fusermount_full_path);
+                    }
+                }
+            }
+        }
+
+        closedir(dir_ptr);
+        dir = strtok(NULL, ":");
+    }
+
+    free(path_copy);
+    return NULL;
+}
+
 /* Exit status to use when launching an AppImage fails.
  * For applications that assign meanings to exit status codes (e.g. rsync),
  * we avoid "cluttering" pre-defined exit status codes by using 127 which
@@ -1600,6 +1691,18 @@ int main(int argc, char* argv[]) {
     if (pid == 0) {
         /* in child */
 
+        fusermountPath = getenv("FUSERMOUNT_PROG");
+        if (fusermountPath == NULL) {
+            char* new_prog = find_fusermount();
+            if (new_prog != NULL) {
+                setenv("FUSERMOUNT_PROG", new_prog, 1);
+                // printf("FUSERMOUNT_PROG set to %s\n", new_prog);
+                free(new_prog);
+            } else {
+                printf("Error: No suitable fusermount binary found on the $PATH\n");
+            }
+        }
+
         char* child_argv[5];
 
         /* close read pipe */