Fixed --resolve-symlinks when mountpoint name starts with source dir name.

Fixes #122

3 files changed, 45 insertions, 2 deletions

diff --git a/src/bindfs.c b/src/bindfs.c
index 65384dc..263aa0e 100644
--- a/src/bindfs.c
+++ b/src/bindfs.c
@@ -393,10 +393,10 @@ static char *process_path(const char *path, bool resolve_symlinks)
                    we want to be able to operate on broken symlinks. */
                 return strdup(path);
             }
-        } else if (strncmp(result, settings.mntdest, settings.mntdest_len) == 0) {
+        } else if (path_starts_with(result, settings.mntdest, settings.mntdest_len)) {
             /* Recursive call. We cannot handle this without deadlocking,
                especially in single-threaded mode. */
-            DPRINTF("Denying recursive access to mountpoint `%s'", result);
+            DPRINTF("Denying recursive access to mountpoint \"%s\" at \"%s\"", settings.mntdest, result);
             free(result);
             errno = EPERM;
             return NULL;
diff --git a/src/misc.c b/src/misc.c
index cedd247..122497d 100644
--- a/src/misc.c
+++ b/src/misc.c
@@ -135,6 +135,45 @@ const char *my_dirname(char *path)
     }
 }
 
+static const char* find_last_char_between(const char* start, const char* end, char ch) {
+    assert(start != NULL && end != NULL);
+    const char* p = end - 1;
+    while (p >= start) {
+        if (*p == ch) {
+            return p;
+        }
+        --p;
+    }
+    return NULL;
+}
+
+bool path_starts_with(const char *path, const char* prefix, size_t prefix_len)
+{
+    size_t path_len = strlen(path);
+    while (prefix_len > 0 && prefix[prefix_len - 1] == '/') {
+        --prefix_len;
+    }
+    while (path_len > 0 && path[path_len - 1] == '/') {
+        --path_len;
+    }
+
+    if (strncmp(path, prefix, prefix_len) == 0) {
+        // We still need to check that the last path component of
+        // 'path' does not simply start with the last path component of 'prefix'.
+        const char* prefix_slash = find_last_char_between(prefix, prefix + prefix_len, '/');
+        const char* prefix_part = prefix_slash ? prefix_slash + 1 : prefix;
+        size_t prefix_part_len = (prefix + prefix_len - prefix_part);
+
+        const char* path_part = path + (prefix_part - prefix);
+        const char* path_slash = strchr(path_part, '/');
+        size_t path_part_len = path_slash ? path_slash - path_part : path_len - (path_part - path);
+
+        return prefix_part_len == path_part_len;
+    }
+
+    return false;
+}
+
 static char **dup_argv(int argc, const char * const *argv, struct arena *arena)
 {
     char **pointer_list = arena_malloc(arena, (argc + 1) * sizeof(char*));
diff --git a/src/misc.h b/src/misc.h
index 360ddd1..07c0472 100644
--- a/src/misc.h
+++ b/src/misc.h
@@ -53,6 +53,10 @@ const char *my_basename(const char *path);
    Otherwise, returns ".". */
 const char *my_dirname(char *path);
 
+/* Returns true if the initial path components of 'path' are the path components of 'prefix'.
+   Assumes 'strlen(prefix) == prefix_len'. */
+bool path_starts_with(const char *path, const char* prefix, size_t prefix_len);
+
 /* Filters arguments in comma-separated lists prefixed by '-o'.
  * Allocates 'new_argv' and its strings, as well as some temporary data, into 'arena'. */
 void filter_o_opts(