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security: fix TOCTOU race and symlink following in native protocol socket

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File and Resource Handling: Medium

The socket initialization code uses stat() followed by unlink() to clean
up stale socket files. This creates two issues:

1. stat() follows symlinks, so an attacker who places a symlink at the
   socket path can trick the daemon into unlinking an arbitrary file.

2. The gap between stat() and unlink() creates a TOCTOU race window
   where the file could be replaced between the check and the removal.

Fix by using lstat() to detect symlinks without following them, refusing
to proceed if the path is a symlink, and only unlinking files that are
actually sockets (S_ISSOCK). This narrows the race window and prevents
symlink-based file deletion attacks.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Wim Taymans 2026-04-24 14:11:47 +02:00
parent 4c9ec363a3
commit 613b35eedf
1 changed files with 8 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

10
src/modules/module-protocol-native.c
View file

@ -931,14 +931,20 @@ static int add_socket(struct pw_protocol *protocol, struct server *s, struct soc
s->addr.sun_path[0] = 0; s->addr.sun_path[0] = 0;
size = (socklen_t) (strlen(&s->addr.sun_path[1]) + 1); size = (socklen_t) (strlen(&s->addr.sun_path[1]) + 1);
} else { } else {
if (stat(s->addr.sun_path, &socket_stat) < 0) { if (lstat(s->addr.sun_path, &socket_stat) < 0) {
if (errno != ENOENT) { if (errno != ENOENT) {
res = -errno; res = -errno;
pw_log_error("server %p: stat %s failed with error: %m", pw_log_error("server %p: stat %s failed with error: %m",
s, s->addr.sun_path); s, s->addr.sun_path);
goto error_close; goto error_close;
} }
} else if (socket_stat.st_mode & S_IWUSR || socket_stat.st_mode & S_IWGRP) { } else if (S_ISLNK(socket_stat.st_mode)) {
pw_log_error("server %p: refusing to follow symlink at %s",
s, s->addr.sun_path);
res = -EACCES;
goto error_close;
} else if (S_ISSOCK(socket_stat.st_mode) &&
(socket_stat.st_mode & S_IWUSR || socket_stat.st_mode & S_IWGRP)) {
unlink(s->addr.sun_path); unlink(s->addr.sun_path);
} }
size = (socklen_t) (strlen(s->addr.sun_path) + 1); size = (socklen_t) (strlen(s->addr.sun_path) + 1);