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

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File and Resource Handling: Medium

The PulseAudio protocol server socket initialization uses stat() to
check for existing socket files before unlinking and rebinding. This has
the same two vulnerabilities recently fixed in module-protocol-native:

1. stat() follows symlinks, so an attacker who places a symlink at the
   socket path (e.g., in XDG_RUNTIME_DIR/pulse/) can trick the daemon
   into unlinking the symlink target.

2. The gap between stat() and unlink() creates a TOCTOU race window.

Fix by using lstat() instead of stat() and adding an explicit symlink
check that refuses to proceed if the path is a symbolic link, consistent
with the approach in module-protocol-native.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Wim Taymans 2026-04-24 14:20:45 +02:00
parent a6155387da
commit 84f8230a47
1 changed files with 7 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

8
src/modules/module-protocol-pulse/server.c
View file

@ -614,7 +614,7 @@ static int start_unix_server(struct server *server, const struct sockaddr_storag
goto error; goto error;
} }
if (stat(addr_un->sun_path, &socket_stat) < 0) { if (lstat(addr_un->sun_path, &socket_stat) < 0) {
if (errno != ENOENT) { if (errno != ENOENT) {
res = -errno; res = -errno;
pw_log_warn("server %p: stat('%s') failed: %m", pw_log_warn("server %p: stat('%s') failed: %m",
@ -622,6 +622,12 @@ static int start_unix_server(struct server *server, const struct sockaddr_storag
goto error_close; goto error_close;
} }
} }
else if (S_ISLNK(socket_stat.st_mode)) {
res = -EACCES;
pw_log_error("server %p: refusing to follow symlink at '%s'",
server, addr_un->sun_path);
goto error_close;
}
else if (socket_stat.st_mode & S_IWUSR || socket_stat.st_mode & S_IWGRP) { else if (socket_stat.st_mode & S_IWUSR || socket_stat.st_mode & S_IWGRP) {
if (!S_ISSOCK(socket_stat.st_mode)) { if (!S_ISSOCK(socket_stat.st_mode)) {
res = -EEXIST; res = -EEXIST;