[PATCH v2] tools/power/x86/intel-speed-select: Harden daemon pidfile open

Srinivas Pandruvada
2026-04-26T15:09:30Z

From: Ali Ahmet MEMIS <dev@unknownbbqr.xyz>

Avoid symlink-based pidfile clobbering by opening the pidfile with
O_NOFOLLOW and validating it with fstat() before locking/writing.

The daemon currently uses a fixed pidfile path under /tmp. A local
unprivileged user can pre-create a symlink at that path and cause a
root-run daemon instance to write into an attacker-chosen file.

Fixes: 7fd786dfbd2c ("tools/power/x86/intel-speed-select: OOB daemon mode")
Signed-off-by: Ali Ahmet MEMIS <dev@unknownbbqr.xyz>
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: stable@kernel.org
---
[Fixed commit message for long lines]

v2
- Added CC to stable

tools/power/x86/intel-speed-select/isst-daemon.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/tools/power/x86/intel-speed-select/isst-daemon.c b/tools/power/x86/intel-speed-select/isst-daemon.c
index 66df21b2b573..acedb7432849 100644
--- a/tools/power/x86/intel-speed-select/isst-daemon.c
+++ b/tools/power/x86/intel-speed-select/isst-daemon.c
@@ -148,6 +148,7 @@ static void daemonize(char *rundir, char *pidfile)
{
int pid, sid, i;
char str[10];
+ struct stat st;
struct sigaction sig_actions;
sigset_t sig_set;
int ret;
@@ -200,11 +201,17 @@ static void daemonize(char *rundir, char *pidfile)
if (ret == -1)
exit(EXIT_FAILURE);

- pid_file_handle = open(pidfile, O_RDWR | O_CREAT, 0600);
+ pid_file_handle = open(pidfile, O_RDWR | O_CREAT | O_NOFOLLOW, 0600);
if (pid_file_handle == -1) {
/* Couldn't open lock file */
exit(1);
}
+
+ if (fstat(pid_file_handle, &st) == -1)
+ exit(1);
+
+ if (!S_ISREG(st.st_mode))
+ exit(1);
/* Try to lock file */
#ifdef LOCKF_SUPPORT
if (lockf(pid_file_handle, F_TLOCK, 0) == -1) {
--
2.52.0