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

srinivas pandruvada
2026-04-23T20:51:29Z

On Thu, 2026-04-23 at 22:32 +0300, unknownbbqrx wrote:
>
> From: ali <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.
>
> Signed-off-by: ali <dev@unknownbbqr.xyz>

Thanks for the patch, I am sorry, but I still can't take it in this
state. It's still an anonymous contribution, which is against policy.

> ---
>  tools/power/x86/intel-speed-select/isst-daemon.c | 12 +++++++++++-
>  1 file changed, 11 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 66df21b2b..4346b049d 100644
> --- a/tools/power/x86/intel-speed-select/isst-daemon.c
> +++ b/tools/power/x86/intel-speed-select/isst-daemon.c
> @@ -200,11 +200,21 @@ 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);
>   }
> +
> + {
> + struct stat st;
> +
> + if (fstat(pid_file_handle, &st) == -1)
> + exit(1);
> +
> + if (!S_ISREG(st.st_mode))
> + exit(1);
> + }

Also move struct stat st out at the top of function. So we don't do
unnecessary indentation with { }.

>   /* Try to lock file */
>  #ifdef LOCKF_SUPPORT
>   if (lockf(pid_file_handle, F_TLOCK, 0) == -1) {
>
> base-commit: 2e68039281932e6dc37718a1ea7cbb8e2cda42e6