UPSTREAM: signal: don't silently convert SI_USER signals to non-current pidfd
The current sys_pidfd_send_signal() silently turns signals with explicit
SI_USER context that are sent to non-current tasks into signals with
kernel-generated siginfo.
This is unlike do_rt_sigqueueinfo(), which returns -EPERM in this case.
If a user actually wants to send a signal with kernel-provided siginfo,
they can do that with pidfd_send_signal(pidfd, sig, NULL, 0); so allowing
this case is unnecessary.
Instead of silently replacing the siginfo, just bail out with an error;
this is consistent with other interfaces and avoids special-casing behavior
based on security checks.
Fixes: 3eb39f47934f ("signal: add pidfd_send_signal() syscall")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Christian Brauner <christian@brauner.io>
(cherry picked from commit 556a888a14afe27164191955618990fb3ccc9aad)
Bug: 135608568
Test: test program using syscall(__NR_pidfd_send_signal,..) to send SIGKILL
Change-Id: I493af671b82c43bff1425ee24550d2fb9aa6d961
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
diff --git a/kernel/signal.c b/kernel/signal.c
index 4ed8492..3da9502 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3038,16 +3038,11 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
if (unlikely(sig != kinfo.si_signo))
goto err;
+ /* Only allow sending arbitrary signals to yourself. */
+ ret = -EPERM;
if ((task_pid(current) != pid) &&
- (kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL)) {
- /* Only allow sending arbitrary signals to yourself. */
- ret = -EPERM;
- if (kinfo.si_code != SI_USER)
- goto err;
-
- /* Turn this into a regular kill signal. */
- prepare_kill_siginfo(sig, &kinfo);
- }
+ (kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL))
+ goto err;
} else {
prepare_kill_siginfo(sig, &kinfo);
}