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UPSTREAM: signal: don't silently convert SI_USER signals to non-current pidfd

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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: I004452c19c50296730a2c6852a5ef47abd69d819
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
This commit is contained in:
Jann Horn 2019-03-30 03:12:32 +01:00 • committed by Joel Fernandes (Google)
commit 74c14d6081
1 changed files with 4 additions and 9 deletions
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13
kernel/signal.c
View file

@ -3381,16 +3381,11 @@ 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);
}