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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: 3eb39f4793 ("signal: add pidfd_send_signal() syscall")
Signed-off-by: Jann Horn <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>
This commit is contained in:
Jann Horn 2019-03-30 03:12:32 +01:00 • committed by Christian Brauner
commit 556a888a14
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1 changed files with 4 additions and 9 deletions
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13
kernel/signal.c
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@ -3605,16 +3605,11 @@ 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);
}