Prevent rt_sigqueueinfo and rt_tgsigqueueinfo from spoofing the signal code (da48524e) · Commits · 戴 / test

Userland should be able to trust the pid and uid of the sender of a signal if the si_code is SI_TKILL. Unfortunately, the kernel has historically allowed sigqueueinfo() to send any si_code at all (as long as it was negative - to distinguish it from kernel-generated signals like SIGILL etc), so it could spoof a SI_TKILL with incorrect siginfo values. Happily, it looks like glibc has always set si_code to the appropriate SI_QUEUE, so there are probably no actual user code that ever uses anything but the appropriate SI_QUEUE flag. So just tighten the check for si_code (we used to allow any negative value), and add a (one-time) warning in case there are binaries out there that might depend on using other si_code values. Signed-off-by:

Julien Tinnes <jln@google.com> Acked-by:

Oleg Nesterov <oleg@redhat.com> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

kernel/signal.c

+12 −4

Original line number	Diff line number	Diff line
		@@ -2421,9 +2421,13 @@ SYSCALL_DEFINE3(rt_sigqueueinfo, pid_t, pid, int, sig,
		return -EFAULT;

		/* Not even root can pretend to send signals from the kernel.
		Nor can they impersonate a kill(), which adds source info. */
		if (info.si_code >= 0)
		* Nor can they impersonate a kill()/tgkill(), which adds source info.
		*/
		if (info.si_code != SI_QUEUE) {
		/* We used to allow any < 0 si_code */
		WARN_ON_ONCE(info.si_code < 0);
		return -EPERM;
		}
		info.si_signo = sig;

		/* POSIX.1b doesn't mention process groups. */
		@@ -2437,9 +2441,13 @@ long do_rt_tgsigqueueinfo(pid_t tgid, pid_t pid, int sig, siginfo_t *info)
		return -EINVAL;

		/* Not even root can pretend to send signals from the kernel.
		Nor can they impersonate a kill(), which adds source info. */
		if (info->si_code >= 0)
		* Nor can they impersonate a kill()/tgkill(), which adds source info.
		*/
		if (info->si_code != SI_QUEUE) {
		/* We used to allow any < 0 si_code */
		WARN_ON_ONCE(info->si_code < 0);
		return -EPERM;
		}
		info->si_signo = sig;

		return do_send_specific(tgid, pid, sig, info);

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