Prevent rt_sigqueueinfo and rt_tgsigqueueinfo from spoofing the signal code
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>
diff --git a/kernel/signal.c b/kernel/signal.c
index 4e3cff1..3175186 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2421,9 +2421,13 @@
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 @@
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);
