CVE-2011-1182: Insufficient Information (NVD-CWE-noinfo)
value: kernel/signal.c in the Linux kernel before 2.6.39 allows local users to spoof the uid and pid of a signal sender via a sigqueueinfo system call.
CWE description: There is insufficient information about the issue to classify it; details are unkown or unspecified.
Published: 2013-03-01T12:37Z
Repository: https://github.com/torvalds/linux
Language: C
Files changed: kernel/signal.c
Commit date: 2011-03-21 14:23:43 -0700
Commit message: 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: diff --git a/kernel/signal.c b/kernel/signal.c
index 4e3cff10fdce..31751868de88 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2419,13 +2419,17 @@ SYSCALL_DEFINE3(rt_sigqueueinfo, pid_t, pid, int, sig,
 
 	if (copy_from_user(&info, uinfo, sizeof(siginfo_t)))
 		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.  */
 	return kill_proc_info(sig, &info, pid);
 }
@@ -2435,13 +2439,17 @@ long do_rt_tgsigqueueinfo(pid_t tgid, pid_t pid, int sig, siginfo_t *info)
 	/* This is only valid for single tasks */
 	if (pid <= 0 || tgid <= 0)
 		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);
 }
 

Vulnerable code: 	   Nor can they impersonate a kill(), which adds source info.  */
	if (info.si_code >= 0)
	   Nor can they impersonate a kill(), which adds source info.  */
	if (info->si_code >= 0)
Fixed code: 	 * 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);
	}
	 * 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);
	}