Fix: kernel/ptrace.c: ptrace_peek_siginfo() missing __put_user() validation

This __put_user() could be used by unprivileged processes to write into kernel memory. The issue here is that even if copy_siginfo_to_user() fails, the error code is not checked before __put_user() is executed. Luckily, ptrace_peek_siginfo() has been added within the 3.10-rc cycle, so it has not hit a stable release yet.

Signed-off-by Mathieu Desnoyers <[email protected]>

CC Andrey Vagin <[email protected]>

CC Roland McGrath <[email protected]>

CC Oleg Nesterov <[email protected]>

CC "Paul E. McKenney" <[email protected]>

CC David Howells <[email protected]>

CC Dave Jones <[email protected]>

CC Pavel Emelyanov <[email protected]>

CC Linus Torvalds <[email protected]>

Cc Pedro Alves <[email protected]>

CC Andrew Morton <[email protected]>

CC Linus Torvalds <[email protected]>

---
 kernel/ptrace.c |   20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

Index: linux/kernel/ptrace.c
===================================================================

kernel/ptrace.c +11 -9

@@ -665,20 +665,22 @@ static int ptrace_peek_siginfo(struct ta
 		if (unlikely(is_compat_task())) {
 			compat_siginfo_t __user *uinfo = compat_ptr(data);
 
-			ret = copy_siginfo_to_user32(uinfo, &info);
-			ret |= __put_user(info.si_code, &uinfo->si_code);
+			if (copy_siginfo_to_user32(uinfo, &info) ||
+			    __put_user(info.si_code, &uinfo->si_code)) {
+				ret = -EFAULT;
+				break;
+			}
+
 		} else
 #endif
 		{
 			siginfo_t __user *uinfo = (siginfo_t __user *) data;
 
-			ret = copy_siginfo_to_user(uinfo, &info);
-			ret |= __put_user(info.si_code, &uinfo->si_code);
-		}
-
-		if (ret) {
-			ret = -EFAULT;
-			break;
+			if (copy_siginfo_to_user(uinfo, &info) ||
+			    __put_user(info.si_code, &uinfo->si_code)) {
+				ret = -EFAULT;
+				break;
+			}
 		}
 
 		data += sizeof(siginfo_t);

Signature · 4 lines

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

This __put_user() could be used by unprivileged processes to write into kernel memory. The issue here is that even if copy_siginfo_to_user() fails, the error code is not checked before __put_user() is executed. Luckily, ptrace_peek_siginfo() has been added within the 3.10-rc cycle, so it has not hit a stable release yet.