[PATCH 3.10-rc7] Fix: kernel/ptrace.c: ptrace_peek_siginfo() missing __put_user() validation

[Mathieu Desnoyers <mathieu.desnoyers@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.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Andrey Vagin <avagin@openvz.org>
CC: Roland McGrath <roland@redhat.com>
CC: Oleg Nesterov <oleg@redhat.com>
CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
CC: David Howells <dhowells@redhat.com>
CC: Dave Jones <davej@redhat.com>
CC: Pavel Emelyanov <xemul@parallels.com>
CC: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pedro Alves <palves@redhat.com>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Linus Torvalds <torvalds@linux-foundation.org>
---
 kernel/ptrace.c |   20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

Index: linux/kernel/ptrace.c
===================================================================
--- linux.orig/kernel/ptrace.c
+++ linux/kernel/ptrace.c
@@ -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);

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