[PATCH 3.16 171/346] arm: oabi compat: add missing access checks

[Ben Hutchings]

3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Dave Weinstein <olorin@xxxxxxxxxx>

commit 7de249964f5578e67b99699c5f0b405738d820a2 upstream.

Add access checks to sys_oabi_epoll_wait() and sys_oabi_semtimedop().
This fixes CVE-2016-3857, a local privilege escalation under
CONFIG_OABI_COMPAT.

Reported-by: Chiachih Wu <wuchiachih@xxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Nicolas Pitre <nico@xxxxxxxxxx>
Signed-off-by: Dave Weinstein <olorin@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/arm/kernel/sys_oabi-compat.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/arch/arm/kernel/sys_oabi-compat.c
+++ b/arch/arm/kernel/sys_oabi-compat.c
@@ -279,8 +279,12 @@ asmlinkage long sys_oabi_epoll_wait(int
 	mm_segment_t fs;
 	long ret, err, i;
 
-	if (maxevents <= 0 || maxevents > (INT_MAX/sizeof(struct epoll_event)))
+	if (maxevents <= 0 ||
+			maxevents > (INT_MAX/sizeof(*kbuf)) ||
+			maxevents > (INT_MAX/sizeof(*events)))
 		return -EINVAL;
+	if (!access_ok(VERIFY_WRITE, events, sizeof(*events) * maxevents))
+		return -EFAULT;
 	kbuf = kmalloc(sizeof(*kbuf) * maxevents, GFP_KERNEL);
 	if (!kbuf)
 		return -ENOMEM;
@@ -317,6 +321,8 @@ asmlinkage long sys_oabi_semtimedop(int
 
 	if (nsops < 1 || nsops > SEMOPM)
 		return -EINVAL;
+	if (!access_ok(VERIFY_READ, tsops, sizeof(*tsops) * nsops))
+		return -EFAULT;
 	sops = kmalloc(sizeof(*sops) * nsops, GFP_KERNEL);
 	if (!sops)
 		return -ENOMEM;