[PATCH Trusty SRU] ipc: fix compat msgrcv with negative msgtyp

[tim.gardner at canonical.com]

From: Mateusz Guzik <mguzik at redhat.com>

BugLink: http://bugs.launchpad.net/bugs/1393355

Compat function takes msgtyp argument as u32 and passes it down to
do_msgrcv which results in casting to long, thus the sign is lost and we
get a big positive number instead.

Cast the argument to signed type before passing it down.

Signed-off-by: Mateusz Guzik <mguzik at redhat.com>
Reported-by: Gabriellla Schmidt <gsc at bruker.de>
Cc: Al Viro <viro at zeniv.linux.org.uk>
Cc: Davidlohr Bueso <davidlohr at hp.com>
Cc: Manfred Spraul <manfred at colorfullife.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
(cherry picked from commit e7ca2552369c1dfe0216c626baf82c3d83ec36bb)
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
---
 ipc/compat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ipc/compat.c b/ipc/compat.c
index 892f658..d3b3760 100644
--- a/ipc/compat.c
+++ b/ipc/compat.c
@@ -381,7 +381,7 @@ COMPAT_SYSCALL_DEFINE6(ipc, u32, call, int, first, int, second,
 			uptr = compat_ptr(ipck.msgp);
 			fifth = ipck.msgtyp;
 		}
-		return do_msgrcv(first, uptr, second, fifth, third,
+		return do_msgrcv(first, uptr, second, (s32)fifth, third,
 				 compat_do_msg_fill);
 	}
 	case MSGGET:
-- 
2.1.3