[PATCH 3.12 010/122] ipc: fix compat msgrcv with negative msgtyp

[Jiri Slaby]

From: Mateusz Guzik <mguzik@xxxxxxxxxx>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit e7ca2552369c1dfe0216c626baf82c3d83ec36bb upstream.

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@xxxxxxxxxx>
Reported-by: Gabriellla Schmidt <gsc@xxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Davidlohr Bueso <davidlohr@xxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
 ipc/compat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ipc/compat.c b/ipc/compat.c
index 892f6585dd60..d3b376025e9b 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:
-- 
2.2.2

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