[PATCH 3.10 28/34] ipc: fix compat msgrcv with negative msgtyp

[Greg Kroah-Hartman]

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

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

From: Mateusz Guzik <mguzik@xxxxxxxxxx>

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>
Cc: Masanari Iida <standby24x7@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 ipc/compat.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/ipc/compat.c
+++ b/ipc/compat.c
@@ -381,7 +381,7 @@ COMPAT_SYSCALL_DEFINE6(ipc, u32, call, i
 			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:


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