Patch "ipc: msg, make msgrcv work with LONG_MIN" has been added to the 3.18-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    ipc: msg, make msgrcv work with LONG_MIN

to the 3.18-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ipc-msg-make-msgrcv-work-with-long_min.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 999898355e08ae3b92dfd0a08db706e0c6703d30 Mon Sep 17 00:00:00 2001
From: Jiri Slaby <jslaby@suse.cz>
Date: Wed, 14 Dec 2016 15:06:07 -0800
Subject: ipc: msg, make msgrcv work with LONG_MIN

From: Jiri Slaby <jslaby@suse.cz>

commit 999898355e08ae3b92dfd0a08db706e0c6703d30 upstream.

When LONG_MIN is passed to msgrcv, one would expect to recieve any
message.  But convert_mode does *msgtyp = -*msgtyp and -LONG_MIN is
undefined.  In particular, with my gcc -LONG_MIN produces -LONG_MIN
again.

So handle this case properly by assigning LONG_MAX to *msgtyp if
LONG_MIN was specified as msgtyp to msgrcv.

This code:
  long msg[] = { 100, 200 };
  int m = msgget(IPC_PRIVATE, IPC_CREAT | 0644);
  msgsnd(m, &msg, sizeof(msg), 0);
  msgrcv(m, &msg, sizeof(msg), LONG_MIN, 0);

produces currently nothing:

  msgget(IPC_PRIVATE, IPC_CREAT|0644)     = 65538
  msgsnd(65538, {100, "\310\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"}, 16, 0) = 0
  msgrcv(65538, ...

Except a UBSAN warning:

  UBSAN: Undefined behaviour in ipc/msg.c:745:13
  negation of -9223372036854775808 cannot be represented in type 'long int':

With the patch, I see what I expect:

  msgget(IPC_PRIVATE, IPC_CREAT|0644)     = 0
  msgsnd(0, {100, "\310\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"}, 16, 0) = 0
  msgrcv(0, {100, "\310\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"}, 16, -9223372036854775808, 0) = 16

Link: http://lkml.kernel.org/r/20161024082633.10148-1-jslaby@suse.cz
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 ipc/msg.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -740,7 +740,10 @@ static inline int convert_mode(long *msg
 	if (*msgtyp == 0)
 		return SEARCH_ANY;
 	if (*msgtyp < 0) {
-		*msgtyp = -*msgtyp;
+		if (*msgtyp == LONG_MIN) /* -LONG_MIN is undefined */
+			*msgtyp = LONG_MAX;
+		else
+			*msgtyp = -*msgtyp;
 		return SEARCH_LESSEQUAL;
 	}
 	if (msgflg & MSG_EXCEPT)


Patches currently in stable-queue which might be from jslaby@suse.cz are

queue-3.18/ipc-msg-make-msgrcv-work-with-long_min.patch