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 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: ipc-msg-make-msgrcv-work-with-long_min.patch and it can be found in the queue-4.4 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 @@ -742,7 +742,10 @@ 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-4.4/ipc-msg-make-msgrcv-work-with-long_min.patch queue-4.4/fs-fcntl-f_setown-avoid-undefined-behaviour.patch queue-4.4/pm-sleep-declare-__tracedata-symbols-as-char-rather-than-char.patch queue-4.4/x86-cpu-intel-introduce-macros-for-intel-family-numbers.patch queue-4.4/x86-retpoline-fill-rsb-on-context-switch-for-affected-cpus.patch queue-4.4/acpi-scan-prefer-devices-without-_hid-_cid-for-_adr-matching.patch queue-4.4/time-avoid-undefined-behaviour-in-ktime_add_safe.patch