[3.13.y.z extended stable] Patch "eventpoll: fix uninitialized variable in epoll_ctl" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    eventpoll: fix uninitialized variable in epoll_ctl

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.9.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

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>From 18abd109213aea3e827ac401975b223b5ee00ec3 Mon Sep 17 00:00:00 2001
From: Nicolas Iooss <nicolas.iooss_linux at m4x.org>
Date: Tue, 9 Sep 2014 14:50:51 -0700
Subject: eventpoll: fix uninitialized variable in epoll_ctl
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

commit c680e41b3a2e944185c74bf60531e3d316d3ecc4 upstream.

When calling epoll_ctl with operation EPOLL_CTL_DEL, structure epds is
not initialized but ep_take_care_of_epollwakeup reads its event field.
When this unintialized field has EPOLLWAKEUP bit set, a capability check
is done for CAP_BLOCK_SUSPEND in ep_take_care_of_epollwakeup.  This
produces unexpected messages in the audit log, such as (on a system
running SELinux):

    type=AVC msg=audit(1408212798.866:410): avc:  denied
    { block_suspend } for  pid=7754 comm="dbus-daemon" capability=36
    scontext=unconfined_u:unconfined_r:unconfined_t
    tcontext=unconfined_u:unconfined_r:unconfined_t
    tclass=capability2 permissive=1

    type=SYSCALL msg=audit(1408212798.866:410): arch=c000003e syscall=233
    success=yes exit=0 a0=3 a1=2 a2=9 a3=7fffd4d66ec0 items=0 ppid=1
    pid=7754 auid=1000 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0
    fsgid=0 tty=(none) ses=3 comm="dbus-daemon"
    exe="/usr/bin/dbus-daemon"
    subj=unconfined_u:unconfined_r:unconfined_t key=(null)

("arch=c000003e syscall=233 a1=2" means "epoll_ctl(op=EPOLL_CTL_DEL)")

Remove use of epds in epoll_ctl when op == EPOLL_CTL_DEL.

Fixes: 4d7e30d98939 ("epoll: Add a flag, EPOLLWAKEUP, to prevent suspend while epoll events are ready")
Signed-off-by: Nicolas Iooss <nicolas.iooss_linux at m4x.org>
Cc: Alexander Viro <viro at zeniv.linux.org.uk>
Cc: Arve Hjønnevåg <arve at android.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/eventpoll.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index ead0046..f50d79e 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1852,7 +1852,8 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
 		goto error_tgt_fput;

 	/* Check if EPOLLWAKEUP is allowed */
-	ep_take_care_of_epollwakeup(&epds);
+	if (ep_op_has_event(op))
+		ep_take_care_of_epollwakeup(&epds);

 	/*
 	 * We have to check that the file structure underneath the file descriptor
--
1.9.1