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@xxxxxxx>
---
fs/eventpoll.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index b10b48c..7bcfff9 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
--
1.7.10.4
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