fs,eventpoll: don't test for bitfield with stack value

In case if epoll_ctl is called with operation EPOLL_CTL_DEL then
@epds.events variable allocated on stack may contain random bits which
we test then for EPOLLEXCLUSIVE.  Since currently the test look like

	if (epds.events & EPOLLEXCLUSIVE) {
		if (op == EPOLL_CTL_MOD)
			goto error_tgt_fput;
		if (op == EPOLL_CTL_ADD && (is_file_epoll(tf.file) ||
				(epds.events & ~EPOLLEXCLUSIVE_OK_BITS)))
			goto error_tgt_fput;
	}

Nothing serious will happen even if epds.events has this bit set, still
better to be on safe side and make sure that we're to test this bit at
all.

Link: http://lkml.kernel.org/r/20170214154935.GG1850@uranus.lan
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrey Vagin <avagin@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index bcb68fcc844515c67e7efc83710dabdce361f8b9..5ec16313da1a1cc59f462038f331f50c35f8b89d 100644 (file)
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1895,7 +1895,7 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
         * so EPOLLEXCLUSIVE is not allowed for a EPOLL_CTL_MOD operation.
         * Also, we do not currently supported nested exclusive wakeups.
         */
-       if (epds.events & EPOLLEXCLUSIVE) {
+       if (ep_op_has_event(op) && (epds.events & EPOLLEXCLUSIVE)) {
                if (op == EPOLL_CTL_MOD)
                        goto error_tgt_fput;
                if (op == EPOLL_CTL_ADD && (is_file_epoll(tf.file) ||