linux-kernel - [PATCH] fs,eventpoll: Don't test for bitfield with stack value

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Date:   Tue, 14 Feb 2017 18:49:35 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     LINUXFS-ML <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...uxfoundation.org>,
        Andrey Vagin <avagin@...tuozzo.com>
Subject: [PATCH] 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.

Signed-off-by: Cyrill Gorcunov <gorcunov@...il.com>
---
 fs/eventpoll.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-ml.git/fs/eventpoll.c
===================================================================
--- linux-ml.git.orig/fs/eventpoll.c
+++ linux-ml.git/fs/eventpoll.c
@@ -1895,7 +1895,7 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, in
 	 * 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) ||