linux-kernel - [PATCH AUTOSEL 4.9 1/2] epoll: do not insert into poll queues until all sanity checks are done

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Message-Id: <20201005144531.2527844-1-sashal@kernel.org>
Date:   Mon,  5 Oct 2020 10:45:30 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Al Viro <viro@...iv.linux.org.uk>, Sasha Levin <sashal@...nel.org>,
        linux-fsdevel@...r.kernel.org
Subject: [PATCH AUTOSEL 4.9 1/2] epoll: do not insert into poll queues until all sanity checks are done

From: Al Viro <viro@...iv.linux.org.uk>

[ Upstream commit f8d4f44df056c5b504b0d49683fb7279218fd207 ]

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/eventpoll.c | 37 ++++++++++++++++++-------------------
 1 file changed, 18 insertions(+), 19 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 8c40d6652a9a9..d5b68ebbb1631 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1332,6 +1332,22 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
 		RCU_INIT_POINTER(epi->ws, NULL);
 	}
 
+	/* Add the current item to the list of active epoll hook for this file */
+	spin_lock(&tfile->f_lock);
+	list_add_tail_rcu(&epi->fllink, &tfile->f_ep_links);
+	spin_unlock(&tfile->f_lock);
+
+	/*
+	 * Add the current item to the RB tree. All RB tree operations are
+	 * protected by "mtx", and ep_insert() is called with "mtx" held.
+	 */
+	ep_rbtree_insert(ep, epi);
+
+	/* now check if we've created too many backpaths */
+	error = -EINVAL;
+	if (full_check && reverse_path_check())
+		goto error_remove_epi;
+
 	/* Initialize the poll table using the queue callback */
 	epq.epi = epi;
 	init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);
@@ -1354,22 +1370,6 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
 	if (epi->nwait < 0)
 		goto error_unregister;
 
-	/* Add the current item to the list of active epoll hook for this file */
-	spin_lock(&tfile->f_lock);
-	list_add_tail_rcu(&epi->fllink, &tfile->f_ep_links);
-	spin_unlock(&tfile->f_lock);
-
-	/*
-	 * Add the current item to the RB tree. All RB tree operations are
-	 * protected by "mtx", and ep_insert() is called with "mtx" held.
-	 */
-	ep_rbtree_insert(ep, epi);
-
-	/* now check if we've created too many backpaths */
-	error = -EINVAL;
-	if (full_check && reverse_path_check())
-		goto error_remove_epi;
-
 	/* We have to drop the new item inside our item list to keep track of it */
 	spin_lock_irqsave(&ep->lock, flags);
 
@@ -1395,6 +1395,8 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
 
 	return 0;
 
+error_unregister:
+	ep_unregister_pollwait(ep, epi);
 error_remove_epi:
 	spin_lock(&tfile->f_lock);
 	list_del_rcu(&epi->fllink);
@@ -1402,9 +1404,6 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
 
 	rb_erase(&epi->rbn, &ep->rbr);
 
-error_unregister:
-	ep_unregister_pollwait(ep, epi);
-
 	/*
 	 * We need to do this because an event could have been arrived on some
 	 * allocated wait queue. Note that we don't care about the ep->ovflist
-- 
2.25.1