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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, lijiazi <lijiazi@xiaomi.com>,
        Miklos Szeredi <mszeredi@redhat.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.4 236/260] fuse: fix use after free in fuse_read_interrupt()
Date:   Mon, 20 Sep 2021 18:44:14 +0200
Message-Id: <20210920163939.145541437@linuxfoundation.org>
In-Reply-To: <20210920163931.123590023@linuxfoundation.org>
References: <20210920163931.123590023@linuxfoundation.org>
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From: Miklos Szeredi <mszeredi@redhat.com>

[ Upstream commit e1e71c168813564be0f6ea3d6740a059ca42d177 ]

There is a potential race between fuse_read_interrupt() and
fuse_request_end().

TASK1
  in fuse_read_interrupt(): delete req->intr_entry (while holding
  fiq->lock)

TASK2
  in fuse_request_end(): req->intr_entry is empty -> skip fiq->lock
  wake up TASK3

TASK3
  request is freed

TASK1
  in fuse_read_interrupt(): dereference req->in.h.unique ***BAM***

Fix by always grabbing fiq->lock if the request was ever interrupted
(FR_INTERRUPTED set) thereby serializing with concurrent
fuse_read_interrupt() calls.

FR_INTERRUPTED is set before the request is queued on fiq->interrupts.
Dequeing the request is done with list_del_init() but FR_INTERRUPTED is not
cleared in this case.

Reported-by: lijiazi <lijiazi@xiaomi.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/fuse/dev.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 16aa55b73ccf..7205a89fbb5f 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -282,10 +282,10 @@ void fuse_request_end(struct fuse_conn *fc, struct fuse_req *req)
 
 	/*
 	 * test_and_set_bit() implies smp_mb() between bit
-	 * changing and below intr_entry check. Pairs with
+	 * changing and below FR_INTERRUPTED check. Pairs with
 	 * smp_mb() from queue_interrupt().
 	 */
-	if (!list_empty(&req->intr_entry)) {
+	if (test_bit(FR_INTERRUPTED, &req->flags)) {
 		spin_lock(&fiq->lock);
 		list_del_init(&req->intr_entry);
 		spin_unlock(&fiq->lock);
-- 
2.30.2