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Subject: [PATCH] fuse: Fix use-after-free in fuse_dev_do_write()
From:   Kirill Tkhai <ktkhai@virtuozzo.com>
To:     miklos@szeredi.hu, dvyukov@google.com,
        syzbot+4e975615ca01f2277bdd@syzkaller.appspotmail.com,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        ktkhai@virtuozzo.com
Date:   Tue, 25 Sep 2018 12:52:42 +0300
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After we found req in request_find() and released the lock,
everything may happen with the req in parallel.

Keep it alive till we finish touch its memory.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
 fs/fuse/dev.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 675caed3e655..c2af8042f176 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1877,16 +1877,20 @@ static ssize_t fuse_dev_do_write(struct fuse_dev *fud,
 
 	/* Is it an interrupt reply? */
 	if (req->intr_unique == oh.unique) {
+		__fuse_get_request(req);
 		spin_unlock(&fpq->lock);
 
 		err = -EINVAL;
-		if (nbytes != sizeof(struct fuse_out_header))
+		if (nbytes != sizeof(struct fuse_out_header)) {
+			fuse_put_request(fc, req);
 			goto err_finish;
+		}
 
 		if (oh.error == -ENOSYS)
 			fc->no_interrupt = 1;
 		else if (oh.error == -EAGAIN)
 			queue_interrupt(&fc->iq, req);
+		fuse_put_request(fc, req);
 
 		fuse_copy_finish(cs);
 		return nbytes;