[PATCH 4.14 030/124] fuse: Fix use-after-free in fuse_dev_do_read()

Greg Kroah-Hartman
2018-11-19T16:48:10Z

From: Kirill Tkhai <ktkhai@virtuozzo.com>

commit bc78abbd55dd28e2287ec6d6502b842321a17c87 upstream.

We may pick freed req in this way:

[cpu0] [cpu1]
fuse_dev_do_read() fuse_dev_do_write()
list_move_tail(&req->list, ...); ...
spin_unlock(&fpq->lock); ...
... request_end(fc, req);
... fuse_put_request(fc, req);
if (test_bit(FR_INTERRUPTED, ...))
queue_interrupt(fiq, req);

Fix that by keeping req alive until we finish all manipulations.

Reported-by: syzbot+4e975615ca01f2277bdd@syzkaller.appspotmail.com
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: 46c34a348b0a ("fuse: no fc->lock for pqueue parts")
Cc: <stable@vger.kernel.org> # v4.2
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/fuse/dev.c | 2 ++
1 file changed, 2 insertions(+)

--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1309,12 +1309,14 @@ static ssize_t fuse_dev_do_read(struct f
goto out_end;
}
list_move_tail(&req->list, &fpq->processing);
+ __fuse_get_request(req);
spin_unlock(&fpq->lock);
set_bit(FR_SENT, &req->flags);
/* matches barrier in request_wait_answer() */
smp_mb__after_atomic();
if (test_bit(FR_INTERRUPTED, &req->flags))
queue_interrupt(fiq, req);
+ fuse_put_request(fc, req);

return reqsize;