[PATCH] fuse: Fix use-after-free in fuse_dev_do_read()

[Kirill Tkhai]

We may pick freed req in this way:

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

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

Reported-by: syzbot+4e975615ca01f2277...@syzkaller.appspotmail.com
Signed-off-by: Kirill Tkhai <ktk...@virtuozzo.com>
---
 fs/fuse/dev.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 11ea2c4a38ab..675caed3e655 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1311,12 +1311,14 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, 
struct file *file,
                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;