fuse: re-lock request before replacing page cache folio

commit a078484 upstream.

fuse_try_move_folio() unlocks the request on entry but does not
re-lock it on the success path. This means fuse_chan_abort() can end the
request and free the fuse_io_args (eg fuse_readpages_end()) while the
subsequent copy chain logic after fuse_try_move_folio() accesses the
fuse_io_args, leading to use-after-free issues.

Fix this by calling lock_request() before replace_page_cache_folio().
This ensures the request is locked on the success path which will
prevent the fuse_io_args from being freed while the later copying logic
runs, and also ensures that the ap->folios[i]->mapping is never null
since ap->folios[i] will always point to the newfolio after
replace_page_cache_folio().

Fixes: ce534fb ("fuse: allow splice to move pages")
Cc: stable@vger.kernel.org
Reported-by: Lei Lu <llfamsec@gmail.com>
Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: joannekoong

fs/fuse/dev.c

@@ -1037,6 +1037,10 @@ static int fuse_try_move_folio(struct fuse_copy_state *cs, struct folio **foliop
 	if (WARN_ON(folio_test_mlocked(oldfolio)))
 		goto out_fallback_unlock;
 
+	err = lock_request(cs->req);
+	if (err)
+		goto out_fallback_unlock;
+
 	replace_page_cache_folio(oldfolio, newfolio);
 
 	folio_get(newfolio);
@@ -1050,20 +1054,7 @@ static int fuse_try_move_folio(struct fuse_copy_state *cs, struct folio **foliop
 	 */
 	pipe_buf_release(cs->pipe, buf);
 
-	err = 0;
-	spin_lock(&cs->req->waitq.lock);
-	if (test_bit(FR_ABORTED, &cs->req->flags))
-		err = -ENOENT;
-	else
-		*foliop = newfolio;
-	spin_unlock(&cs->req->waitq.lock);
-
-	if (err) {
-		folio_unlock(newfolio);
-		folio_put(newfolio);
-		goto out_put_old;
-	}
-
+	*foliop = newfolio;
 	folio_unlock(oldfolio);
 	/* Drop ref for ap->pages[] array */
 	folio_put(oldfolio);