Commit e904621a authored Aug 04, 2021 by Miklos Szeredi Committed by Greg Kroah-Hartman Sep 22, 2021

fuse: fix use after free in fuse_read_interrupt()



[ 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>

parent a1eaaa6b

fs/fuse/dev.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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);