This is a note to let you know that I've just added the patch titled fuse: fix use after free in fuse_read_interrupt() to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: fuse-fix-use-after-free-in-fuse_read_interrupt.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 6e0c71a3561ccece64997547ae6563bd5f30b0ce Author: Miklos Szeredi <mszeredi@xxxxxxxxxx> Date: Wed Aug 4 13:22:58 2021 +0200 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@xxxxxxxxxx> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c index 16aa55b73ccf..7205a89fbb5f 100644 --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -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);