fuse: fix use after free in fuse_read_interrupt()

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>

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 1c8f79b..dde341a 100644 (file)
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -288,10 +288,10 @@ void fuse_request_end(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);