Re: [syzbot] [fs?] KASAN: slab-use-after-free Read in sys_io_cancel

[Hillf Danton]

On Sat, 02 Mar 2024 23:29:23 -0800
> syzbot found the following issue on:
> 
> HEAD commit:    5ad3cb0ed525 Merge tag 'for-v6.8-rc2' of git://git.kernel...
> git tree:       upstream
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13877412180000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git  master

--- x/fs/aio.c
+++ y/fs/aio.c
@@ -2194,6 +2194,8 @@ SYSCALL_DEFINE3(io_cancel, aio_context_t
 	list_for_each_entry(kiocb, &ctx->active_reqs, ki_list) {
 		if (kiocb->ki_res.obj == obj) {
 			ret = kiocb->ki_cancel(&kiocb->rw);
+			if (ret == 0)
+				refcount_inc(&kiocb->ki_refcnt);
 			list_del_init(&kiocb->ki_list);
 			break;
 		}
@@ -2204,8 +2206,11 @@ SYSCALL_DEFINE3(io_cancel, aio_context_t
 	 * The result argument is no longer used - the io_event is always
 	 * delivered via the ring buffer.
 	 */
-	if (ret == 0 && kiocb->rw.ki_flags & IOCB_AIO_RW)
-		aio_complete_rw(&kiocb->rw, -EINTR);
+	if (ret == 0)
+		if (kiocb->rw.ki_flags & IOCB_AIO_RW)
+			aio_complete_rw(&kiocb->rw, -EINTR);
+		else
+			iocb_put(kiocb);
 
 	percpu_ref_put(&ctx->users);
 
--