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From: Hillf Danton <hdanton@sina.com>
To: syzbot <syzbot+b91eb2ed18f599dd3c31@syzkaller.appspotmail.com>
Cc: linux-kernel@vger.kernel.org,
	syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [fs?] KASAN: slab-use-after-free Read in sys_io_cancel
Date: Mon,  4 Mar 2024 22:07:02 +0800
Message-Id: <20240304140702.1457-1-hdanton@sina.com>
In-Reply-To: <0000000000006945730612bc9173@google.com>
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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);
 
--