Re: [syzbot] KASAN: use-after-free Write in expire_timers

[Yu Liao]

On 2022/11/22 2:35, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    b6e7fdfd6f6a Merge tag 'iommu-fixes-v6.1-rc5' of git://git..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11c28f95880000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=95fb379f123ba8ce
> dashboard link: https://syzkaller.appspot.com/bug?extid=38ee3533e07da8749f85
> compiler:       aarch64-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> userspace arch: arm64

Fix data race between virtual_ncidev_close() and virtual_ncidev_open().

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
b6e7fdfd6f6a

--- a/drivers/nfc/virtual_ncidev.c
+++ b/drivers/nfc/virtual_ncidev.c
@@ -161,12 +161,8 @@ static int virtual_ncidev_close(struct inode *inode,
struct file *file)

    if (state == virtual_ncidev_enabled) {
        state = virtual_ncidev_disabling;
-       mutex_unlock(&nci_mutex);
-
        nci_unregister_device(ndev);
        nci_free_device(ndev);
-
-       mutex_lock(&nci_mutex);
    }

    state = virtual_ncidev_disabled;
--