From 4c90b76e0198deb89376988daa8d96b48bea7fcf Mon Sep 17 00:00:00 2001 From: Zhihao Cheng Date: Tue, 22 Sep 2026 11:05:38 +0800 Subject: [PATCH] md: Fix the null-ptr-deref of 'mddev->private' while submitting IO Concurrent processes md_stop and IO submission can trigger a NULL pointer dereference of mddev->private: BUG: kernel NULL pointer dereference, address: 0000000000000070 RIP: 0010:_wait_barrier+0x2f/0x250 Call Trace: raid1_make_request+0x150/0xf50 md_handle_request+0x104/0x530 md_submit_bio+0x76/0x130 submit_bio+0xdd/0x250 submit_bio_wait+0x1f/0x40 __blkdev_direct_IO_simple+0x1f6/0x370 blkdev_write_iter+0x3b2/0x520 ksys_write+0x7d/0x190 One process can submit I/O through an open file while a forked process uses the same file to issue STOP_ARRAY. The opener check permits this because md_open() was called only once. do_md_stop() can then clear mddev->private while the I/O is entering the personality make_request callback. This affects raid0, raid1, raid10, and raid5. Suspend STOP_ARRAY while holding the reconfiguration lock so teardown waits for active_io references to drain. Fail I/O in md_handle_request() if mddev->pers is NULL after the array resumes. The sysfs stopping paths are protected by mddev_set_closing_and_sync_blockdev(). Apply that protection to both clear and inactive transitions even when the array is read-only. dm-raid teardown is already invoked with the device suspended. Fetch a reproducer in https://bugzilla.kernel.org/show_bug.cgi?id=222020 Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: syzbot+3fe892ea5fc292e1353f@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3fe892ea5fc292e1353f Signed-off-by: Zhihao Cheng Link: https://patch.msgid.link/20260922030538.1634904-1-chengzhihao1@huawei.com Signed-off-by: Yu Kuai --- drivers/md/md.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/drivers/md/md.c b/drivers/md/md.c index 0f7115b31ca3..118de338266a 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -414,6 +414,20 @@ bool md_handle_request(struct mddev *mddev, struct bio *bio) if (!percpu_ref_tryget_live(&mddev->active_io)) goto check_suspended; } + if (!mddev->pers) { + /* + * The __md_stop() sets 'mddev->private' to NULL during + * the IO submitting, check 'mddev->pers' before the IO + * being processed by specific driver to avoid the + * null-ptr-deref of 'mddev->'. The check is + * safe because the IO has got the 'mddev->active_io' + * reference, and all __md_stop() callers will wait for + * the reference to be zero. + */ + bio_io_error(bio); + percpu_ref_put(&mddev->active_io); + return true; + } if (!mddev->pers->make_request(mddev, bio)) { percpu_ref_put(&mddev->active_io); if (mddev_is_dm(mddev) && mddev->pers->prepare_suspend) @@ -4670,7 +4684,8 @@ array_state_store(struct mddev *mddev, const char *buf, size_t len) case readonly: case inactive: case read_auto: - if (!mddev->pers || !md_is_rdwr(mddev)) + if (!mddev->pers || + (st != clear && st != inactive && !md_is_rdwr(mddev))) break; /* write sysfs will not open mddev and opener should be 0 */ err = mddev_set_closing_and_sync_blockdev(mddev, 0); @@ -8299,6 +8314,7 @@ static bool md_ioctl_need_suspend(unsigned int cmd) case HOT_REMOVE_DISK: case SET_BITMAP_FILE: case SET_ARRAY_INFO: + case STOP_ARRAY: return true; default: return false;