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Fri, 18 Sep 2026 00:29:25 -0700 (PDT) From: Abd-Alrhman Masalkhi To: Zhihao Cheng , song@kernel.org, yukuai@fygo.io, xiao@kernel.org, magiclinan@didiglobal.com, eadavis@sina.com Cc: linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org, chengzhihao1@huawei.com, yangerkun@huawei.com, yi.zhang@huawei.com Subject: Re: [PATCH v3] md: Fix the null-ptr-deref of 'mddev->private' while submitting IO In-Reply-To: <20260918070900.1945351-1-chengzhihao1@huawei.com> References: <20260918070900.1945351-1-chengzhihao1@huawei.com> Date: Fri, 18 Sep 2026 09:29:23 +0200 Message-ID: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Hi Zhihao, On Fri, Sep 18, 2026 at 15:09 +0800, Zhihao Cheng wrote: > Concurrent processes md_stop and IO submitting could trigger a > null-ptr-deref 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 > > P1 > fd = open(/dev/md0, O_RDWR) > P2 (forked from P1, fd' <= fd) > write(fd) > submit_bio > md_handle_request > raid1_make_request > raid1_write_request > ioctl(fd, STOP_ARRAY) > mddev_set_closing_and_sync_blockdev > // check passed, mddev->openers = 1, > // because md_open() is only called > // once in P1->open > do_md_stop > __md_stop > mddev->private = NULL > > conf = mddev->private // NULL > wait_barrier(conf, sector) // null-ptr-deref ! > > It is a common problem for raid0/1/10/5, and __md_stop could be triggered > by several paths(eg. ioctl, sysfs, ->dtr). Fix it by replacing > mddev_lock() with mddev_suspend_and_lock() for all __md_stop() callers. > The caller dm_table_destroy() is guaranteed being invoked with device > suspended, so raid_dtr() could keep using mddev_lock_nointr(). > The caller array_state_store() is guaranteed by the check > mddev_set_closing_and_sync_blockdev(mddev, 0). For example, someone open > /dev/mdx, write something and close /dev/mdx, it won't trigger the > problem, all dirty pages can be flushed before mddev->openers decrement. > Besides, fail the submitting IO in md_handle_request() if the > 'mddev->pers' becomes NULL. > > 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 > --- > v1->v2: > 1. Add 'mddev->pers != NULL' check before make_request > 2. Delete dm-raid caller(->dtr) modifications > 3. Move memalloc_noio_restore after mddev_unlock_and_resume > v2->v3: > 1. Remove modifications in array_state_store() > 2. update commit msg > drivers/md/md.c | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/drivers/md/md.c b/drivers/md/md.c > index 680b34a63cb3..e73338c26d53 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) { Isn't this case already handled by md_submit_bio(). take a look in md_submit_bio() > + /* > + * 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) > @@ -8299,6 +8313,7 @@ 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; > -- > 2.52.0 > -- Best Regards, Abd-Alrhman