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Mon, 18 May 2026 21:42:27 -0700 (PDT) Date: Tue, 19 May 2026 12:42:19 +0800 From: Ming Lei To: Hongling Zeng Cc: axboe@kernel.dk, ming.lei@canonical.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, zhongling0719@126.com Subject: Re: [PATCH] block/loop: Fix NULL pointer dereference in lo_rw_aio() Message-ID: References: <20260519040103.22776-1-zenghongling@kylinos.cn> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260519040103.22776-1-zenghongling@kylinos.cn> On Tue, May 19, 2026 at 12:01:03PM +0800, Hongling Zeng wrote: > lo->lo_backing_file can be NULL when the loop device is being cleared, > causing NULL pointer dereference in lo_rw_aio(). Add a defensive check > to prevent kernel crash. In v7.1-rc tree, lo->lo_backing_file is cleared in __loop_clr_fd(), which is called from lo_release() only, when it is guaranteed that there isn't inflight IO. So care to share your stack trace? > > Also fix loop_attr_backing_file_show() to use PTR_ERR_OR_ZERO() > for correct NULL pointer handling. > > Fixes: bc07c10a3603a ("block: loop: support DIO & AIO") Can you explain how the issue is introduced in above commit? > Signed-off-by: Hongling Zeng > --- > drivers/block/loop.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c > index 0000913f7efc..d8db1b0d8018 100644 > --- a/drivers/block/loop.c > +++ b/drivers/block/loop.c > @@ -397,6 +397,9 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, > cmd->iocb.ki_flags = 0; > } > > + if (!file) > + return -EIO; If lo->lo_backing_file may become NULL, it isn't enough to add check here only, cause it can be observed in lo_req_flush() & lo_fallocate() too. Thanks, Ming