Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754609AbaAVHBx (ORCPT ); Wed, 22 Jan 2014 02:01:53 -0500 Received: from e28smtp02.in.ibm.com ([122.248.162.2]:56692 "EHLO e28smtp02.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753955AbaAVHBw (ORCPT ); Wed, 22 Jan 2014 02:01:52 -0500 Message-ID: <52DF6AA1.4080708@linux.vnet.ibm.com> Date: Wed, 22 Jan 2014 12:22:17 +0530 From: Raghavendra K T Organization: IBM User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 MIME-Version: 1.0 To: Andrew Morton CC: Alexander Viro , Matias Bjorling , Jens Axboe , Yuanhan Liu , "Darrick J. Wong" , Jan Kara , Johannes Weiner , Zhang Yanfei , Jeff , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Sumanth Subject: Re: [RFC PATCH V3 2/2] fs : Add sanity checks for block size > PAGE_SIZE References: <1390303800-22422-1-git-send-email-raghavendra.kt@linux.vnet.ibm.com> <1390303800-22422-3-git-send-email-raghavendra.kt@linux.vnet.ibm.com> <20140121122110.4a74f04f43d2fdc0a8ae35bf@linux-foundation.org> In-Reply-To: <20140121122110.4a74f04f43d2fdc0a8ae35bf@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14012207-5816-0000-0000-00000BE26112 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/22/2014 01:51 AM, Andrew Morton wrote: > On Tue, 21 Jan 2014 17:00:00 +0530 Raghavendra K T wrote: > >> We could hit null pointer dereference error during alloc_page_buffers >> in : (1) block size > PAGE_SIZE (2) low memory. >> Add sanity check for that. >> >> Signed-off-by: Raghavendra K T >> --- >> fs/block_dev.c | 1 + >> fs/buffer.c | 6 ++++++ >> 2 files changed, 7 insertions(+) >> >> diff --git a/fs/block_dev.c b/fs/block_dev.c >> index 1e86823..2481d42 100644 >> --- a/fs/block_dev.c >> +++ b/fs/block_dev.c >> @@ -1027,6 +1027,7 @@ void bd_set_size(struct block_device *bdev, loff_t size) >> break; >> bsize <<= 1; >> } >> + BUG_ON(bsize > PAGE_SIZE); >> bdev->bd_block_size = bsize; >> bdev->bd_inode->i_blkbits = blksize_bits(bsize); >> } > > alloc_page_buffers() will always return NULL if passed size >= > PAGE_SIZE. So if we're going to add a check, it would be better to add > it to alloc_page_buffers() because that will catch errors from the > widest range of callsites. In that case how about converting BUG_ON to setting a default value of PAGE_SIZE for bs in bd_set_size() itself (with a warning)? > > But alloc_page_buffers() is pretty frequently called and I'd be > inclined to not add any check - most callers will just go oops and that > will provide basically the same information. Agree with this concern. > >> --- a/fs/buffer.c >> +++ b/fs/buffer.c >> @@ -1571,6 +1571,12 @@ void create_empty_buffers(struct page *page, >> struct buffer_head *bh, *head, *tail; >> >> head = alloc_page_buffers(page, blocksize, 1); >> + >> + /* >> + * alloc_page_buffers() could return NULL on (1) bs > PAGE_SIZE >> + * (2) low memory case. Ensure that we don't dereference null ptr >> + */ >> + BUG_ON(!head); > > This is unneeded. > > - bs > PAGE_SIZE can be checked elsewhere in a direct fashion > > - low memory case can't happen - we passed retry=1 > > - create_empty_buffers() will immediately go oops if head==NULL. > That oops contains the same info as is presented by a BUG(). Okay. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/