Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752608AbaAUUVO (ORCPT ); Tue, 21 Jan 2014 15:21:14 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:44244 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751191AbaAUUVM (ORCPT ); Tue, 21 Jan 2014 15:21:12 -0500 Date: Tue, 21 Jan 2014 12:21:10 -0800 From: Andrew Morton To: Raghavendra K T 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 Message-Id: <20140121122110.4a74f04f43d2fdc0a8ae35bf@linux-foundation.org> In-Reply-To: <1390303800-22422-3-git-send-email-raghavendra.kt@linux.vnet.ibm.com> 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> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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. > --- 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(). -- 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/