From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755331AbXKZL2y (ORCPT ); Mon, 26 Nov 2007 06:28:54 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753639AbXKZL2q (ORCPT ); Mon, 26 Nov 2007 06:28:46 -0500 Received: from nz-out-0506.google.com ([64.233.162.226]:34165 "EHLO nz-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753225AbXKZL2p (ORCPT ); Mon, 26 Nov 2007 06:28:45 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=received:date:from:to:subject:message-id:mime-version:content-type:content-disposition:user-agent; b=wWESFyLXFbLQ5blqKihpuePtDZRzfbS4Dip7F73pl2EYOWHyyUQnc2g6Ux1hKVcFTSfNcYyeJTF23lpZdD+2fRrGCxDzhj/nmsKuV5Qupww9pcLz/COBRoeVCvPnx7A+l/f5i1dRT9NG5wKTShekvd/oOu0no8PJIQ0kxaTb+Gg= Date: Mon, 26 Nov 2007 20:28:32 +0900 From: Tejun Heo To: jens.axboe@oracle.com, linux-kernel@vger.kernel.org Subject: [PATCH] scatterlist: add more safeguards Message-ID: <20071126112832.GA9232@htj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.16 (2007-06-09) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Add more safeguards to protect against misinterpreting a chain entry as a normal scatterlist and vice-versa. * Make sure the entry isn't a chain when assigning and reading a normal sg. * Clear offset and length when chaining. Signed-off-by: Tejun Heo --- While converting libata to use chained-sg, I felt a bit insecure and added a few more safe guards. Feel free to include or ignore them. Thanks. include/linux/scatterlist.h | 37 ++++++++++++++++++++++++++----------- 1 file changed, 26 insertions(+), 11 deletions(-) Index: work/include/linux/scatterlist.h =================================================================== --- work.orig/include/linux/scatterlist.h +++ work/include/linux/scatterlist.h @@ -26,6 +26,16 @@ #define SG_MAGIC 0x87654321 +/* + * We overload the LSB of the page pointer to indicate whether it's + * a valid sg entry, or whether it points to the start of a new scatterlist. + * Those low bits are there for everyone! (thanks mason :-) + */ +#define sg_is_chain(sg) ((sg)->page_link & 0x01) +#define sg_is_last(sg) ((sg)->page_link & 0x02) +#define sg_chain_ptr(sg) \ + ((struct scatterlist *) ((sg)->page_link & ~0x03)) + /** * sg_assign_page - Assign a given page to an SG entry * @sg: SG entry @@ -47,6 +57,7 @@ static inline void sg_assign_page(struct BUG_ON((unsigned long) page & 0x03); #ifdef CONFIG_DEBUG_SG BUG_ON(sg->sg_magic != SG_MAGIC); + BUG_ON(sg_is_chain(sg)); #endif sg->page_link = page_link | (unsigned long) page; } @@ -73,7 +84,14 @@ static inline void sg_set_page(struct sc sg->length = len; } -#define sg_page(sg) ((struct page *) ((sg)->page_link & ~0x3)) +static inline struct page *sg_page(struct scatterlist *sg) +{ +#ifdef CONFIG_DEBUG_SG + BUG_ON(sg->sg_magic != SG_MAGIC); + BUG_ON(sg_is_chain(sg)); +#endif + return (struct page *)((sg)->page_link & ~0x3); +} /** * sg_set_buf - Set sg entry to point at given data @@ -88,16 +106,6 @@ static inline void sg_set_buf(struct sca sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf)); } -/* - * We overload the LSB of the page pointer to indicate whether it's - * a valid sg entry, or whether it points to the start of a new scatterlist. - * Those low bits are there for everyone! (thanks mason :-) - */ -#define sg_is_chain(sg) ((sg)->page_link & 0x01) -#define sg_is_last(sg) ((sg)->page_link & 0x02) -#define sg_chain_ptr(sg) \ - ((struct scatterlist *) ((sg)->page_link & ~0x03)) - /** * sg_next - return the next scatterlist entry in a list * @sg: The current sg entry @@ -179,6 +187,13 @@ static inline void sg_chain(struct scatt #ifndef ARCH_HAS_SG_CHAIN BUG(); #endif + + /* + * offset and length are unused for chain entry. Clear them. + */ + prv->offset = 0; + prv->length = 0; + /* * Set lowest bit to indicate a link pointer, and make sure to clear * the termination bit if it happens to be set.