[PATCH] scsi: properly count the number of pages in scsi_req_map_sg()

Dan Aloni
2006-03-21T08:37:45Z

Improper calculation of the number of pages causes bio_alloc() to
be called with nr_iovecs=0, and slab corruption later.

For example, a simple scatterlist that fails: {(3644,452), (0, 60)},
(offset, size). bufflen=512 => nr_pages=1 => breakage. The proper
page count for this example is 2.

Signed-off-by: Dan Aloni <da-x@monatomic.org>

---
commit 8faa94b01e6fd4518b760ce39a2db0ede9444ded
tree c2e3c6ee5f59a4c1e166e4798ddc6e938f448de2
parent c4a1745aa09fc110afdefea0e5d025043e348bae
author Dan Aloni <da-x@monatomic.org> Tue, 21 Mar 2006 10:19:11 +0200
committer Dan Aloni <da-x@monatomic.org> Tue, 21 Mar 2006 10:19:11 +0200

drivers/scsi/scsi_lib.c | 9 ++++++++-
1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 701a328..a42f3aa 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -368,13 +368,20 @@ static int scsi_req_map_sg(struct reques
int nsegs, unsigned bufflen, gfp_t gfp)
{
struct request_queue *q = rq->q;
- int nr_pages = (bufflen + PAGE_SIZE - 1) >> PAGE_SHIFT;
+ int nr_pages = 0;
unsigned int data_len = 0, len, bytes, off;
struct page *page;
struct bio *bio = NULL;
int i, err, nr_vecs = 0;

for (i = 0; i < nsegs; i++) {
+ off = sgl[i].offset;
+ len = sgl[i].length;
+
+ nr_pages += ((off + len + PAGE_SIZE - 1) >> PAGE_SHIFT) - (off >> PAGE_SHIFT);
+ }
+
+ for (i = 0; i < nsegs; i++) {
page = sgl[i].page;
off = sgl[i].offset;
len = sgl[i].length;

--
Dan Aloni
da-x@monatomic.org, da-x@colinux.org, da-x@gmx.net, dan@xiv.co.il