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

[Dan Aloni]

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@xxxxxxxxxxxxx>

---
commit 8faa94b01e6fd4518b760ce39a2db0ede9444ded
tree c2e3c6ee5f59a4c1e166e4798ddc6e938f448de2
parent c4a1745aa09fc110afdefea0e5d025043e348bae
author Dan Aloni <da-x@xxxxxxxxxxxxx> Tue, 21 Mar 2006 10:19:11 +0200
committer Dan Aloni <da-x@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx, da-x@xxxxxxxxxxx, da-x@xxxxxxx, dan@xxxxxxxxx
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