[Xen-changelog] [xen-unstable] [BLOCK] blkback: Fix first_sect check.

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User kfraser@xxxxxxxxxxxxxxxxxxxxx
# Node ID d2ba4ac3616895f7260f108b9d5c3c487be8d482
# Parent  f326ec66e5149c0140a671fe47e4a75437897d7a
[BLOCK] blkback: Fix first_sect check.

The blkback code checks first_sect by computing last_sect - first_sect
+ 1. If this is not positive then the request is
rejected. Unfortunately, the calculation is stored in an unsigned
integer before the check is made so negative values will not be
rejected.

This patch fixes this by explicitly comparing first_sect with
last_sect.

The blktap code is similar but it stores the difference in a signed
integer so it's okay.

Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
---
 linux-2.6-xen-sparse/drivers/xen/blkback/blkback.c |    2 +-
 1 files changed, 1 insertion(+), 1 deletion(-)

diff -r f326ec66e514 -r d2ba4ac36168 
linux-2.6-xen-sparse/drivers/xen/blkback/blkback.c
--- a/linux-2.6-xen-sparse/drivers/xen/blkback/blkback.c        Mon Oct 23 
10:00:14 2006 +0100
+++ b/linux-2.6-xen-sparse/drivers/xen/blkback/blkback.c        Mon Oct 23 
10:05:32 2006 +0100
@@ -375,7 +375,7 @@ static void dispatch_rw_block_io(blkif_t
                        req->seg[i].first_sect + 1;
 
                if ((req->seg[i].last_sect >= (PAGE_SIZE >> 9)) ||
-                   (seg[i].nsec <= 0))
+                   (req->seg[i].last_sect < req->seg[i].first_sect))
                        goto fail_response;
                preq.nr_sects += seg[i].nsec;
 

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