[ 3.5.yuz extended stable ] Patch "scsi_debug: Fix off-by-one bug when unmapping region" has been added to staging queue

Herton Ronaldo Krzesinski herton.krzesinski at canonical.com
Thu Nov 15 05:49:30 UTC 2012

This is a note to let you know that I have just added a patch titled

    scsi_debug: Fix off-by-one bug when unmapping region

to the linux-3.5.y-queue branch of the 3.5.yuz extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.yuz tree, see



>From 5ed204a8dd29d2b87e809467adb37f213bcd8582 Mon Sep 17 00:00:00 2001
From: Lukas Czerner <lczerner at redhat.com>
Date: Thu, 16 Aug 2012 16:38:45 +0200
Subject: [PATCH] scsi_debug: Fix off-by-one bug when unmapping region

commit bc977749e967daa56de1922cf4cb38525631c51c upstream.

Currently it is possible to unmap one more block than user requested to
due to the off-by-one error in unmap_region(). This is probably due to
the fact that the end variable despite its name actually points to the
last block to unmap + 1. However in the condition it is handled as the
last block of the region to unmap.

The bug was not previously spotted probably due to the fact that the
region was not zeroed, which has changed with commit
be1dd78de5686c062bb3103f9e86d444a10ed783. With that commit we were able
to corrupt the ext4 file system on 256M scsi_debug device with LBPRZ
enabled using fstrim.

Since the 'end' semantic is the same in several functions there this
commit just fixes the condition to use the 'end' variable correctly in
that context.

Reported-by: Paolo Bonzini <pbonzini at redhat.com>
Signed-off-by: Lukas Czerner <lczerner at redhat.com>
Reviewed-by: Martin K. Petersen <martin.petersen at oracle.com>
Acked-by: Douglas Gilbert <dgilbert at interlog.com>
Signed-off-by: James Bottomley <JBottomley at Parallels.com>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
 drivers/scsi/scsi_debug.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index 182d5a5..f4cc413 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -2054,7 +2054,7 @@ static void unmap_region(sector_t lba, unsigned int len)
 		block = lba + alignment;
 		rem = do_div(block, granularity);

-		if (rem == 0 && lba + granularity <= end && block < map_size) {
+		if (rem == 0 && lba + granularity < end && block < map_size) {
 			clear_bit(block, map_storep);
 			if (scsi_debug_lbprz)
 				memset(fake_storep +

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