target_core_sbc's compare_and_write functionality suffers from taking
data at the wrong memory location when writing a CAW request to disk.
Given the following sample LIO subtopology,
% targetcli ls /loopback/
o- loopback ................................. [1 Target]
o- naa.6001405ebb8df14a ....... [naa.60014059143ed2b3]
o- luns ................................... [2 LUNs]
o- lun0 ................ [iblock/ram0 (/dev/ram0)]
o- lun1 ................ [iblock/ram1 (/dev/ram1)]
% lsscsi -g
[3:0:1:0] disk LIO-ORG IBLOCK 4.0 /dev/sdc /dev/sg3
[3:0:1:1] disk LIO-ORG IBLOCK 4.0 /dev/sdd /dev/sg4
the following bug can be observed in Linux 4.3 and 4.4~rc1:
% perl -e 'print chr$_ for 0..255,reverse 0..255' >rand
% perl -e 'print "\0" x 512' >zero
% cat rand >/dev/sdd
% sg_compare_and_write -i rand -D zero --lba 0 /dev/sdd
% sg_compare_and_write -i zero -D rand --lba 0 /dev/sdd
Miscompare reported
% hexdump -Cn 512 /dev/sdd
00000000 0f 0e 0d 0c 0b 0a 09 08 07 06 05 04 03 02 01 00
00000010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
*
00000200
Rather than writing all-zeroes as instructed with the -D file, it
corrupts the data in the sector by splicing some of the original
bytes in. The page of the first entry of cmd->t_data_sg includes the
CDB, and sg->offset is set to a position past the CDB. I presume that
sg->offset is also the right choice to use for subsequent sglist
members.
Signed-off-by: Jan Engelhardt <jengelh@xxxxxxxxxxxx>
---
The following changes since commit 8005c49d9aea74d382f474ce11afbbc7d7130bec:
Linux 4.4-rc1 (2015-11-15 17:00:27 -0800)
are available in the git repository at:
git://git.inai.de/linux tcm
for you to fetch changes up to 54d035e8349bdb547a4372ebe6a83710971052bb:
target: fix a case of data corruption during COMPARE_AND_WRITE
drivers/target/target_core_sbc.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/target/target_core_sbc.c b/drivers/target/target_core_sbc.c
index 0b4b2a6..dc51cdc 100644
--- a/drivers/target/target_core_sbc.c
+++ b/drivers/target/target_core_sbc.c
@@ -556,11 +556,11 @@ static sense_reason_t compare_and_write_callback(struct se_cmd *cmd, bool succes
if (block_size < PAGE_SIZE) {
sg_set_page(&write_sg[i], m.page, block_size,
- block_size);
+ m.piter.sg->offset + block_size);
} else {
sg_miter_next(&m);
sg_set_page(&write_sg[i], m.page, block_size,
- 0);
+ m.piter.sg->offset);
}
len -= block_size;
i++;
--
2.4.3
--
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