Overview
About vulnerability
In the Linux kernel, the following vulnerability has been resolved:
dm cache: fix out-of-bounds access to the dirty bitset when resizing
dm-cache checks the dirty bits of the cache blocks to be dropped when shrinking the fast device, but an index bug in bitset iteration causes out-of-bounds access.
Reproduce steps:
- create a cache device of 1024 cache blocks (128 bytes dirty bitset)
dmsetup create cmeta –table “0 8192 linear /dev/sdc 0”
dmsetup create cdata –table “0 131072 linear /dev/sdc 8192”
dmsetup create corig –table “0 524288 linear /dev/sdc 262144”
dd if=/dev/zero of=/dev/mapper/cmeta bs=4k count=1 oflag=direct
dmsetup create cache –table “0 524288 cache /dev/mapper/cmeta
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0”
- shrink the fast device to 512 cache blocks, triggering out-of-bounds access to the dirty bitset (offset 0x80)
dmsetup suspend cache dmsetup reload cdata –table “0 65536 linear /dev/sdc 8192” dmsetup resume cdata dmsetup resume cache
KASAN reports:
BUG: KASAN: vmalloc-out-of-bounds in cache_preresume+0x269/0x7b0 Read of size 8 at addr ffffc900000f3080 by task dmsetup/131
(…snip…) The buggy address belongs to the virtual mapping at [ffffc900000f3000, ffffc900000f5000) created by: cache_ctr+0x176a/0x35f0
(…snip…) Memory state around the buggy address: ffffc900000f2f80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ffffc900000f3000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffffc900000f3080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ^ ffffc900000f3100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ffffc900000f3180: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
Fix by making the index post-incremented.
Details
- Affected product:
- AlmaLinux 9.2 ESU , CentOS 8.4 ELS , CentOS 8.5 ELS , CentOS Stream 8 ELS , Oracle Linux 7 ELS , Ubuntu 16.04 ELS , Ubuntu 18.04 ELS
- Affected packages:
- linux-hwe @ 4.15.0 (+8 more)
In the Linux kernel, the following vulnerability has been resolved:
dm cache: fix out-of-bounds access to the dirty bitset when resizing
dm-cache checks the dirty bits of the cache blocks to be dropped when shrinking the fast device, but an index bug in bitset iteration causes out-of-bounds access.
Reproduce steps:
- create a cache device of 1024 cache blocks (128 bytes dirty bitset)
dmsetup create cmeta –table “0 8192 linear /dev/sdc 0”
dmsetup create cdata –table “0 131072 linear /dev/sdc 8192”
dmsetup create corig –table “0 524288 linear /dev/sdc 262144”
dd if=/dev/zero of=/dev/mapper/cmeta bs=4k count=1 oflag=direct
dmsetup create cache –table “0 524288 cache /dev/mapper/cmeta
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0”
- shrink the fast device to 512 cache blocks, triggering out-of-bounds access to the dirty bitset (offset 0x80)
dmsetup suspend cache dmsetup reload cdata –table “0 65536 linear /dev/sdc 8192” dmsetup resume cdata dmsetup resume cache
KASAN reports:
BUG: KASAN: vmalloc-out-of-bounds in cache_preresume+0x269/0x7b0 Read of size 8 at addr ffffc900000f3080 by task dmsetup/131
(…snip…) The buggy address belongs to the virtual mapping at [ffffc900000f3000, ffffc900000f5000) created by: cache_ctr+0x176a/0x35f0
(…snip…) Memory state around the buggy address: ffffc900000f2f80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ffffc900000f3000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffffc900000f3080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ^ ffffc900000f3100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ffffc900000f3180: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
Fix by making the index post-incremented.