Overview
About vulnerability
In the Linux kernel, the following vulnerability has been resolved:
dm cache: fix potential out-of-bounds access on the first resume
Out-of-bounds access occurs if the fast device is expanded unexpectedly before the first-time resume of the cache table. This happens because expanding the fast device requires reloading the cache table for cache_create to allocate new in-core data structures that fit the new size, and the check in cache_preresume is not performed during the first resume, leading to the issue.
Reproduce steps:
- prepare component devices:
dmsetup create cmeta –table “0 8192 linear /dev/sdc 0” dmsetup create cdata –table “0 65536 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
- load a cache table of 512 cache blocks, and deliberately expand the fast device before resuming the cache, making the in-core data structures inadequate.
dmsetup create cache –notable
dmsetup reload cache –table “0 524288 cache /dev/mapper/cmeta
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0”
dmsetup reload cdata –table “0 131072 linear /dev/sdc 8192”
dmsetup resume cdata
dmsetup resume cache
- suspend the cache to write out the in-core dirty bitset and hint array, leading to out-of-bounds access to the dirty bitset at offset 0x40:
dmsetup suspend cache
KASAN reports:
BUG: KASAN: vmalloc-out-of-bounds in is_dirty_callback+0x2b/0x80 Read of size 8 at addr ffffc90000085040 by task dmsetup/90
(…snip…) The buggy address belongs to the virtual mapping at [ffffc90000085000, ffffc90000087000) created by: cache_ctr+0x176a/0x35f0
(…snip…) Memory state around the buggy address: ffffc90000084f00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ffffc90000084f80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
ffffc90000085000: 00 00 00 00 00 00 00 00 f8 f8 f8 f8 f8 f8 f8 f8 ^ ffffc90000085080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ffffc90000085100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
Fix by checking the size change on the first resume.
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:
- kernel @ 4.18.0 (+8 more)
In the Linux kernel, the following vulnerability has been resolved:
dm cache: fix potential out-of-bounds access on the first resume
Out-of-bounds access occurs if the fast device is expanded unexpectedly before the first-time resume of the cache table. This happens because expanding the fast device requires reloading the cache table for cache_create to allocate new in-core data structures that fit the new size, and the check in cache_preresume is not performed during the first resume, leading to the issue.
Reproduce steps:
- prepare component devices:
dmsetup create cmeta –table “0 8192 linear /dev/sdc 0” dmsetup create cdata –table “0 65536 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
- load a cache table of 512 cache blocks, and deliberately expand the fast device before resuming the cache, making the in-core data structures inadequate.
dmsetup create cache –notable
dmsetup reload cache –table “0 524288 cache /dev/mapper/cmeta
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0”
dmsetup reload cdata –table “0 131072 linear /dev/sdc 8192”
dmsetup resume cdata
dmsetup resume cache
- suspend the cache to write out the in-core dirty bitset and hint array, leading to out-of-bounds access to the dirty bitset at offset 0x40:
dmsetup suspend cache
KASAN reports:
BUG: KASAN: vmalloc-out-of-bounds in is_dirty_callback+0x2b/0x80 Read of size 8 at addr ffffc90000085040 by task dmsetup/90
(…snip…) The buggy address belongs to the virtual mapping at [ffffc90000085000, ffffc90000087000) created by: cache_ctr+0x176a/0x35f0
(…snip…) Memory state around the buggy address: ffffc90000084f00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ffffc90000084f80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
ffffc90000085000: 00 00 00 00 00 00 00 00 f8 f8 f8 f8 f8 f8 f8 f8 ^ ffffc90000085080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ffffc90000085100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
Fix by checking the size change on the first resume.