Overview
About vulnerability
In the Linux kernel, the following vulnerability has been resolved:
dm array: fix releasing a faulty array block twice in dm_array_cursor_end
When dm_bm_read_lock() fails due to locking or checksum errors, it releases the faulty block implicitly while leaving an invalid output pointer behind. The caller of dm_bm_read_lock() should not operate on this invalid dm_block pointer, or it will lead to undefined result. For example, the dm_array_cursor incorrectly caches the invalid pointer on reading a faulty array block, causing a double release in dm_array_cursor_end(), then hitting the BUG_ON in dm-bufio cache_put().
Reproduce steps:
- initialize a cache device
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 $262144”
dd if=/dev/zero of=/dev/mapper/cmeta bs=4k count=1
dmsetup create cache –table “0 524288 cache /dev/mapper/cmeta
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0”
- wipe the second array block offline
dmsteup remove cache cmeta cdata corig
mapping_root=$(dd if=/dev/sdc bs=1c count=8 skip=192
2>/dev/null | hexdump -e ‘1/8 “%u\n”’)
ablock=$(dd if=/dev/sdc bs=1c count=8 skip=$((4096*mapping_root+2056))
2>/dev/null | hexdump -e ‘1/8 “%u\n”’)
dd if=/dev/zero of=/dev/sdc bs=4k count=1 seek=$ablock
- try reopen the cache device
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”
dmsetup create cache –table “0 524288 cache /dev/mapper/cmeta
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0”
Kernel logs:
(snip) device-mapper: array: array_block_check failed: blocknr 0 != wanted 10 device-mapper: block manager: array validator check failed for block 10 device-mapper: array: get_ablock failed device-mapper: cache metadata: dm_array_cursor_next for mapping failed ————[ cut here ]———— kernel BUG at drivers/md/dm-bufio.c:638!
Fix by setting the cached block pointer to NULL on errors.
In addition to the reproducer described above, this fix can be verified using the “array_cursor/damaged” test in dm-unit: dm-unit run /pdata/array_cursor/damaged –kernel-dir <KERNEL_DIR>
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 (+7 more)
In the Linux kernel, the following vulnerability has been resolved:
dm array: fix releasing a faulty array block twice in dm_array_cursor_end
When dm_bm_read_lock() fails due to locking or checksum errors, it releases the faulty block implicitly while leaving an invalid output pointer behind. The caller of dm_bm_read_lock() should not operate on this invalid dm_block pointer, or it will lead to undefined result. For example, the dm_array_cursor incorrectly caches the invalid pointer on reading a faulty array block, causing a double release in dm_array_cursor_end(), then hitting the BUG_ON in dm-bufio cache_put().
Reproduce steps:
- initialize a cache device
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 $262144”
dd if=/dev/zero of=/dev/mapper/cmeta bs=4k count=1
dmsetup create cache –table “0 524288 cache /dev/mapper/cmeta
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0”
- wipe the second array block offline
dmsteup remove cache cmeta cdata corig
mapping_root=$(dd if=/dev/sdc bs=1c count=8 skip=192
2>/dev/null | hexdump -e ‘1/8 “%u\n”’)
ablock=$(dd if=/dev/sdc bs=1c count=8 skip=$((4096*mapping_root+2056))
2>/dev/null | hexdump -e ‘1/8 “%u\n”’)
dd if=/dev/zero of=/dev/sdc bs=4k count=1 seek=$ablock
- try reopen the cache device
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”
dmsetup create cache –table “0 524288 cache /dev/mapper/cmeta
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0”
Kernel logs:
(snip) device-mapper: array: array_block_check failed: blocknr 0 != wanted 10 device-mapper: block manager: array validator check failed for block 10 device-mapper: array: get_ablock failed device-mapper: cache metadata: dm_array_cursor_next for mapping failed ————[ cut here ]———— kernel BUG at drivers/md/dm-bufio.c:638!
Fix by setting the cached block pointer to NULL on errors.
In addition to the reproducer described above, this fix can be verified using the “array_cursor/damaged” test in dm-unit: dm-unit run /pdata/array_cursor/damaged –kernel-dir <KERNEL_DIR>