Amazon Linux AMI: CVE-2024-50279: Security patch for kernel (ALAS-2025-1961)

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:

1. 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"

2. 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.