CVE-2024-50278

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:

1. 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

2. 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

3. 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.

Weakness

The product reads data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
• To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/540.html

References

• https://git.kernel.org/stable/c/036dd6e3d2638103e0092864577ea1d091466b86
• https://git.kernel.org/stable/c/13ed3624c6ef283acefa4cc42cc8ae54fd4391a4
• https://git.kernel.org/stable/c/2222b0929d00e2d13732b799b63be391b5de4492
• https://git.kernel.org/stable/c/483b7261b35a9d369082ab298a6670912243f0be
• https://git.kernel.org/stable/c/c0ade5d98979585d4f5a93e4514c2e9a65afa08d
• https://git.kernel.org/stable/c/c52ec00cb2f9bebfada22edcc0db385b910a1cdb
• https://git.kernel.org/stable/c/e492f71854ce03474d49e87fd98b8df1f7cd1d2d
• https://git.kernel.org/stable/c/fdef3b94dfebd57e3077a578b6e309a2bb6fa688
• https://lists.debian.org/debian-lts-announce/2025/01/msg00001.html
• https://lists.debian.org/debian-lts-announce/2025/03/msg00002.html