CVE-2022-49674

In the Linux kernel, the following vulnerability has been resolved:

dm raid: fix accesses beyond end of raid member array

On dm-raid table load (using raid_ctr), dm-raid allocates an array rs->devs[rs->raid_disks] for the raid device members. rs->raid_disks is defined by the number of raid metadata and image tupples passed into the targets constructor.

In the case of RAID layout changes being requested, that number can be different from the current number of members for existing raid sets as defined in their superblocks. Example RAID layout changes include:

• raid1 legs being added/removed
• raid4/5/6/10 number of stripes changed (stripe reshaping)
• takeover to higher raid level (e.g. raid5 -> raid6)

When accessing array members, rs->raid_disks must be used in control loops instead of the potentially larger value in rs->md.raid_disks. Otherwise it will cause memory access beyond the end of the rs->devs array.

Fix this by changing code that is prone to out-of-bounds access. Also fix validate_raid_redundancy() to validate all devices that are added. Also, use braces to help clean up raid_iterate_devices().

The out-of-bounds memory accesses was discovered using KASAN.

This commit was verified to pass all LVM2 RAID tests (with KASAN enabled).

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/332bd0778775d0cf105c4b9e03e460b590749916
• https://git.kernel.org/stable/c/5e161a8826b63c0b8b43e4a7fad1f956780f42ab
• https://git.kernel.org/stable/c/6352b2f4d8e95ec0ae576d7705435d64cfa29503
• https://git.kernel.org/stable/c/90de15357504c8097ab29769dc6852e16281e9e8
• https://git.kernel.org/stable/c/9bf2b0757b04c78dc5d6e3a198acca98457b32a1
• https://git.kernel.org/stable/c/bcff98500ea3b4e7615ec31d2bdd326bc1ef5134
• https://git.kernel.org/stable/c/df1a5ab0dd0775f2ea101c71f2addbc4c0ea0f85