CVE-2025-38004

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

can: bcm: add locking for bcm_op runtime updates

The CAN broadcast manager (CAN BCM) can send a sequence of CAN frames via hrtimer. The content and also the length of the sequence can be changed resp reduced at runtime where the currframe counter is then set to zero.

Although this appeared to be a safe operation the updates of currframe can be triggered from user space and hrtimer context in bcm_can_tx(). Anderson Nascimento created a proof of concept that triggered a KASAN slab-out-of-bounds read access which can be prevented with a spin_lock_bh.

At the rework of bcm_can_tx() the count variable has been moved into the protected section as this variable can be modified from both contexts too.

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/2a437b86ac5a9893c902f30ef66815bf13587bf6
• https://git.kernel.org/stable/c/7595de7bc56e0e52b74e56c90f7e247bf626d628
• https://git.kernel.org/stable/c/76c84c3728178b2d38d5604e399dfe8b0752645e
• https://git.kernel.org/stable/c/8f1c022541bf5a923c8d6fa483112c15250f30a4
• https://git.kernel.org/stable/c/c2aba69d0c36a496ab4f2e81e9c2b271f2693fd7
• https://git.kernel.org/stable/c/c4e8a172501e677ebd8ea9d9161d97dc4df56fbd
• https://git.kernel.org/stable/c/cc55dd28c20a6611e30596019b3b2f636819a4c0
• https://git.kernel.org/stable/c/fbd8fdc2b218e979cfe422b139b8f74c12419d1f
• https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html
• https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html