CVE-2025-39685

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

comedi: pcl726: Prevent invalid irq number

The reproducer passed in an irq number(0x80008000) that was too large, which triggered the oob.

Added an interrupt number check to prevent users from passing in an irq number that was too large.

If it->options[1] is 31, then 1 << it->options[1] is still invalid because it shifts a 1-bit into the sign bit (which is UB in C). Possible solutions include reducing the upper bound on the it->options[1] value to 30 or lower, or using 1U << it->options[1].

The old code would just not attempt to request the IRQ if the options[1] value were invalid. And it would still configure the device without interrupts even if the call to request_irq returned an error. So it would be better to combine this test with the test below.

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/0eb4ed2aa261dee228f1668dbfa6d87353e8162d
• https://git.kernel.org/stable/c/5a33d07c94ba91306093e823112a7aa9727549f6
• https://git.kernel.org/stable/c/96cb948408b3adb69df7e451ba7da9d21f814d00
• https://git.kernel.org/stable/c/a3cfcd0c78c80ca7cd80372dc28f77d01be57bf6
• https://git.kernel.org/stable/c/bab220b0bb5af652007e278e8e8357f952b0e1ea
• https://git.kernel.org/stable/c/d8992c9a01f81128f36acb7c5755530e21fcd059
• https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html