CVE-2024-36016

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

tty: n_gsm: fix possible out-of-bounds in gsm0_receive()

Assuming the following:

• side A configures the n_gsm in basic option mode
• side B sends the header of a basic option mode frame with data length 1
• side A switches to advanced option mode
• side B sends 2 data bytes which exceeds gsm->len Reason: gsm->len is not used in advanced option mode.
• side A switches to basic option mode
• side B keeps sending until gsm0_receive() writes past gsm->buf Reason: Neither gsm->state nor gsm->len have been reset after reconfiguration.

Fix this by changing gsm->count to gsm->len comparison from equal to less than. Also add upper limit checks against the constant MAX_MRU in gsm0_receive() and gsm1_receive() to harden against memory corruption of gsm->len and gsm->mru.

All other checks remain as we still need to limit the data according to the user configuration and actual payload size.

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/0fb736c9931e02dbc7d9a75044c8e1c039e50f04
• https://git.kernel.org/stable/c/46f52c89a7e7d2691b97a9728e4591d071ca8abc
• https://git.kernel.org/stable/c/47388e807f85948eefc403a8a5fdc5b406a65d5a
• https://git.kernel.org/stable/c/4c267110fc110390704cc065edb9817fdd10ff54
• https://git.kernel.org/stable/c/774d83b008eccb1c48c14dc5486e7aa255731350
• https://git.kernel.org/stable/c/9513d4148950b05bc99fa7314dc883cc0e1605e5
• https://git.kernel.org/stable/c/b229bc6c6ea9fe459fc3fa94fd0a27a2f32aca56
• https://git.kernel.org/stable/c/b890d45aaf02b564e6cae2d2a590f9649330857d
• https://git.kernel.org/stable/c/f126ce7305fe88f49cdabc6db4168b9318898ea3