CVE-2023-52598

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

s390/ptrace: handle setting of fpc register correctly

If the content of the floating point control (fpc) register of a traced process is modified with the ptrace interface the new value is tested for validity by temporarily loading it into the fpc register.

This may lead to corruption of the fpc register of the tracing process: if an interrupt happens while the value is temporarily loaded into the fpc register, and within interrupt context floating point or vector registers are used, the current fp/vx registers are saved with save_fpu_regs() assuming they belong to user space and will be loaded into fp/vx registers when returning to user space.

test_fp_ctl() restores the original user space fpc register value, however it will be discarded, when returning to user space.

In result the tracer will incorrectly continue to run with the value that was supposed to be used for the traced process.

Fix this by saving fpu register contents with save_fpu_regs() before using test_fp_ctl().

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/02c6bbfb08bad78dd014e24c7b893723c15ec7a1
• https://git.kernel.org/stable/c/28a1f492cb527f64593457a0a0f0d809b3f36c25
• https://git.kernel.org/stable/c/6ccf904aac0292e1f6b1a1be6c407c414f7cf713
• https://git.kernel.org/stable/c/6d0822f2cc9b153bf2df49a84599195a2e0d21a8
• https://git.kernel.org/stable/c/7a4d6481fbdd661f9e40e95febb95e3dee82bad3
• https://git.kernel.org/stable/c/856caf2730ea18cb39e95833719c02a02447dc0a
• https://git.kernel.org/stable/c/8b13601d19c541158a6e18b278c00ba69ae37829
• https://git.kernel.org/stable/c/bdce67df7f12fb0409fbc604ce7c4254703f56d4
• https://git.kernel.org/stable/c/02c6bbfb08bad78dd014e24c7b893723c15ec7a1
• https://git.kernel.org/stable/c/28a1f492cb527f64593457a0a0f0d809b3f36c25
• https://git.kernel.org/stable/c/6ccf904aac0292e1f6b1a1be6c407c414f7cf713
• https://git.kernel.org/stable/c/6d0822f2cc9b153bf2df49a84599195a2e0d21a8
• https://git.kernel.org/stable/c/7a4d6481fbdd661f9e40e95febb95e3dee82bad3
• https://git.kernel.org/stable/c/856caf2730ea18cb39e95833719c02a02447dc0a
• https://git.kernel.org/stable/c/8b13601d19c541158a6e18b278c00ba69ae37829
• https://git.kernel.org/stable/c/bdce67df7f12fb0409fbc604ce7c4254703f56d4
• https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html