CVE-2022-50239

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

cpufreq: qcom: fix writes in read-only memory region

This commit fixes a kernel oops because of a write in some read-only memory:

[    9.068287] Unable to handle kernel write to read-only memory at virtual address ffff800009240ad8
..snip..
[    9.138790] Internal error: Oops: 9600004f [#1] PREEMPT SMP
..snip..
[    9.269161] Call trace:
[    9.276271]  __memcpy+0x5c/0x230
[    9.278531]  snprintf+0x58/0x80
[    9.282002]  qcom_cpufreq_msm8939_name_version+0xb4/0x190
[    9.284869]  qcom_cpufreq_probe+0xc8/0x39c
..snip..

The following line defines a pointer that point to a char buffer stored in read-only memory:

char *pvs_name = speedXX-pvsXX-vXX;

This pointer is meant to hold a template speedXX-pvsXX-vXX where the XX values get overridden by the qcom_cpufreq_krait_name_version function. Since the template is actually stored in read-only memory, when the function executes the following call we get an oops:

snprintf(*pvs_name, sizeof(speedXX-pvsXX-vXX), speed%d-pvs%d-v%d,
	 speed, pvs, pvs_ver);

To fix this issue, we instead store the template name onto the stack by using the following syntax:

char pvs_name_buffer[] = speedXX-pvsXX-vXX;

Because the pvs_name needs to be able to be assigned to NULL, the template buffer is stored in the pvs_name_buffer and not under the pvs_name variable.

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/01039fb8e90c9cb684430414bff70cea9eb168c5
• https://git.kernel.org/stable/c/14d260f94ff89543597ffea13db8b277a810e08e
• https://git.kernel.org/stable/c/794ded0bc461287a268bed21fea2eebb6e5d232c
• https://git.kernel.org/stable/c/b74ee4e301ca01e431e240c046173332966e2431