CVE-2022-49551

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

usb: isp1760: Fix out-of-bounds array access

Running the driver through kasan gives an interesting splat:

BUG: KASAN: global-out-of-bounds in isp1760_register+0x180/0x70c Read of size 20 at addr f1db2e64 by task swapper/0/1 (…) isp1760_register from isp1760_plat_probe+0x1d8/0x220 (…)

This happens because the loop reading the regmap fields for the different ISP1760 variants look like this:

for (i = 0; i < HC_FIELD_MAX; i++) { … }

Meaning it expects the arrays to be at least HC_FIELD_MAX - 1 long.

However the arrays isp1760_hc_reg_fields[], isp1763_hc_reg_fields[], isp1763_hc_volatile_ranges[] and isp1763_dc_volatile_ranges[] are dynamically sized during compilation.

Fix this by putting an empty assignment to the [HC_FIELD_MAX] and [DC_FIELD_MAX] array member at the end of each array. This will make the array one member longer than it needs to be, but avoids the risk of overwriting whatever is inside [HC_FIELD_MAX - 1] and is simple and intuitive to read. Also add comments explaining what is going on.

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/26ae2c942b5702f2e43d36b2a4389cfb7d616b6a
• https://git.kernel.org/stable/c/463bddd3ff1acf4036ddb80c34a715eb99debf46
• https://git.kernel.org/stable/c/47d39cb57e8669e507d17d9e0d067d2b3e3a87ae
• https://git.kernel.org/stable/c/bf2558bbdce3ab1d6bcba09f354914e4515d0a2b