CVE-2024-44993

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

drm/v3d: Fix out-of-bounds read in v3d_csd_job_run()

When enabling UBSAN on Raspberry Pi 5, we get the following warning:

[ 387.894977] UBSAN: array-index-out-of-bounds in drivers/gpu/drm/v3d/v3d_sched.c:320:3 [ 387.903868] index 7 is out of range for type __u32 [7] [ 387.909692] CPU: 0 PID: 1207 Comm: kworker/u16:2 Tainted: G WC 6.10.3-v8-16k-numa #151 [ 387.919166] Hardware name: Raspberry Pi 5 Model B Rev 1.0 (DT) [ 387.925961] Workqueue: v3d_csd drm_sched_run_job_work [gpu_sched] [ 387.932525] Call trace: [ 387.935296] dump_backtrace+0x170/0x1b8 [ 387.939403] show_stack+0x20/0x38 [ 387.942907] dump_stack_lvl+0x90/0xd0 [ 387.946785] dump_stack+0x18/0x28 [ 387.950301] __ubsan_handle_out_of_bounds+0x98/0xd0 [ 387.955383] v3d_csd_job_run+0x3a8/0x438 [v3d] [ 387.960707] drm_sched_run_job_work+0x520/0x6d0 [gpu_sched] [ 387.966862] process_one_work+0x62c/0xb48 [ 387.971296] worker_thread+0x468/0x5b0 [ 387.975317] kthread+0x1c4/0x1e0 [ 387.978818] ret_from_fork+0x10/0x20 [ 387.983014] —[ end trace ]—

This happens because the UAPI provides only seven configuration registers and we are reading the eighth position of this u32 array.

Therefore, fix the out-of-bounds read in v3d_csd_job_run() by accessing only seven positions on the __u32 [7] array. The eighth register exists indeed on V3D 7.1, but it isnt currently used. That being so, lets guarantee that it remains unused and add a note that it could be set in a future patch.

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/497d370a644d95a9f04271aa92cb96d32e84c770
• https://git.kernel.org/stable/c/d656b82c4b30cf12715e6cd129d3df808fde24a7