Description

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

bpf: Mark raw_tp arguments with PTR_MAYBE_NULL

Arguments to a raw tracepoint are tagged as trusted, which carries the
semantics that the pointer will be non-NULL. However, in certain cases,
a raw tracepoint argument may end up being NULL. More context about this
issue is available in [0].

Thus, there is a discrepancy between the reality, that raw_tp arguments
can actually be NULL, and the verifier's knowledge, that they are never
NULL, causing explicit NULL checks to be deleted, and accesses to such
pointers potentially crashing the kernel.

To fix this, mark raw_tp arguments as PTR_MAYBE_NULL, and then special
case the dereference and pointer arithmetic to permit it, and allow
passing them into helpers/kfuncs; these exceptions are made for raw_tp
programs only. Ensure that we don't do this when ref_obj_id > 0, as in
that case this is an acquired object and doesn't need such adjustment.

The reason we do mask_raw_tp_trusted_reg logic is because other will
recheck in places whether the register is a trusted_reg, and then
consider our register as untrusted when detecting the presence of the
PTR_MAYBE_NULL flag.

To allow safe dereference, we enable PROBE_MEM marking when we see loads
into trusted pointers with PTR_MAYBE_NULL.

While trusted raw_tp arguments can also be passed into helpers or kfuncs
where such broken assumption may cause issues, a future patch set will
tackle their case separately, as PTR...

Classification

CVE ID: CVE-2024-56702

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.04% (probability of being exploited)

EPSS Percentile: 5.08% (scored less or equal to compared to others)

EPSS Date: 2025-02-04 (when was this score calculated)

References

https://git.kernel.org/stable/c/c9b91d2d54175f781ad2c361cb2ac2c0e29b14b6
https://git.kernel.org/stable/c/3634d4a310820567fc634bf8f1ee2b91378773e8
https://git.kernel.org/stable/c/cb4158ce8ec8a5bb528cc1693356a5eb8058094d

Timeline