In the Linux kernel, the following vulnerability has been resolved: bpf: Mark NULL kptr stores precise check_map_kptr_access() permits a scalar store into an untrusted kptr field only when the register is known to contain zero

Overview

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

bpf: Mark NULL kptr stores precise

check_map_kptr_access() permits a scalar store into an untrusted kptr field only when the register is known to contain zero. Unlike other verifier checks whose outcome depends on a scalar value, it does not mark that register precise.

A state checkpoint reached with an imprecise zero can therefore prune a second path that reaches the store with an arbitrary nonzero scalar. The program can write attacker-controlled bits into the kptr field and load them back as a PTR_TO_BTF_ID.

Call mark_chain_precision() before accepting a known-zero register. This forces state equivalence to compare its scalar range and makes the verifier visit and reject a path carrying a nonzero value.

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

Vendor advisories

• Red Hat VEX · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · updated 2026-09-28 · vex