CVE-2023-52928: bpf: Skip invalid kfunc call in backtrack_insn

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-03-27 · updated 2026-06-17

Description

In the Linux kernel, the following vulnerability has been resolved: bpf: Skip invalid kfunc call in backtrack_insn The verifier skips invalid kfunc call in check_kfunc_call(), which would be captured in fixup_kfunc_call() if such insn is not eliminated by dead code elimination. However, this can lead to the following warning in backtrack_insn(), also see [1]: ------------[ cut here ]------------ verifier backtracking bug WARNING: CPU: 6 PID: 8646 at kernel/bpf/verifier.c:2756 backtrack_insn kernel/bpf/verifier.c:2756 __mark_chain_precision kernel/bpf/verifier.c:3065 mark_chain_precision kernel/bpf/verifier.c:3165 adjust_reg_min_max_vals kernel/bpf/verifier.c:10715 check_alu_op kernel/bpf/verifier.c:10928 do_check kernel/bpf/verifier.c:13821 [inline] do_check_common kernel/bpf/verifier.c:16289 [...] So make backtracking conservative with this by returning ENOTSUPP. [1] https://lore.kernel.org/bpf/CACkBjsaXNceR8ZjkLG=dT3P=4A8SBsg0Z5h5PWLryF5=ghKq=g@mail.gmail.com/

Affected products

Linux kernel: from 5.13 before 5.15.93; from 5.16 before 6.1.11; 6.2-rc1, 6.2-rc2, 6.2-rc3, 6.2-rc4 — fixed in 5.15.93, 6.1.11

How to fix

Upgrade to a fixed version: Linux kernel 5.15.93, 6.1.11. Check the vendor advisory for mitigations.

References

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