CVE-2026-98084

bpf: backtracking shouldn't clear outer frame R1-R5 for callbacks

State: Published
Severity: Not scored
Published: Sep 25, 2026
Updated: Oct 21, 2026
Reserved: Sep 25, 2026

Description

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

bpf: backtracking shouldn't clear outer frame R1-R5 for callbacks

When processing calls to bpf_loop() verifier marks R1 (and R4) as precise. R1 tracks loop iterations number and because of the 'callback_depth < R1' mechanics in check_helper_call() must be marked precise. However, precision propagation for R1 was broken, when bpf_loop() call was verified on a second iteration.

Consider the following verification trace: - main: bpf_loop(nr_loops, callback ...) - callback: BPF_EXIT - main: bpf_loop(nr_loops, callback ...) - ...

While the first visit of the call to bpf_loop() propagated R1 precision as expected, the second call to mark_chain_precision() in the check_helper_call() set R1, but it was immediately reset when backtrack_insn() processed preceding BPF_EXIT in the loop deleted in this patch.

Because of that, the second visit of the call to bpf_loop() injected checkpoint with R1 not marked as precise. Which could trick the verifier into accepting unsafe programs. See the next patch for an example of such program.

Commit is structured in a way to minimize conflicts when 'bpf' would be eventually merged with 'bpf-next'.

Scores

The record has no CVSS score.

Weaknesses

The record names no weakness.

Affected Products

Product	Versions
LinuxLinux	b43550d7d58e7ae6618aaab18c1e912fa4d6e3dd to before 1ac58dab0a83d2c64e3b807a3a0b399f17a74110Affected ab5cfac139ab8576fb54630d4cca23c3e690ee90 to before cdc93c6370f792d0649df2a145ac0cdcd430e411Affected ab5cfac139ab8576fb54630d4cca23c3e690ee90 to before 3a39bc9707fbd1bef4df7318a9d02222741dda5bAffected ab5cfac139ab8576fb54630d4cca23c3e690ee90 to before f83890dfed9efc5e19df1dbc1ad707a142936923Affected ab5cfac139ab8576fb54630d4cca23c3e690ee90 to before e3e4f66cc4b72333d0886ae2673c360248987889Affected 6.6.15 to before 6.6.160Affected
LinuxLinux	6.7Affected before 6.7Not affected 6.6.160 through 6.6.Not affected 6.12.114 through 6.12.Not affected 6.18.57 through 6.18.Not affected 7.2.7 through 7.2.Not affected 7.3 and laterNot affected

Product

Versions

LinuxLinux

b43550d7d58e7ae6618aaab18c1e912fa4d6e3dd to before 1ac58dab0a83d2c64e3b807a3a0b399f17a74110Affected
ab5cfac139ab8576fb54630d4cca23c3e690ee90 to before cdc93c6370f792d0649df2a145ac0cdcd430e411Affected
ab5cfac139ab8576fb54630d4cca23c3e690ee90 to before 3a39bc9707fbd1bef4df7318a9d02222741dda5bAffected
ab5cfac139ab8576fb54630d4cca23c3e690ee90 to before f83890dfed9efc5e19df1dbc1ad707a142936923Affected
ab5cfac139ab8576fb54630d4cca23c3e690ee90 to before e3e4f66cc4b72333d0886ae2673c360248987889Affected
6.6.15 to before 6.6.160Affected

LinuxLinux

6.7Affected
before 6.7Not affected
6.6.160 through 6.6.*Not affected
6.12.114 through 6.12.*Not affected
6.18.57 through 6.18.*Not affected
7.2.7 through 7.2.*Not affected
7.3 and laterNot affected

References

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