bpf: Forget ranges when refining tnum after JSET

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Summary

CVECVE-2025-39748
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2025-09-11 17:15:38 UTC
Updated2026-04-18 09:16:11 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: bpf: Forget ranges when refining tnum after JSET Syzbot reported a kernel warning due to a range invariant violation on the following BPF program. 0: call bpf_get_netns_cookie 1: if r0 == 0 goto <exit> 2: if r0 & Oxffffffff goto <exit> The issue is on the path where we fall through both jumps. That path is unreachable at runtime: after insn 1, we know r0 != 0, but with the sign extension on the jset, we would only fallthrough insn 2 if r0 == 0. Unfortunately, is_branch_taken() isn't currently able to figure this out, so the verifier walks all branches. The verifier then refines the register bounds using the second condition and we end up with inconsistent bounds on this unreachable path: 1: if r0 == 0 goto <exit> r0: u64=[0x1, 0xffffffffffffffff] var_off=(0, 0xffffffffffffffff) 2: if r0 & 0xffffffff goto <exit> r0 before reg_bounds_sync: u64=[0x1, 0xffffffffffffffff] var_off=(0, 0) r0 after reg_bounds_sync: u64=[0x1, 0] var_off=(0, 0) Improving the range refinement for JSET to cover all cases is tricky. We also don't expect many users to rely on JSET given LLVM doesn't generate those instructions. So instead of improving the range refinement for JSETs, Eduard suggested we forget the ranges whenever we're narrowing tnums after a JSET. This patch implements that approach.

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Problem Types: NVD-CWE-noinfo

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 960ea056561a08e2b837b2f02d22c53226414a84 22191359f8454b0be082c3b126f86bcbea0f1318 git Not specified
CNA Linux Linux affected 960ea056561a08e2b837b2f02d22c53226414a84 c29dd8336236a4deb75596b52d2dd16ccc4a380d git Not specified
CNA Linux Linux affected 960ea056561a08e2b837b2f02d22c53226414a84 591c788d16046edb0220800bf1819554af5853ce git Not specified
CNA Linux Linux affected 960ea056561a08e2b837b2f02d22c53226414a84 0643aa2468192a4d81326e8e76543854870b1ee2 git Not specified
CNA Linux Linux affected 960ea056561a08e2b837b2f02d22c53226414a84 f01e06930444cab289a8783017af9b64255bd103 git Not specified
CNA Linux Linux affected 960ea056561a08e2b837b2f02d22c53226414a84 2fd0c26bacd90ef26522bd3169000a4715bf151f git Not specified
CNA Linux Linux affected 960ea056561a08e2b837b2f02d22c53226414a84 80a6b11862a7cfdf691e8f9faee89cfea219f098 git Not specified
CNA Linux Linux affected 960ea056561a08e2b837b2f02d22c53226414a84 6279846b9b2532e1b04559ef8bd0dec049f29383 git Not specified
CNA Linux Linux affected 5.0 Not specified
CNA Linux Linux unaffected 5.0 semver Not specified
CNA Linux Linux unaffected 5.10.253 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.203 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.167 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.130 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.43 6.12.* semver Not specified
CNA Linux Linux unaffected 6.15.11 6.15.* semver Not specified
CNA Linux Linux unaffected 6.16.2 6.16.* semver Not specified
CNA Linux Linux unaffected 6.17 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/80a6b11862a7cfdf691e8f9faee89cfea219f098 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/2fd0c26bacd90ef26522bd3169000a4715bf151f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/22191359f8454b0be082c3b126f86bcbea0f1318 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/c29dd8336236a4deb75596b52d2dd16ccc4a380d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/591c788d16046edb0220800bf1819554af5853ce 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/f01e06930444cab289a8783017af9b64255bd103 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/0643aa2468192a4d81326e8e76543854870b1ee2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/6279846b9b2532e1b04559ef8bd0dec049f29383 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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