CVE-2025-39748

Description

In 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.

PUBLISHED Reserved 2025-04-16 | Published 2025-09-11 | Updated 2026-05-11 | Assigner Linux

Product status

References

git.kernel.org/...c/22191359f8454b0be082c3b126f86bcbea0f1318

git.kernel.org/...c/c29dd8336236a4deb75596b52d2dd16ccc4a380d

git.kernel.org/...c/591c788d16046edb0220800bf1819554af5853ce

git.kernel.org/...c/0643aa2468192a4d81326e8e76543854870b1ee2

git.kernel.org/...c/f01e06930444cab289a8783017af9b64255bd103

git.kernel.org/...c/2fd0c26bacd90ef26522bd3169000a4715bf151f

git.kernel.org/...c/80a6b11862a7cfdf691e8f9faee89cfea219f098

git.kernel.org/...c/6279846b9b2532e1b04559ef8bd0dec049f29383

cve.org (CVE-2025-39748)

nvd.nist.gov (CVE-2025-39748)

Download JSON