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.

Affected Products 3

References 8

• git.kernel.org https://git.kernel.org/stable/c/0643aa2468192a4d81326e8e76543854870b1ee2
• git.kernel.org https://git.kernel.org/stable/c/22191359f8454b0be082c3b126f86bcbea0f1318
• git.kernel.org https://git.kernel.org/stable/c/2fd0c26bacd90ef26522bd3169000a4715bf151f
  Patch
• git.kernel.org https://git.kernel.org/stable/c/591c788d16046edb0220800bf1819554af5853ce
• git.kernel.org https://git.kernel.org/stable/c/6279846b9b2532e1b04559ef8bd0dec049f29383
  Patch
• git.kernel.org https://git.kernel.org/stable/c/80a6b11862a7cfdf691e8f9faee89cfea219f098
  Patch
• git.kernel.org https://git.kernel.org/stable/c/c29dd8336236a4deb75596b52d2dd16ccc4a380d
• git.kernel.org https://git.kernel.org/stable/c/f01e06930444cab289a8783017af9b64255bd103
  Patch

Remediation

• git.kernel.org https://git.kernel.org/stable/c/2fd0c26bacd90ef26522bd3169000a4715bf151f
  Patch
• git.kernel.org https://git.kernel.org/stable/c/6279846b9b2532e1b04559ef8bd0dec049f29383
  Patch
• git.kernel.org https://git.kernel.org/stable/c/80a6b11862a7cfdf691e8f9faee89cfea219f098
  Patch
• git.kernel.org https://git.kernel.org/stable/c/f01e06930444cab289a8783017af9b64255bd103
  Patch