linux-cve-announce - CVE-2025-40143: bpf: dont report verifier bug for missing bpf_scc

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Message-ID: <2025111256-CVE-2025-40143-a4ce@gregkh>
Date: Wed, 12 Nov 2025 19:24:19 +0900
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40143: bpf: dont report verifier bug for missing bpf_scc_visit on speculative path

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

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

bpf: dont report verifier bug for missing bpf_scc_visit on speculative path

Syzbot generated a program that triggers a verifier_bug() call in
maybe_exit_scc(). maybe_exit_scc() assumes that, when called for a
state with insn_idx in some SCC, there should be an instance of struct
bpf_scc_visit allocated for that SCC. Turns out the assumption does
not hold for speculative execution paths. See example in the next
patch.

maybe_scc_exit() is called from update_branch_counts() for states that
reach branch count of zero, meaning that path exploration for a
particular path is finished. Path exploration can finish in one of
three ways:
a. Verification error is found. In this case, update_branch_counts()
   is called only for non-speculative paths.
b. Top level BPF_EXIT is reached. Such instructions are never a part of
   an SCC, so compute_scc_callchain() in maybe_scc_exit() will return
   false, and maybe_scc_exit() will return early.
c. A checkpoint is reached and matched. Checkpoints are created by
   is_state_visited(), which calls maybe_enter_scc(), which allocates
   bpf_scc_visit instances for checkpoints within SCCs.

Hence, for non-speculative symbolic execution paths, the assumption
still holds: if maybe_scc_exit() is called for a state within an SCC,
bpf_scc_visit instance must exist.

This patch removes the verifier_bug() call for speculative paths.

The Linux kernel CVE team has assigned CVE-2025-40143 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 6.17 with commit c9e31900b54cadf5398dfb838c0a63effa1defec and fixed in 6.17.3 with commit 3861e7c4324aa20a632fb74eb3904114f6afdb57
	Issue introduced in 6.17 with commit c9e31900b54cadf5398dfb838c0a63effa1defec and fixed in 6.18-rc1 with commit a3c73d629ea1373af3c0c954d41fd1af555492e3

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-40143
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	kernel/bpf/verifier.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/3861e7c4324aa20a632fb74eb3904114f6afdb57
	https://git.kernel.org/stable/c/a3c73d629ea1373af3c0c954d41fd1af555492e3