linux-cve-announce - CVE-2023-52928: bpf: Skip invalid kfunc call in backtrack

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Message-ID: <2025032718-CVE-2023-52928-e380@gregkh>
Date: Thu, 27 Mar 2025 17:37:18 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2023-52928: bpf: Skip invalid kfunc call in backtrack_insn

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

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

bpf: Skip invalid kfunc call in backtrack_insn

The verifier skips invalid kfunc call in check_kfunc_call(), which
would be captured in fixup_kfunc_call() if such insn is not eliminated
by dead code elimination. However, this can lead to the following
warning in backtrack_insn(), also see [1]:

  ------------[ cut here ]------------
  verifier backtracking bug
  WARNING: CPU: 6 PID: 8646 at kernel/bpf/verifier.c:2756 backtrack_insn
  kernel/bpf/verifier.c:2756
	__mark_chain_precision kernel/bpf/verifier.c:3065
	mark_chain_precision kernel/bpf/verifier.c:3165
	adjust_reg_min_max_vals kernel/bpf/verifier.c:10715
	check_alu_op kernel/bpf/verifier.c:10928
	do_check kernel/bpf/verifier.c:13821 [inline]
	do_check_common kernel/bpf/verifier.c:16289
  [...]

So make backtracking conservative with this by returning ENOTSUPP.

  [1] https://lore.kernel.org/bpf/CACkBjsaXNceR8ZjkLG=dT3P=4A8SBsg0Z5h5PWLryF5=ghKq=g@mail.gmail.com/

The Linux kernel CVE team has assigned CVE-2023-52928 to this issue.


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

	Fixed in 5.15.93 with commit 6e2fac197de2c4c041bdd8982cffb104689113f1
	Fixed in 6.1.11 with commit 74eec8266f37aff609db6a2f2b093e56a11c28c4
	Fixed in 6.2 with commit d3178e8a434b58678d99257c0387810a24042fb6

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-2023-52928
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/6e2fac197de2c4c041bdd8982cffb104689113f1
	https://git.kernel.org/stable/c/74eec8266f37aff609db6a2f2b093e56a11c28c4
	https://git.kernel.org/stable/c/d3178e8a434b58678d99257c0387810a24042fb6