Subject: CVE-2024-45020: bpf: Fix a kernel verifier crash in stacksafe()

From: Greg Kroah-Hartman <[email-masked]>

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

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

bpf: Fix a kernel verifier crash in stacksafe()

Daniel Hodges reported a kernel verifier crash when playing with sched-ext.
Further investigation shows that the crash is due to invalid memory access
in stacksafe(). More specifically, it is the following code:

    if (exact != NOT_EXACT &&
        old->stack[spi].slot_type[i % BPF_REG_SIZE] !=
        cur->stack[spi].slot_type[i % BPF_REG_SIZE])
            return false;

The 'i' iterates old->allocated_stack.
If cur->allocated_stack < old->allocated_stack the out-of-bound
access will happen.

To fix the issue add 'i >= cur->allocated_stack' check such that if
the condition is true, stacksafe() should fail. Otherwise,
cur->stack[spi].slot_type[i % BPF_REG_SIZE] memory access is legal.

The Linux kernel CVE team has assigned CVE-2024-45020 to this issue.

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

	Issue introduced in 6.6.15 with commit ab470fefce28 and fixed in 6.6.48 with commit 7cad3174cc79
	Issue introduced in 6.7 with commit 2793a8b015f7 and fixed in 6.10.7 with commit 6e3987ac310c
	Issue introduced in 6.7 with commit 2793a8b015f7 and fixed in 6.11 with commit bed2eb964c70

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-2024-45020
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/7cad3174cc79519bf5f6c4441780264416822c08
	https://git.kernel.org/stable/c/6e3987ac310c74bb4dd6a2fa8e46702fe505fb2b
	https://git.kernel.org/stable/c/bed2eb964c70b780fb55925892a74f26cb590b25