Subject: CVE-2024-50010: exec: don't WARN for racy path_noexec check

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

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

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

exec: don't WARN for racy path_noexec check

Both i_mode and noexec checks wrapped in WARN_ON stem from an artifact
of the previous implementation. They used to legitimately check for the
condition, but that got moved up in two commits:
633fb6ac3980 ("exec: move S_ISREG() check earlier")
0fd338b2d2cd ("exec: move path_noexec() check earlier")

Instead of being removed said checks are WARN_ON'ed instead, which
has some debug value.

However, the spurious path_noexec check is racy, resulting in
unwarranted warnings should someone race with setting the noexec flag.

One can note there is more to perm-checking whether execve is allowed
and none of the conditions are guaranteed to still hold after they were
tested for.

Additionally this does not validate whether the code path did any perm
checking to begin with -- it will pass if the inode happens to be
regular.

Keep the redundant path_noexec() check even though it's mindless
nonsense checking for guarantee that isn't given so drop the WARN.

Reword the commentary and do small tidy ups while here.

[brauner: keep redundant path_noexec() check]

The Linux kernel CVE team has assigned CVE-2024-50010 to this issue.

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

	Fixed in 6.11.3 with commit d62ba2a5536d
	Fixed in 6.12-rc1 with commit 0d196e7589ce

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-2024-50010
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:
	fs/exec.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/d62ba2a5536df83473a2ac15ab302258e3845251
	https://git.kernel.org/stable/c/0d196e7589cefe207d5d41f37a0a28a1fdeeb7c6