CVE-2026-74689: net/atm: fix slab-out-of-bounds read in vcc_setsockopt()

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

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

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

net/atm: fix slab-out-of-bounds read in vcc_setsockopt()

vcc_setsockopt() contained an ineffective optlen check:
  if (__SO_LEVEL_MATCH(optname, level) && optlen != __SO_SIZE(optname))
      return -EINVAL;

If __SO_LEVEL_MATCH(optname, level) evaluated to false (e.g. if the caller
passed a mismatched level), the length check optlen != __SO_SIZE(optname)
was short-circuited and bypassed. Execution then fell through to switch(optname),
calling copy_from_sockptr() assuming optval contained sufficient space.

Furthermore, even if level matched, a cgroup BPF setsockopt filter could shrink
optlen after entry. Because copy_from_sockptr() on kernel pointers uses memcpy(),
this leads to a KASAN slab-out-of-bounds read when optlen is smaller than the
expected structure size.

Fix this by using copy_safe_from_sockptr(), which unconditionally validates
that optlen is at least the expected size before copying. Also change the local
'value' variable type from 'unsigned long' to 'int' so that SO_SETCLP matches
its sizeof(int) ABI encoding on 64-bit systems.

The Linux kernel CVE team has assigned CVE-2026-74689 to this issue.


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

	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.1.183 with commit b3bcd5d65ac03c15787b2a5b36c718e26a689336
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.6.152 with commit 35f258fee9ed358c6d0f57f91c30bf029c3724af
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.12.104 with commit 6eb6af88710977eb529b558a07294874d8c40c4d
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.18.45 with commit 9f77c1ab382188f5b51982fab6d913443b6dc59f
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.1.9 with commit 2c5988c7349c0b64a7e0441bfc6e1dca54f7116a
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.2 with commit d0c80dbb970439bd2eeb0e5effff8c16a5f4e1e3

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-2026-74689
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:
	net/atm/common.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/b3bcd5d65ac03c15787b2a5b36c718e26a689336
	https://git.kernel.org/stable/c/35f258fee9ed358c6d0f57f91c30bf029c3724af
	https://git.kernel.org/stable/c/6eb6af88710977eb529b558a07294874d8c40c4d
	https://git.kernel.org/stable/c/9f77c1ab382188f5b51982fab6d913443b6dc59f
	https://git.kernel.org/stable/c/2c5988c7349c0b64a7e0441bfc6e1dca54f7116a
	https://git.kernel.org/stable/c/d0c80dbb970439bd2eeb0e5effff8c16a5f4e1e3