Subject: CVE-2024-26924: netfilter: nft_set_pipapo: do not free live element

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

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

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

netfilter: nft_set_pipapo: do not free live element

Pablo reports a crash with large batches of elements with a
back-to-back add/remove pattern.  Quoting Pablo:

  add_elem("00000000") timeout 100 ms
  ...
  add_elem("0000000X") timeout 100 ms
  del_elem("0000000X") <---------------- delete one that was just added
  ...
  add_elem("00005000") timeout 100 ms

  1) nft_pipapo_remove() removes element 0000000X
  Then, KASAN shows a splat.

Looking at the remove function there is a chance that we will drop a
rule that maps to a non-deactivated element.

Removal happens in two steps, first we do a lookup for key k and return the
to-be-removed element and mark it as inactive in the next generation.
Then, in a second step, the element gets removed from the set/map.

The _remove function does not work correctly if we have more than one
element that share the same key.

This can happen if we insert an element into a set when the set already
holds an element with same key, but the element mapping to the existing
key has timed out or is not active in the next generation.

In such case its possible that removal will unmap the wrong element.
If this happens, we will leak the non-deactivated element, it becomes
unreachable.

The element that got deactivated (and will be freed later) will
remain reachable in the set data structure, this can result in
a crash when such an element is retrieved during lookup (stale
pointer).

Add a check that the fully matching key does in fact map to the element
that we have marked as inactive in the deactivation step.
If not, we need to continue searching.

Add a bug/warn trap at the end of the function as well, the remove
function must not ever be called with an invisible/unreachable/non-existent
element.

v2: avoid uneeded temporary variable (Stefano)

The Linux kernel CVE team has assigned CVE-2024-26924 to this issue.

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

	Issue introduced in 5.6 with commit 3c4287f62044 and fixed in 5.10.216 with commit e3b887a9c11c
	Issue introduced in 5.6 with commit 3c4287f62044 and fixed in 5.15.157 with commit 7a1679e2d9bf
	Issue introduced in 5.6 with commit 3c4287f62044 and fixed in 6.1.88 with commit 41d8fdf3afaf
	Issue introduced in 5.6 with commit 3c4287f62044 and fixed in 6.6.29 with commit ebf7c9746f07
	Issue introduced in 5.6 with commit 3c4287f62044 and fixed in 6.8.8 with commit 14b001ba2211
	Issue introduced in 5.6 with commit 3c4287f62044 and fixed in 6.9 with commit 3cfc9ec039af

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-2024-26924
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/netfilter/nft_set_pipapo.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/e3b887a9c11caf8357a821260e095f2a694a34f2
	https://git.kernel.org/stable/c/7a1679e2d9bfa3b5f8755c2c7113e54b7d42bd46
	https://git.kernel.org/stable/c/41d8fdf3afaff312e17466e4ab732937738d5644
	https://git.kernel.org/stable/c/ebf7c9746f073035ee26209e38c3a1170f7b349a
	https://git.kernel.org/stable/c/14b001ba221136c15f894577253e8db535b99487
	https://git.kernel.org/stable/c/3cfc9ec039af60dbd8965ae085b2c2ccdcfbe1cc