CVE-2024-26924

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)

Notes