In the Linux kernel, the following vulnerability has been resolved:netfilter: nft_set_pipapo: do not free live elementPablo reports a crash with large batches of elements with aback-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 arule that maps to a non-deactivated element.Removal happens in two steps, first we do a lookup for key k and return theto-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 oneelement that share the same key.This can happen if we insert an element into a set when the set alreadyholds an element with same key, but the element mapping to the existingkey 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 becomesunreachable.The element that got deactivated (and will be freed later) willremain reachable in the set data structure, this can result ina crash when such an element is retrieved during lookup (stalepointer).Add a check that the fully matching key does in fact map to the elementthat 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 removefunction must not ever be called with an invisible/unreachable/non-existentelement.v2: avoid uneeded temporary variable (Stefano)
CWE-476 NULL Pointer Dereference