netfilter: nft_set_pipapo: fix improper element removal

jira LE-1907
cve CVE-2023-4004
Rebuild_History Non-Buildable kernel-5.14.0-284.30.1.el9_2
commit-author Florian Westphal <[email protected]>
commit 87b5a5c

end key should be equal to start unless NFT_SET_EXT_KEY_END is present.

Its possible to add elements that only have a start key
("{ 1.0.0.0 . 2.0.0.0 }") without an internval end.

Insertion treats this via:

if (nft_set_ext_exists(ext, NFT_SET_EXT_KEY_END))
   end = (const u8 *)nft_set_ext_key_end(ext)->data;
else
   end = start;

but removal side always uses nft_set_ext_key_end().
This is wrong and leads to garbage remaining in the set after removal
next lookup/insert attempt will give:

BUG: KASAN: slab-use-after-free in pipapo_get+0x8eb/0xb90
Read of size 1 at addr ffff888100d50586 by task nft-pipapo_uaf_/1399
Call Trace:
 kasan_report+0x105/0x140
 pipapo_get+0x8eb/0xb90
 nft_pipapo_insert+0x1dc/0x1710
 nf_tables_newsetelem+0x31f5/0x4e00
 ..

Fixes: 3c4287f ("nf_tables: Add set type for arbitrary concatenation of ranges")
	Reported-by: lonial con <[email protected]>
	Reviewed-by: Stefano Brivio <[email protected]>
	Signed-off-by: Florian Westphal <[email protected]>
(cherry picked from commit 87b5a5c)
	Signed-off-by: Jonathan Maple <[email protected]>

Author: PlaidCat

net/netfilter/nft_set_pipapo.c

@@ -1908,7 +1908,11 @@ static void nft_pipapo_remove(const struct net *net, const struct nft_set *set,
 		int i, start, rules_fx;
 
 		match_start = data;
-		match_end = (const u8 *)nft_set_ext_key_end(&e->ext)->data;
+
+		if (nft_set_ext_exists(&e->ext, NFT_SET_EXT_KEY_END))
+			match_end = (const u8 *)nft_set_ext_key_end(&e->ext)->data;
+		else
+			match_end = data;
 
 		start = first_rule;
 		rules_fx = rules_f0;