netfilter: nf_tables: fix memleak when more than 255 elements expired

jira VUlN-597
cve CVE-2023-52581
commit-author Florian Westphal <[email protected]>
commit cf5000a
upstream-diff some cruft around GPL symbol exports

When more than 255 elements expired we're supposed to switch to a new gc
container structure.

This never happens: u8 type will wrap before reaching the boundary
and nft_trans_gc_space() always returns true.

This means we recycle the initial gc container structure and
lose track of the elements that came before.

While at it, don't deref 'gc' after we've passed it to call_rcu.

Fixes: 5f68718 ("netfilter: nf_tables: GC transaction API to avoid race with control plane")
	Reported-by: Pablo Neira Ayuso <[email protected]>
	Signed-off-by: Florian Westphal <[email protected]>
(cherry picked from commit cf5000a)
	Signed-off-by: Greg Rose <[email protected]>

include/net/netfilter/nf_tables.h

@@ -1494,7 +1494,7 @@ struct nft_trans_gc {
 	struct net		*net;
 	struct nft_set		*set;
 	u32			seq;
-	u8			count;
+	u16			count;
 	void			*priv[NFT_TRANS_GC_BATCHCOUNT];
 	struct rcu_head		rcu;
 };

net/netfilter/nf_tables_api.c

@@ -7955,12 +7955,15 @@ static int nft_trans_gc_space(struct nft_trans_gc *trans)
 struct nft_trans_gc *nft_trans_gc_queue_async(struct nft_trans_gc *gc,
 					      unsigned int gc_seq, gfp_t gfp)
 {
+	struct nft_set *set;
+
 	if (nft_trans_gc_space(gc))
 		return gc;
 
+	set = gc->set;
 	nft_trans_gc_queue_work(gc);
 
-	return nft_trans_gc_alloc(gc->set, gc_seq, gfp);
+	return nft_trans_gc_alloc(set, gc_seq, gfp);
 }
 EXPORT_SYMBOL_GPL(nft_trans_gc_queue_async);
 
@@ -7977,15 +7980,18 @@ EXPORT_SYMBOL_GPL(nft_trans_gc_queue_async_done);
 
 struct nft_trans_gc *nft_trans_gc_queue_sync(struct nft_trans_gc *gc, gfp_t gfp)
 {
+	struct nft_set *set;
+
 	if (WARN_ON_ONCE(!lockdep_commit_lock_is_held(gc->net)))
 		return NULL;
 
 	if (nft_trans_gc_space(gc))
 		return gc;
 
+	set = gc->set;
 	call_rcu(&gc->rcu, nft_trans_gc_trans_free);
 
-	return nft_trans_gc_alloc(gc->set, 0, gfp);
+	return nft_trans_gc_alloc(set, 0, gfp);
 }
 EXPORT_SYMBOL_GPL(nft_trans_gc_queue_sync);