net: filter: fix possible memory leak in __sk_prepare_filter()

__sk_prepare_filter() was reworked in commit bd4cf0ed3 (net: filter:
rework/optimize internal BPF interpreter's instruction set) so that it should
have uncharged memory once things went wrong. However that work isn't complete.
Error is handled only in __sk_migrate_filter() while memory can still leak in
the error path right after sk_chk_filter().

Fixes: bd4cf0ed331a ("net: filter: rework/optimize internal BPF interpreter's instruction set")
Signed-off-by: Leon Yu <chianglungyu@gmail.com>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Tested-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/filter.c

@@ -1559,8 +1559,13 @@ static struct sk_filter *__sk_prepare_filter(struct sk_filter *fp,
 	fp->jited = 0;
 
 	err = sk_chk_filter(fp->insns, fp->len);
-	if (err)
+	if (err) {
+		if (sk != NULL)
+			sk_filter_uncharge(sk, fp);
+		else
+			kfree(fp);
 		return ERR_PTR(err);
+	}
 
 	/* Probe if we can JIT compile the filter and if so, do
 	 * the compilation of the filter.