netfilter: ctnetlink: fix mark based dump filtering regression

conntrack mark based dump filtering may falsely skip entries if a mask
is given: If the mask-based check does not filter out the entry, the
else-if check is always true and compares the mark without considering
the mask. The if/else-if logic seems wrong.

Given that the mask during filter setup is implicitly set to 0xffffffff
if not specified explicitly, the mark filtering flags seem to just
complicate things. Restore the previously used approach by always
matching against a zero mask is no filter mark is given.

Fixes: cb8aa9a3affb ("netfilter: ctnetlink: add kernel side filtering for dump")
Signed-off-by: Martin Willi <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

net/netfilter/nf_conntrack_netlink.c

···
 }
 
 struct ctnetlink_filter {
-	u_int32_t cta_flags;
 	u8 family;
 
 	u_int32_t orig_flags;
···
 					 struct nf_conntrack_zone *zone,
 					 u_int32_t flags);
 
-/* applied on filters */
-#define CTA_FILTER_F_CTA_MARK			(1 << 0)
-#define CTA_FILTER_F_CTA_MARK_MASK		(1 << 1)
-
 static struct ctnetlink_filter *
 ctnetlink_alloc_filter(const struct nlattr * const cda[], u8 family)
 {
···
 #ifdef CONFIG_NF_CONNTRACK_MARK
 	if (cda[CTA_MARK]) {
 		filter->mark.val = ntohl(nla_get_be32(cda[CTA_MARK]));
-		filter->cta_flags |= CTA_FILTER_FLAG(CTA_MARK);
-
-		if (cda[CTA_MARK_MASK]) {
+		if (cda[CTA_MARK_MASK])
 			filter->mark.mask = ntohl(nla_get_be32(cda[CTA_MARK_MASK]));
-			filter->cta_flags |= CTA_FILTER_FLAG(CTA_MARK_MASK);
-		} else {
+		else
 			filter->mark.mask = 0xffffffff;
-		}
 	} else if (cda[CTA_MARK_MASK]) {
 		err = -EINVAL;
 		goto err_filter;
···
 	}
 
 #ifdef CONFIG_NF_CONNTRACK_MARK
-	if ((filter->cta_flags & CTA_FILTER_FLAG(CTA_MARK_MASK)) &&
-	    (ct->mark & filter->mark.mask) != filter->mark.val)
-		goto ignore_entry;
-	else if ((filter->cta_flags & CTA_FILTER_FLAG(CTA_MARK)) &&
-		 ct->mark != filter->mark.val)
+	if ((ct->mark & filter->mark.mask) != filter->mark.val)
 		goto ignore_entry;
 #endif