netfilter: ctnetlink: allow userspace to modify labels

Add the ability to set/clear labels assigned to a conntrack
via ctnetlink.

To allow userspace to only alter specific bits, Pablo suggested to add
a new CTA_LABELS_MASK attribute:

The new set of active labels is then determined via

active = (active & ~mask) ^ changeset

i.e., the mask selects those bits in the existing set that should be
changed.

This follows the same method already used by MARK and CONNMARK targets.

Omitting CTA_LABELS_MASK is the same as setting all bits in CTA_LABELS_MASK
to 1: The existing set is replaced by the one from userspace.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 43 insertions, 0 deletions

diff --git a/net/netfilter/nf_conntrack_labels.c b/net/netfilter/nf_conntrack_labels.c
index ac5d0807d68137..e1d1eb850e7fce 100644
--- a/net/netfilter/nf_conntrack_labels.c
+++ b/net/netfilter/nf_conntrack_labels.c
@@ -52,6 +52,49 @@ int nf_connlabel_set(struct nf_conn *ct, u16 bit)
 }
 EXPORT_SYMBOL_GPL(nf_connlabel_set);
 
+#if IS_ENABLED(CONFIG_NF_CT_NETLINK)
+static void replace_u32(u32 *address, u32 mask, u32 new)
+{
+	u32 old, tmp;
+
+	do {
+		old = *address;
+		tmp = (old & mask) ^ new;
+	} while (cmpxchg(address, old, tmp) != old);
+}
+
+int nf_connlabels_replace(struct nf_conn *ct,
+			  const u32 *data,
+			  const u32 *mask, unsigned int words32)
+{
+	struct nf_conn_labels *labels;
+	unsigned int size, i;
+	u32 *dst;
+
+	labels = nf_ct_labels_find(ct);
+	if (!labels)
+		return -ENOSPC;
+
+	size = labels->words * sizeof(long);
+	if (size < (words32 * sizeof(u32)))
+		words32 = size / sizeof(u32);
+
+	dst = (u32 *) labels->bits;
+	if (words32) {
+		for (i = 0; i < words32; i++)
+			replace_u32(&dst[i], mask ? ~mask[i] : 0, data[i]);
+	}
+
+	size /= sizeof(u32);
+	for (i = words32; i < size; i++) /* pad */
+		replace_u32(&dst[i], 0, 0);
+
+	nf_conntrack_event_cache(IPCT_LABEL, ct);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(nf_connlabels_replace);
+#endif
+
 static struct nf_ct_ext_type labels_extend __read_mostly = {
 	.len    = sizeof(struct nf_conn_labels),
 	.align  = __alignof__(struct nf_conn_labels),