net: netfilter: Add kfuncs to set and change CT status

Introduce bpf_ct_set_status and bpf_ct_change_status kfunc helpers in
order to set nf_conn field of allocated entry or update nf_conn status
field of existing inserted entry. Use nf_ct_change_status_common to
share the permitted status field changes between netlink and BPF side
by refactoring ctnetlink_change_status.

It is required to introduce two kfuncs taking nf_conn___init and nf_conn
instead of sharing one because KF_TRUSTED_ARGS flag causes strict type
checking. This would disallow passing nf_conn___init to kfunc taking
nf_conn, and vice versa. We cannot remove the KF_TRUSTED_ARGS flag as we
only want to accept refcounted pointers and not e.g. ct->master.

Hence, bpf_ct_set_* kfuncs are meant to be used on allocated CT, and
bpf_ct_change_* kfuncs are meant to be used on inserted or looked up
CT entry.
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Co-developed-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20220721134245.2450-10-memxor@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

include/net/netfilter/nf_conntrack_core.h

@@ -98,6 +98,8 @@ static inline void __nf_ct_set_timeout(struct nf_conn *ct, u64 timeout)
 }
 
 int __nf_ct_change_timeout(struct nf_conn *ct, u64 cta_timeout);
+void __nf_ct_change_status(struct nf_conn *ct, unsigned long on, unsigned long off);
+int nf_ct_change_status_common(struct nf_conn *ct, unsigned int status);
 
 #endif
 

net/netfilter/nf_conntrack_bpf.c

@@ -394,6 +394,36 @@ int bpf_ct_change_timeout(struct nf_conn *nfct, u32 timeout)
 	return __nf_ct_change_timeout(nfct, msecs_to_jiffies(timeout));
 }
 
+/* bpf_ct_set_status - Set status field of allocated nf_conn
+ *
+ * Set the status field of the newly allocated nf_conn before insertion.
+ * This must be invoked for referenced PTR_TO_BTF_ID to nf_conn___init.
+ *
+ * Parameters:
+ * @nfct	 - Pointer to referenced nf_conn object, obtained using
+ *		   bpf_xdp_ct_alloc or bpf_skb_ct_alloc.
+ * @status       - New status value.
+ */
+int bpf_ct_set_status(const struct nf_conn___init *nfct, u32 status)
+{
+	return nf_ct_change_status_common((struct nf_conn *)nfct, status);
+}
+
+/* bpf_ct_change_status - Change status of inserted nf_conn
+ *
+ * Change the status field of the provided connection tracking entry.
+ * This must be invoked for referenced PTR_TO_BTF_ID to nf_conn.
+ *
+ * Parameters:
+ * @nfct	 - Pointer to referenced nf_conn object, obtained using
+ *		   bpf_ct_insert_entry, bpf_xdp_ct_lookup or bpf_skb_ct_lookup.
+ * @status       - New status value.
+ */
+int bpf_ct_change_status(struct nf_conn *nfct, u32 status)
+{
+	return nf_ct_change_status_common(nfct, status);
+}
+
 __diag_pop()
 
 BTF_SET8_START(nf_ct_kfunc_set)
@@ -405,6 +435,8 @@ BTF_ID_FLAGS(func, bpf_ct_insert_entry, KF_ACQUIRE | KF_RET_NULL | KF_RELEASE)
 BTF_ID_FLAGS(func, bpf_ct_release, KF_RELEASE)
 BTF_ID_FLAGS(func, bpf_ct_set_timeout, KF_TRUSTED_ARGS)
 BTF_ID_FLAGS(func, bpf_ct_change_timeout, KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, bpf_ct_set_status, KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, bpf_ct_change_status, KF_TRUSTED_ARGS)
 BTF_SET8_END(nf_ct_kfunc_set)
 
 static const struct btf_kfunc_id_set nf_conntrack_kfunc_set = {

net/netfilter/nf_conntrack_core.c

@@ -2807,4 +2807,44 @@ int __nf_ct_change_timeout(struct nf_conn *ct, u64 timeout)
 }
 EXPORT_SYMBOL_GPL(__nf_ct_change_timeout);
 
+void __nf_ct_change_status(struct nf_conn *ct, unsigned long on, unsigned long off)
+{
+	unsigned int bit;
+
+	/* Ignore these unchangable bits */
+	on &= ~IPS_UNCHANGEABLE_MASK;
+	off &= ~IPS_UNCHANGEABLE_MASK;
+
+	for (bit = 0; bit < __IPS_MAX_BIT; bit++) {
+		if (on & (1 << bit))
+			set_bit(bit, &ct->status);
+		else if (off & (1 << bit))
+			clear_bit(bit, &ct->status);
+	}
+}
+EXPORT_SYMBOL_GPL(__nf_ct_change_status);
+
+int nf_ct_change_status_common(struct nf_conn *ct, unsigned int status)
+{
+	unsigned long d;
+
+	d = ct->status ^ status;
+
+	if (d & (IPS_EXPECTED|IPS_CONFIRMED|IPS_DYING))
+		/* unchangeable */
+		return -EBUSY;
+
+	if (d & IPS_SEEN_REPLY && !(status & IPS_SEEN_REPLY))
+		/* SEEN_REPLY bit can only be set */
+		return -EBUSY;
+
+	if (d & IPS_ASSURED && !(status & IPS_ASSURED))
+		/* ASSURED bit can only be set */
+		return -EBUSY;
+
+	__nf_ct_change_status(ct, status, 0);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(nf_ct_change_status_common);
+
 #endif

net/netfilter/nf_conntrack_netlink.c

@@ -1890,45 +1890,10 @@ ctnetlink_parse_nat_setup(struct nf_conn *ct,
 }
 #endif
 
-static void
-__ctnetlink_change_status(struct nf_conn *ct, unsigned long on,
-			  unsigned long off)
-{
-	unsigned int bit;
-
-	/* Ignore these unchangable bits */
-	on &= ~IPS_UNCHANGEABLE_MASK;
-	off &= ~IPS_UNCHANGEABLE_MASK;
-
-	for (bit = 0; bit < __IPS_MAX_BIT; bit++) {
-		if (on & (1 << bit))
-			set_bit(bit, &ct->status);
-		else if (off & (1 << bit))
-			clear_bit(bit, &ct->status);
-	}
-}
-
 static int
 ctnetlink_change_status(struct nf_conn *ct, const struct nlattr * const cda[])
 {
-	unsigned long d;
-	unsigned int status = ntohl(nla_get_be32(cda[CTA_STATUS]));
-	d = ct->status ^ status;
-
-	if (d & (IPS_EXPECTED|IPS_CONFIRMED|IPS_DYING))
-		/* unchangeable */
-		return -EBUSY;
-
-	if (d & IPS_SEEN_REPLY && !(status & IPS_SEEN_REPLY))
-		/* SEEN_REPLY bit can only be set */
-		return -EBUSY;
-
-	if (d & IPS_ASSURED && !(status & IPS_ASSURED))
-		/* ASSURED bit can only be set */
-		return -EBUSY;
-
-	__ctnetlink_change_status(ct, status, 0);
-	return 0;
+	return nf_ct_change_status_common(ct, ntohl(nla_get_be32(cda[CTA_STATUS])));
 }
 
 static int
@@ -2825,7 +2790,7 @@ ctnetlink_update_status(struct nf_conn *ct, const struct nlattr * const cda[])
 	 * unchangeable bits but do not error out. Also user programs
 	 * are allowed to clear the bits that they are allowed to change.
 	 */
-	__ctnetlink_change_status(ct, status, ~status);
+	__nf_ct_change_status(ct, status, ~status);
 	return 0;
 }