Merge branch 'net-openvswitch-limit-the-recursions-from-action-sets'

Aaron Conole says:

====================
net: openvswitch: limit the recursions from action sets

Open vSwitch module accepts actions as a list from the netlink socket
and then creates a copy which it uses in the action set processing.
During processing of the action list on a packet, the module keeps a
count of the execution depth and exits processing if the action depth
goes too high.

However, during netlink processing the recursion depth isn't checked
anywhere, and the copy trusts that kernel has large enough stack to
accommodate it.  The OVS sample action was the original action which
could perform this kinds of recursion, and it originally checked that
it didn't exceed the sample depth limit.  However, when sample became
optimized to provide the clone() semantics, the recursion limit was
dropped.

This series adds a depth limit during the __ovs_nla_copy_actions() call
that will ensure we don't exceed the max that the OVS userspace could
generate for a clone().

Additionally, this series provides a selftest in 2/2 that can be used to
determine if the OVS module is allowing unbounded access.  It can be
safely omitted where the ovs selftest framework isn't available.
====================

Link: https://lore.kernel.org/r/20240207132416.1488485-1-aconole@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

3 files changed, 102 insertions, 31 deletions

diff --git a/net/openvswitch/flow_netlink.c b/net/openvswitch/flow_netlink.c
index 88965e2068ac..ebc5728aab4e 100644
--- a/net/openvswitch/flow_netlink.c
+++ b/net/openvswitch/flow_netlink.c
@@ -48,6 +48,7 @@ struct ovs_len_tbl {
 
 #define OVS_ATTR_NESTED -1
 #define OVS_ATTR_VARIABLE -2
+#define OVS_COPY_ACTIONS_MAX_DEPTH 16
 
 static bool actions_may_change_flow(const struct nlattr *actions)
 {
@@ -2545,13 +2546,15 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
 				  const struct sw_flow_key *key,
 				  struct sw_flow_actions **sfa,
 				  __be16 eth_type, __be16 vlan_tci,
-				  u32 mpls_label_count, bool log);
+				  u32 mpls_label_count, bool log,
+				  u32 depth);
 
 static int validate_and_copy_sample(struct net *net, const struct nlattr *attr,
 				    const struct sw_flow_key *key,
 				    struct sw_flow_actions **sfa,
 				    __be16 eth_type, __be16 vlan_tci,
-				    u32 mpls_label_count, bool log, bool last)
+				    u32 mpls_label_count, bool log, bool last,
+				    u32 depth)
 {
 	const struct nlattr *attrs[OVS_SAMPLE_ATTR_MAX + 1];
 	const struct nlattr *probability, *actions;
@@ -2602,7 +2605,8 @@ static int validate_and_copy_sample(struct net *net, const struct nlattr *attr,
 		return err;
 
 	err = __ovs_nla_copy_actions(net, actions, key, sfa,
-				     eth_type, vlan_tci, mpls_label_count, log);
+				     eth_type, vlan_tci, mpls_label_count, log,
+				     depth + 1);
 
 	if (err)
 		return err;
@@ -2617,7 +2621,8 @@ static int validate_and_copy_dec_ttl(struct net *net,
 				     const struct sw_flow_key *key,
 				     struct sw_flow_actions **sfa,
 				     __be16 eth_type, __be16 vlan_tci,
-				     u32 mpls_label_count, bool log)
+				     u32 mpls_label_count, bool log,
+				     u32 depth)
 {
 	const struct nlattr *attrs[OVS_DEC_TTL_ATTR_MAX + 1];
 	int start, action_start, err, rem;
@@ -2660,7 +2665,8 @@ static int validate_and_copy_dec_ttl(struct net *net,
 		return action_start;
 
 	err = __ovs_nla_copy_actions(net, actions, key, sfa, eth_type,
-				     vlan_tci, mpls_label_count, log);
+				     vlan_tci, mpls_label_count, log,
+				     depth + 1);
 	if (err)
 		return err;
 
@@ -2674,7 +2680,8 @@ static int validate_and_copy_clone(struct net *net,
 				   const struct sw_flow_key *key,
 				   struct sw_flow_actions **sfa,
 				   __be16 eth_type, __be16 vlan_tci,
-				   u32 mpls_label_count, bool log, bool last)
+				   u32 mpls_label_count, bool log, bool last,
+				   u32 depth)
 {
 	int start, err;
 	u32 exec;
@@ -2694,7 +2701,8 @@ static int validate_and_copy_clone(struct net *net,
 		return err;
 
 	err = __ovs_nla_copy_actions(net, attr, key, sfa,
-				     eth_type, vlan_tci, mpls_label_count, log);
+				     eth_type, vlan_tci, mpls_label_count, log,
+				     depth + 1);
 	if (err)
 		return err;
 
@@ -3063,7 +3071,7 @@ static int validate_and_copy_check_pkt_len(struct net *net,
 					   struct sw_flow_actions **sfa,
 					   __be16 eth_type, __be16 vlan_tci,
 					   u32 mpls_label_count,
-					   bool log, bool last)
+					   bool log, bool last, u32 depth)
 {
 	const struct nlattr *acts_if_greater, *acts_if_lesser_eq;
 	struct nlattr *a[OVS_CHECK_PKT_LEN_ATTR_MAX + 1];
@@ -3111,7 +3119,8 @@ static int validate_and_copy_check_pkt_len(struct net *net,
 		return nested_acts_start;
 
 	err = __ovs_nla_copy_actions(net, acts_if_lesser_eq, key, sfa,
-				     eth_type, vlan_tci, mpls_label_count, log);
+				     eth_type, vlan_tci, mpls_label_count, log,
+				     depth + 1);
 
 	if (err)
 		return err;
@@ -3124,7 +3133,8 @@ static int validate_and_copy_check_pkt_len(struct net *net,
 		return nested_acts_start;
 
 	err = __ovs_nla_copy_actions(net, acts_if_greater, key, sfa,
-				     eth_type, vlan_tci, mpls_label_count, log);
+				     eth_type, vlan_tci, mpls_label_count, log,
+				     depth + 1);
 
 	if (err)
 		return err;
@@ -3152,12 +3162,16 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
 				  const struct sw_flow_key *key,
 				  struct sw_flow_actions **sfa,
 				  __be16 eth_type, __be16 vlan_tci,
-				  u32 mpls_label_count, bool log)
+				  u32 mpls_label_count, bool log,
+				  u32 depth)
 {
 	u8 mac_proto = ovs_key_mac_proto(key);
 	const struct nlattr *a;
 	int rem, err;
 
+	if (depth > OVS_COPY_ACTIONS_MAX_DEPTH)
+		return -EOVERFLOW;
+
 	nla_for_each_nested(a, attr, rem) {
 		/* Expected argument lengths, (u32)-1 for variable length. */
 		static const u32 action_lens[OVS_ACTION_ATTR_MAX + 1] = {
@@ -3355,7 +3369,7 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
 			err = validate_and_copy_sample(net, a, key, sfa,
 						       eth_type, vlan_tci,
 						       mpls_label_count,
-						       log, last);
+						       log, last, depth);
 			if (err)
 				return err;
 			skip_copy = true;
@@ -3426,7 +3440,7 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
 			err = validate_and_copy_clone(net, a, key, sfa,
 						      eth_type, vlan_tci,
 						      mpls_label_count,
-						      log, last);
+						      log, last, depth);
 			if (err)
 				return err;
 			skip_copy = true;
@@ -3440,7 +3454,8 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
 							      eth_type,
 							      vlan_tci,
 							      mpls_label_count,
-							      log, last);
+							      log, last,
+							      depth);
 			if (err)
 				return err;
 			skip_copy = true;
@@ -3450,7 +3465,8 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
 		case OVS_ACTION_ATTR_DEC_TTL:
 			err = validate_and_copy_dec_ttl(net, a, key, sfa,
 							eth_type, vlan_tci,
-							mpls_label_count, log);
+							mpls_label_count, log,
+							depth);
 			if (err)
 				return err;
 			skip_copy = true;
@@ -3495,7 +3511,8 @@ int ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
 
 	(*sfa)->orig_len = nla_len(attr);
 	err = __ovs_nla_copy_actions(net, attr, key, sfa, key->eth.type,
-				     key->eth.vlan.tci, mpls_label_count, log);
+				     key->eth.vlan.tci, mpls_label_count, log,
+				     0);
 	if (err)
 		ovs_nla_free_flow_actions(*sfa);
 
diff --git a/tools/testing/selftests/net/openvswitch/openvswitch.sh b/tools/testing/selftests/net/openvswitch/openvswitch.sh
index f8499d4c87f3..36e40256ab92 100755
--- a/tools/testing/selftests/net/openvswitch/openvswitch.sh
+++ b/tools/testing/selftests/net/openvswitch/openvswitch.sh
@@ -502,9 +502,22 @@ test_netlink_checks () {
 	    wc -l) == 2 ] || \
 	      return 1
 
+	info "Checking clone depth"
 	ERR_MSG="Flow actions may not be safe on all matching packets"
 	PRE_TEST=$(dmesg | grep -c "${ERR_MSG}")
 	ovs_add_flow "test_netlink_checks" nv0 \
+		'in_port(1),eth(),eth_type(0x800),ipv4()' \
+		'clone(clone(clone(clone(clone(clone(clone(clone(clone(clone(clone(clone(clone(clone(clone(clone(clone(drop)))))))))))))))))' \
+		>/dev/null 2>&1 && return 1
+	POST_TEST=$(dmesg | grep -c "${ERR_MSG}")
+
+	if [ "$PRE_TEST" == "$POST_TEST" ]; then
+		info "failed - clone depth too large"
+		return 1
+	fi
+
+	PRE_TEST=$(dmesg | grep -c "${ERR_MSG}")
+	ovs_add_flow "test_netlink_checks" nv0 \
 		'in_port(1),eth(),eth_type(0x0806),arp()' 'drop(0),2' \
 		&> /dev/null && return 1
 	POST_TEST=$(dmesg | grep -c "${ERR_MSG}")
diff --git a/tools/testing/selftests/net/openvswitch/ovs-dpctl.py b/tools/testing/selftests/net/openvswitch/ovs-dpctl.py
index b97e621face9..5e0e539a323d 100644
--- a/tools/testing/selftests/net/openvswitch/ovs-dpctl.py
+++ b/tools/testing/selftests/net/openvswitch/ovs-dpctl.py
@@ -299,7 +299,7 @@ class ovsactions(nla):
         ("OVS_ACTION_ATTR_PUSH_NSH", "none"),
         ("OVS_ACTION_ATTR_POP_NSH", "flag"),
         ("OVS_ACTION_ATTR_METER", "none"),
-        ("OVS_ACTION_ATTR_CLONE", "none"),
+        ("OVS_ACTION_ATTR_CLONE", "recursive"),
         ("OVS_ACTION_ATTR_CHECK_PKT_LEN", "none"),
         ("OVS_ACTION_ATTR_ADD_MPLS", "none"),
         ("OVS_ACTION_ATTR_DEC_TTL", "none"),
@@ -465,29 +465,42 @@ class ovsactions(nla):
                     print_str += "pop_mpls"
             else:
                 datum = self.get_attr(field[0])
-                print_str += datum.dpstr(more)
+                if field[0] == "OVS_ACTION_ATTR_CLONE":
+                    print_str += "clone("
+                    print_str += datum.dpstr(more)
+                    print_str += ")"
+                else:
+                    print_str += datum.dpstr(more)
 
         return print_str
 
     def parse(self, actstr):
+        totallen = len(actstr)
         while len(actstr) != 0:
             parsed = False
+            parencount = 0
             if actstr.startswith("drop"):
                 # If no reason is provided, the implicit drop is used (i.e no
                 # action). If some reason is given, an explicit action is used.
-                actstr, reason = parse_extract_field(
-                    actstr,
-                    "drop(",
-                    "([0-9]+)",
-                    lambda x: int(x, 0),
-                    False,
-                    None,
-                )
+                reason = None
+                if actstr.startswith("drop("):
+                    parencount += 1
+
+                    actstr, reason = parse_extract_field(
+                        actstr,
+                        "drop(",
+                        "([0-9]+)",
+                        lambda x: int(x, 0),
+                        False,
+                        None,
+                    )
+
                 if reason is not None:
                     self["attrs"].append(["OVS_ACTION_ATTR_DROP", reason])
                     parsed = True
                 else:
-                    return
+                    actstr = actstr[len("drop"): ]
+                    return (totallen - len(actstr))
 
             elif parse_starts_block(actstr, "^(\d+)", False, True):
                 actstr, output = parse_extract_field(
@@ -504,6 +517,7 @@ class ovsactions(nla):
                     False,
                     0,
                 )
+                parencount += 1
                 self["attrs"].append(["OVS_ACTION_ATTR_RECIRC", recircid])
                 parsed = True
 
@@ -516,12 +530,22 @@ class ovsactions(nla):
 
             for flat_act in parse_flat_map:
                 if parse_starts_block(actstr, flat_act[0], False):
-                    actstr += len(flat_act[0])
+                    actstr = actstr[len(flat_act[0]):]
                     self["attrs"].append([flat_act[1]])
                     actstr = actstr[strspn(actstr, ", ") :]
                     parsed = True
 
-            if parse_starts_block(actstr, "ct(", False):
+            if parse_starts_block(actstr, "clone(", False):
+                parencount += 1
+                subacts = ovsactions()
+                actstr = actstr[len("clone("):]
+                parsedLen = subacts.parse(actstr)
+                lst = []
+                self["attrs"].append(("OVS_ACTION_ATTR_CLONE", subacts))
+                actstr = actstr[parsedLen:]
+                parsed = True
+            elif parse_starts_block(actstr, "ct(", False):
+                parencount += 1
                 actstr = actstr[len("ct(") :]
                 ctact = ovsactions.ctact()
 
@@ -553,6 +577,7 @@ class ovsactions(nla):
                         natact = ovsactions.ctact.natattr()
 
                         if actstr.startswith("("):
+                            parencount += 1
                             t = None
                             actstr = actstr[1:]
                             if actstr.startswith("src"):
@@ -607,15 +632,29 @@ class ovsactions(nla):
                                     actstr = actstr[strspn(actstr, ", ") :]
 
                         ctact["attrs"].append(["OVS_CT_ATTR_NAT", natact])
-                        actstr = actstr[strspn(actstr, ",) ") :]
+                        actstr = actstr[strspn(actstr, ", ") :]
 
                 self["attrs"].append(["OVS_ACTION_ATTR_CT", ctact])
                 parsed = True
 
-            actstr = actstr[strspn(actstr, "), ") :]
+            actstr = actstr[strspn(actstr, ", ") :]
+            while parencount > 0:
+                parencount -= 1
+                actstr = actstr[strspn(actstr, " "):]
+                if len(actstr) and actstr[0] != ")":
+                    raise ValueError("Action str: '%s' unbalanced" % actstr)
+                actstr = actstr[1:]
+
+            if len(actstr) and actstr[0] == ")":
+                return (totallen - len(actstr))
+
+            actstr = actstr[strspn(actstr, ", ") :]
+
             if not parsed:
                 raise ValueError("Action str: '%s' not supported" % actstr)
 
+        return (totallen - len(actstr))
+
 
 class ovskey(nla):
     nla_flags = NLA_F_NESTED
@@ -2111,6 +2150,8 @@ def main(argv):
     ovsflow = OvsFlow()
     ndb = NDB()
 
+    sys.setrecursionlimit(100000)
+
     if hasattr(args, "showdp"):
         found = False
         for iface in ndb.interfaces: