[PATCH 16/19] nfsd: validate sockaddr length per family in listener_set

[Jeff Layton]

nfsd_sock_nl_policy declares NFSD_A_SOCK_ADDR as bare NLA_BINARY
with no minimum length. A CAP_NET_ADMIN caller can send a 16-byte
NFSD_A_SOCK_ADDR with sa_family=AF_INET6, causing a 12-byte OOB
read across three consumers (rpc_cmp_addr_port, svc_find_listener,
kernel_bind).

Tighten the policy to NLA_POLICY_MIN_LEN(16) and add per-family
length validation in both nlmsg_for_each_attr_type loops.

Fixes: 16a471177496 ("NFSD: add listener-{set,get} netlink command")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
 Documentation/netlink/specs/nfsd.yaml |  4 ++++
 fs/nfsd/netlink.c                     |  2 +-
 fs/nfsd/nfsctl.c                      | 30 ++++++++++++++++++++++++++++++
 3 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/Documentation/netlink/specs/nfsd.yaml b/Documentation/netlink/specs/nfsd.yaml
index 8f36fadd68f7..9677ba19ffcd 100644
--- a/Documentation/netlink/specs/nfsd.yaml
+++ b/Documentation/netlink/specs/nfsd.yaml
@@ -156,6 +156,10 @@ attribute-sets:
       -
         name: addr
         type: binary
+        # 16 == sizeof(struct sockaddr_in); AF_INET6 callers
+        # validate the full sockaddr_in6 length in nfsctl.c.
+        checks:
+          min-len: 16
       -
         name: transport-name
         type: string
diff --git a/fs/nfsd/netlink.c b/fs/nfsd/netlink.c
index fbee3676d253..6570960034f1 100644
--- a/fs/nfsd/netlink.c
+++ b/fs/nfsd/netlink.c
@@ -37,7 +37,7 @@ const struct nla_policy nfsd_fslocations_nl_policy[NFSD_A_FSLOCATIONS_LOCATION +
 };
 
 const struct nla_policy nfsd_sock_nl_policy[NFSD_A_SOCK_TRANSPORT_NAME + 1] = {
-	[NFSD_A_SOCK_ADDR] = { .type = NLA_BINARY, },
+	[NFSD_A_SOCK_ADDR] = NLA_POLICY_MIN_LEN(16),
 	[NFSD_A_SOCK_TRANSPORT_NAME] = { .type = NLA_NUL_STRING, },
 };
 
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index ab10692ee937..f3b3154b16c5 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -2016,6 +2016,21 @@ int nfsd_nl_listener_set_doit(struct sk_buff *skb, struct genl_info *info)
 		xcl_name = nla_data(tb[NFSD_A_SOCK_TRANSPORT_NAME]);
 		sa = nla_data(tb[NFSD_A_SOCK_ADDR]);
 
+		switch (sa->sa_family) {
+		case AF_INET:
+			if (nla_len(tb[NFSD_A_SOCK_ADDR]) <
+			    sizeof(struct sockaddr_in))
+				continue;
+			break;
+		case AF_INET6:
+			if (nla_len(tb[NFSD_A_SOCK_ADDR]) <
+			    sizeof(struct sockaddr_in6))
+				continue;
+			break;
+		default:
+			continue;
+		}
+
 		/* Put back any matching sockets */
 		list_for_each_entry_safe(xprt, tmp, &permsocks, xpt_list) {
 			/* This shouldn't be possible */
@@ -2077,6 +2092,21 @@ int nfsd_nl_listener_set_doit(struct sk_buff *skb, struct genl_info *info)
 		xcl_name = nla_data(tb[NFSD_A_SOCK_TRANSPORT_NAME]);
 		sa = nla_data(tb[NFSD_A_SOCK_ADDR]);
 
+		switch (sa->sa_family) {
+		case AF_INET:
+			if (nla_len(tb[NFSD_A_SOCK_ADDR]) <
+			    sizeof(struct sockaddr_in))
+				continue;
+			break;
+		case AF_INET6:
+			if (nla_len(tb[NFSD_A_SOCK_ADDR]) <
+			    sizeof(struct sockaddr_in6))
+				continue;
+			break;
+		default:
+			continue;
+		}
+
 		xprt = svc_find_listener(serv, xcl_name, net, sa);
 		if (xprt) {
 			if (delete)

-- 
2.54.0