[PATCH v2 5/9] nfsd: widen nfsd_genl_rqstp address fields to sockaddr_storage

struct nfsd_genl_rqstp declares rq_daddr and rq_saddr as plain
"struct sockaddr" (16 bytes). When an IPv6 NFS client is connected,
nfsd_genl_rpc_status_compose_msg() casts these fields to
"struct sockaddr_in6 *" (28 bytes) and reads sin6_addr at offset 8..24,
which extends 8 bytes past the end of the 16-byte sockaddr field into
the adjacent rq_flags member. The 16-byte nla_put_in6_addr then ships 8
bytes of truncated IPv6 address followed by 8 bytes of rq_flags to
userspace via the NFSD_A_RPC_STATUS_SADDR6/DADDR6 netlink attributes.

This is reachable by any unprivileged process in the network namespace
because NFSD_CMD_RPC_STATUS_GET uses GENL_CMD_CAP_DUMP without
GENL_ADMIN_PERM.

Fix by widening rq_daddr and rq_saddr to struct sockaddr_storage so the
IPv6 casts operate within bounds, copying sizeof(struct sockaddr_storage)
bytes in the memcpy calls so the full address is captured, and
zero-initializing the genl_rqstp stack variable to prevent leaking
uninitialized tail bytes through netlink.

Fixes: bd9d6a3efa97 ("NFSD: add rpc_status netlink support")
Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Jeff Layton <[email protected]>
---
 fs/nfsd/nfsctl.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 92f65ca6f667..6fee49a7787f 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1414,8 +1414,8 @@ static int create_proc_exports_entry(void)
 unsigned int nfsd_net_id;
 
 struct nfsd_genl_rqstp {
-	struct sockaddr		rq_daddr;
-	struct sockaddr		rq_saddr;
+	struct sockaddr_storage	rq_daddr;
+	struct sockaddr_storage	rq_saddr;
 	unsigned long		rq_flags;
 	ktime_t			rq_stime;
 	__be32			rq_xid;
@@ -1450,7 +1450,7 @@ static int nfsd_genl_rpc_status_compose_msg(struct sk_buff *skb,
 			NFSD_A_RPC_STATUS_PAD))
 		return -ENOBUFS;
 
-	switch (genl_rqstp->rq_saddr.sa_family) {
+	switch (genl_rqstp->rq_saddr.ss_family) {
 	case AF_INET: {
 		const struct sockaddr_in *s_in, *d_in;
 
@@ -1527,7 +1527,7 @@ int nfsd_nl_rpc_status_get_dumpit(struct sk_buff *skb,
 		list_for_each_entry_rcu(rqstp,
 				&nn->nfsd_serv->sv_pools[i].sp_all_threads,
 				rq_all) {
-			struct nfsd_genl_rqstp genl_rqstp;
+			struct nfsd_genl_rqstp genl_rqstp = {};
 			unsigned int status_counter;
 
 			if (rqstp_index++ < cb->args[1]) /* already consumed */
@@ -1551,9 +1551,9 @@ int nfsd_nl_rpc_status_get_dumpit(struct sk_buff *skb,
 			genl_rqstp.rq_stime = rqstp->rq_stime;
 			genl_rqstp.rq_opcnt = 0;
 			memcpy(&genl_rqstp.rq_daddr, svc_daddr(rqstp),
-			       sizeof(struct sockaddr));
+			       sizeof(struct sockaddr_storage));
 			memcpy(&genl_rqstp.rq_saddr, svc_addr(rqstp),
-			       sizeof(struct sockaddr));
+			       sizeof(struct sockaddr_storage));
 
 #ifdef CONFIG_NFSD_V4
 			if (rqstp->rq_vers == NFS4_VERSION &&

-- 
2.54.0