[PATCH 6.18.y 3/3] NFSD: stop registering with rpcbind after a failure in listener_set

[Sasha Levin <sashal@kernel.org>]

From: Jeff Layton <jlayton@kernel.org>

[ Upstream commit bf0f3a37e6ccb78ae80cc6eb2edde4f033c7574c ]

nfsd_nl_listener_set_doit() calls svc_xprt_create_from_sa() once for each
requested listener and passes flags of 0, so every listener registers with
rpcbind on its own. A rpcbind that accepts the connection and never replies
therefore costs one timeout for each entry. With the cap of 1024 entries
the request can hold nfsd_mutex for about 34 minutes, which is roughly 17
times the hung-task threshold.

One failure is enough to know that the next call will not fare better.
Read svc_rpcb_failure_count() before the create loop, and pass
SVC_SOCK_ANONYMOUS for the rest of the request once the count moves.

Fixes: 16a471177496 ("NFSD: add listener-{set,get} netlink command")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Link: https://syzkaller.appspot.com/bug?extid=c7eae0eb80858a2dba0f
Suggested-by: Olga Kornievskaia <okorniev@redhat.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260901-nfsd-nl-hang-v5-10-a540d86668b0@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/nfsd/nfsctl.c | 42 ++++++++++++++++++++++++++++++++++++++----
 1 file changed, 38 insertions(+), 4 deletions(-)

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 49cd0588deb39..9ffa72c15aed2 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -2029,7 +2029,10 @@ int nfsd_nl_listener_set_doit(struct sk_buff *skb, struct genl_info *info)
 	const struct nlattr *bad_attr = NULL;
 	struct svc_xprt *xprt, *tmp;
 	const char *bad_xprt = NULL;
+	unsigned int rpcb_failures;
 	const struct nlattr *attr;
+	bool skipped_rpcb = false;
+	bool bad_rpcb = false;
 	struct svc_serv *serv;
 	LIST_HEAD(permsocks);
 	struct nfsd_net *nn;
@@ -2119,13 +2122,16 @@ int nfsd_nl_listener_set_doit(struct sk_buff *skb, struct genl_info *info)
 	if (delete)
 		svc_xprt_destroy_all(serv, net, false);
 
+	rpcb_failures = svc_rpcb_failure_count(serv);
+
 	/* walk list of addrs again, open any that still don't exist */
 	nlmsg_for_each_attr_type(attr, NFSD_A_SERVER_SOCK_ADDR, info->nlhdr,
 				 GENL_HDRLEN, rem) {
 		struct nlattr *tb[NFSD_A_SOCK_MAX + 1];
 		const char *xcl_name;
 		struct sockaddr *sa;
-		int ret;
+		bool hit_rpcb;
+		int flags, ret;
 
 		/* validated up front in nfsd_nl_validate_listeners() */
 		if (nla_parse_nested(tb, NFSD_A_SOCK_MAX, attr,
@@ -2144,12 +2150,27 @@ int nfsd_nl_listener_set_doit(struct sk_buff *skb, struct genl_info *info)
 			continue;
 		}
 
-		ret = svc_xprt_create_from_sa(serv, xcl_name, net, sa, 0,
+		flags = skipped_rpcb ? SVC_SOCK_ANONYMOUS : 0;
+		ret = svc_xprt_create_from_sa(serv, xcl_name, net, sa, flags,
 					      current_cred());
+
+		hit_rpcb = false;
+		if (!skipped_rpcb &&
+		    svc_rpcb_failure_count(serv) != rpcb_failures) {
+			skipped_rpcb = true;
+			hit_rpcb = true;
+			if (ret < 0)
+				ret = svc_xprt_create_from_sa(serv, xcl_name,
+							      net, sa,
+							      SVC_SOCK_ANONYMOUS,
+							      current_cred());
+		}
+
 		/* always save the latest error */
 		if (ret < 0) {
 			bad_attr = attr;
 			bad_xprt = xcl_name;
+			bad_rpcb = hit_rpcb;
 			err = ret;
 		}
 	}
@@ -2161,8 +2182,21 @@ int nfsd_nl_listener_set_doit(struct sk_buff *skb, struct genl_info *info)
 	 */
 	if (err) {
 		NL_SET_BAD_ATTR(info->extack, bad_attr);
-		NL_SET_ERR_MSG_FMT(info->extack, "cannot create %s listener",
-				   bad_xprt);
+		if (bad_rpcb)
+			NL_SET_ERR_MSG_FMT(info->extack,
+					   "cannot create %s listener; rpcbind did not answer",
+					   bad_xprt);
+		else if (skipped_rpcb)
+			NL_SET_ERR_MSG_FMT(info->extack,
+					   "cannot create %s listener; rpcbind did not answer earlier, so some listeners are not registered",
+					   bad_xprt);
+		else
+			NL_SET_ERR_MSG_FMT(info->extack,
+					   "cannot create %s listener",
+					   bad_xprt);
+	} else if (skipped_rpcb) {
+		NL_SET_ERR_MSG(info->extack,
+			       "rpcbind did not answer, some listeners are not registered");
 	}
 
 	if (!serv->sv_nrthreads && list_empty(&nn->nfsd_serv->sv_permsocks))
-- 
2.53.0