[PATCH v2 0/8] nfsd/sunrpc: harden the netlink listener interfaces

[PATCH v2 0/8] nfsd/sunrpc: harden the netlink listener interfaces

[Jeff Layton]

This version fixes a number of problems that Sashiko pointed out. The
more serious ones were preexisting issues, but we might as well fix
them while we're in the area. As before, the real way to address the
issues that syzbot keeps reporting is to make the rpcbind calls run
asynchronously.

syzbot keeps landing in nfsd_nl_listener_set_doit(), where a stall under
nfsd_mutex blocks every other NFSD netlink op. This is hardening rather than
a fix for any one report: it narrows what userland can push into that path
and shortens the worst stalls.

  1: reject transport names NFSD cannot instantiate, before nfsd_mutex is
     taken
  2: cap a listener_set request at 1024 entries
  3: stop svc_register() losing a registration error to a later program
  4: undo the registrations svc_register() made before it failed
  5: bound the local rpcbind client to a single 1s attempt
  6: report listener creation failures through extack
  7: listener_set validation tests
  8: a per-netns rpcbind stub, and the listener round-trip tests

Measured against a local rpcbind that accepts the connection and never
replies. The wait is paid per listener, since svc_xprt_create_from_sa()
passes flags of 0 and every listener therefore calls svc_register():

  per rpcbind call   10s AF_LOCAL, 60s loopback TCP  ->  1s
  per listener       20s / 120s                      ->  2s
  entries/request    bounded only by message size    ->  1024
  worst request      unbounded                       ->  ~34min

Three things this does not do:

- "rdma" is still accepted, so 1024 entries can still mean 1024
  request_module("svcrdma") upcalls under nfsd_mutex where svcrdma is
  unavailable. Not counted above.
- write_ports() reaches the same code with the same mutex held. It is
  legacy, so it is left alone.
- ~34min is still ~17x the hung-task threshold, so the reproducer should be
  expected to keep tripping the watchdog. The durable fix is to make rpcbind
  registration asynchronous so those RPCs stop running under nfsd_mutex at
  all. That needs behavioural changes we should discuss first, so it is a
  separate patchset.

Patch 3 is a flag day for CONFIG_NFS_LOCALIO=y: a registration failure now
aborts listener creation there too, matching CONFIG_NFS_LOCALIO=n. Details
in that patch.

Please consider these for v7.4.

To: Chuck Lever <cel@kernel.org>
To: NeilBrown <neil@brown.name>
To: Olga Kornievskaia <okorniev@redhat.com>
To: Dai Ngo <Dai.Ngo@oracle.com>
To: Tom Talpey <tom@talpey.com>
To: Trond Myklebust <trondmy@kernel.org>
To: Anna Schumaker <anna@kernel.org>
To: David S. Miller <davem@davemloft.net>
To: Eric Dumazet <edumazet@google.com>
To: Jakub Kicinski <kuba@kernel.org>
To: Paolo Abeni <pabeni@redhat.com>
To: Simon Horman <horms@kernel.org>
To: J. Bruce Fields <bfields@fieldses.org>
To: Shuah Khan <shuah@kernel.org>
Cc: linux-nfs@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: Trond Myklebust <trondmy@gmail.com>
Cc: linux-kselftest@vger.kernel.org
Signed-off-by: Jeff Layton <jlayton@kernel.org>

--- Changes in v2:
- New patch 4: svc_register() left the entries it had already set in
  rpcbind when a later one failed, pointing at a port the caller then
  closed.
- Tests: Behavioral fixes for several tests: several assertions only
  checked an errno that both the fixed and the broken kernel return.
  val_bad_transport() now requires that the rpcbind stub saw no traffic,
  val_second_entry_bad() that no listener came up, func_empty_destroys
  that the local rpcbind client was dropped and had to reconnect, and the
  two -EBUSY tests that the listener set is unchanged. find_listener()
  matches the address too.
- Tests: the stub read the revents of a freshly accepted pollfd that
  poll() had not written, so it could enter a blocking read with no
  readiness event.
- Tests: the config fragment gained NAMESPACES, SHMEM, TMPFS and UNIX;
  without them every test skipped.
- Link to v1: https://lore.kernel.org/r/20260810-nfsd-nl-hang-v1-0-2519fdd5bc1a@kernel.org

---
Jeff Layton (8):
      NFSD: validate transport name in listener_set before serv creation
      NFSD: cap the number of listeners accepted in listener_set
      SUNRPC: keep the first error in svc_register()
      SUNRPC: undo partial rpcbind registrations when svc_register() fails
      SUNRPC: bound the local rpcbind client timeout to 1s
      NFSD: report listener creation failures through extack
      selftests/nfsd: exercise listener_set request validation
      selftests/nfsd: add a per-netns rpcbind stub and the listener round-trips

 fs/nfsd/nfsctl.c                                   |   42 +-
 net/sunrpc/rpcb_clnt.c                             |   12 +
 net/sunrpc/svc.c                                   |   40 +-
 tools/testing/selftests/Makefile                   |    1 +
 tools/testing/selftests/nfsd/.gitignore            |    1 +
 tools/testing/selftests/nfsd/Makefile              |    6 +
 tools/testing/selftests/nfsd/config                |    8 +
 .../testing/selftests/nfsd/nfsd_netlink_listener.c | 1030 ++++++++++++++++++++
 tools/testing/selftests/nfsd/settings              |    1 +
 9 files changed, 1131 insertions(+), 10 deletions(-)
---
base-commit: 0b6d2c7e3abca8d17fddeecb6e4c32a8438ec2fb
change-id: 20260717-nfsd-nl-hang-10a3b3e93f2a

Best regards,
-- 
Jeff Layton <jlayton@kernel.org>

[PATCH v2 1/8] NFSD: validate transport name in listener_set before serv creation

[Jeff Layton]

nfsd_nl_listener_set_doit() holds nfsd_mutex across the whole listener
teardown/rebuild. NFSD_A_SOCK_TRANSPORT_NAME is only checked for
presence, not content, so an arbitrary name reaches
svc_xprt_create_from_sa(), where a name matching no registered class
triggers request_module("svc%s", name) -- a TASK_KILLABLE usermode-helper
upcall run under nfsd_mutex.

Vet the name against the classes NFSD can instantiate (tcp, udp, rdma) in
nfsd_nl_validate_listeners(), which runs before nfsd_mutex is taken.

This narrows the upcall rather than removing it. "rdma" is accepted
unconditionally, so on a kernel where svcrdma is not built it still
reaches request_module("svcrdma") under nfsd_mutex -- as it must for the
modular case, where autoloading is legitimate.

Assisted-by: LLM
Link: https://syzkaller.appspot.com/bug?extid=c7eae0eb80858a2dba0f
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/nfsd/nfsctl.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 4e5e083d8477..e5844d8454b8 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1975,14 +1975,31 @@ int nfsd_nl_version_get_doit(struct sk_buff *skb, struct genl_info *info)
 	return err;
 }
 
+/*
+ * Transport classes NFSD knows how to instantiate. Vetting the name here
+ * keeps a bogus string from reaching svc_xprt_create_from_sa(), where an
+ * unknown name triggers a request_module("svc%s", name) upcall under
+ * nfsd_mutex.
+ */
+static bool nfsd_nl_transport_supported(const char *name)
+{
+	static const char * const supported[] = { "tcp", "udp", "rdma" };
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(supported); i++)
+		if (!strcmp(name, supported[i]))
+			return true;
+	return false;
+}
+
 /**
  * nfsd_nl_validate_listeners - sanity-check the listener list from userland
  * @info: netlink metadata and command arguments
  *
  * Walk every NFSD_A_SERVER_SOCK_ADDR attribute and confirm that each entry
  * is well-formed: it parses against the policy, carries both an address and
- * a transport name, and the address is long enough for its family. Doing
- * this up front lets the callers below assume every entry is valid and
+ * a supported transport name, and the address is long enough for its family.
+ * Doing this up front lets the callers below assume every entry is valid and
  * guarantees we make no changes when the request is malformed.
  *
  * Return: 0 if every entry is valid, or a negative errno otherwise.
@@ -2006,6 +2023,9 @@ static int nfsd_nl_validate_listeners(struct genl_info *info)
 		if (!tb[NFSD_A_SOCK_ADDR] || !tb[NFSD_A_SOCK_TRANSPORT_NAME])
 			return -EINVAL;
 
+		if (!nfsd_nl_transport_supported(nla_data(tb[NFSD_A_SOCK_TRANSPORT_NAME])))
+			return -EPROTONOSUPPORT;
+
 		sa = nla_data(tb[NFSD_A_SOCK_ADDR]);
 		if (nla_len(tb[NFSD_A_SOCK_ADDR]) < sizeof(sa->sa_family))
 			return -EINVAL;

-- 
2.55.0

[PATCH v2 2/8] NFSD: cap the number of listeners accepted in listener_set

[Jeff Layton]

nfsd_nl_listener_set_doit() matches each requested listener against the
existing set in a nested loop that is O(N * M) in the requested (N) and
existing (M) counts, run under sv_lock with bottom halves disabled. A
userland request with a very large listener list can therefore spin in
atomic context for a long time.

Reject requests carrying more than NFSD_NL_LISTENER_MAX (1024) entries in
nfsd_nl_validate_listeners(), before any lock is taken. The limit is far
above any realistic configuration.

M is not capped here: write_ports() can add listeners too, via
svc_addsock() and svc_xprt_create(). But each one costs a real socket, so M
is bounded by resources, where N was bounded only by the message size.
Capping N leaves ~1M iterations plus 1024 nla_parse_nested() calls under
sv_lock as the worst case.

Assisted-by: LLM
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/nfsd/nfsctl.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index e5844d8454b8..66931caaaaed 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1992,21 +1992,22 @@ static bool nfsd_nl_transport_supported(const char *name)
 	return false;
 }
 
+/* Upper bound on the number of listeners a single request may carry. */
+#define NFSD_NL_LISTENER_MAX	1024
+
 /**
  * nfsd_nl_validate_listeners - sanity-check the listener list from userland
  * @info: netlink metadata and command arguments
  *
- * Walk every NFSD_A_SERVER_SOCK_ADDR attribute and confirm that each entry
- * is well-formed: it parses against the policy, carries both an address and
- * a supported transport name, and the address is long enough for its family.
- * Doing this up front lets the callers below assume every entry is valid and
- * guarantees we make no changes when the request is malformed.
+ * Walk every NFSD_A_SERVER_SOCK_ADDR attribute and confirm that the list is
+ * not oversized and that each entry is well-formed.
  *
  * Return: 0 if every entry is valid, or a negative errno otherwise.
  */
 static int nfsd_nl_validate_listeners(struct genl_info *info)
 {
 	const struct nlattr *attr;
+	unsigned int count = 0;
 	int rem;
 
 	nlmsg_for_each_attr_type(attr, NFSD_A_SERVER_SOCK_ADDR, info->nlhdr,
@@ -2015,6 +2016,11 @@ static int nfsd_nl_validate_listeners(struct genl_info *info)
 		struct sockaddr *sa;
 		int err;
 
+		if (++count > NFSD_NL_LISTENER_MAX) {
+			NL_SET_ERR_MSG(info->extack, "too many listeners");
+			return -E2BIG;
+		}
+
 		err = nla_parse_nested(tb, NFSD_A_SOCK_MAX, attr,
 				       nfsd_sock_nl_policy, info->extack);
 		if (err < 0)

-- 
2.55.0

[PATCH v2 3/8] SUNRPC: keep the first error in svc_register()

[Jeff Layton]

svc_register() assigns each pg_rpcbind_set() result to the same "error"
and returns the last one. The break only leaves the version loop, so any
program after a failed one overwrites its error.

Keep the first error instead of the last.

This is a flag day for CONFIG_NFS_LOCALIO=y, which converges on the
CONFIG_NFS_LOCALIO=n behaviour (the Kconfig default):

- NFSv4 is unaffected: nfsd_version4 sets vs_rpcb_optnl, so
  svc_generic_rpcbind_set() returns 0 for it however __svc_register() went.
- nfsd_version3 does not set it, and nfsd_net_init() enables every
  supported version, so a v3-enabled server with no reachable rpcbind now
  fails to bring up any listener. svc_bind() does not catch that earlier:
  rpcb_create_local() falls through to rpcb_create_local_net(), which
  passes RPC_CLNT_CREATE_NOPING and returns 0 with nothing listening.
- A partial failure (nfsd registered, nfsacl not) tears the listener down
  but leaves the nfsd entry in rpcbind until the next svc_rpcb_setup()
  clears it.

Fixes: 642ee6b209c2 ("SUNRPC: Allow further customisation of RPC program registration")
Assisted-by: LLM
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 net/sunrpc/svc.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 8297bad2b177..4f402bbf97ba 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -1208,13 +1208,16 @@ int svc_register(const struct svc_serv *serv, struct net *net,
 		struct svc_program *progp = &serv->sv_programs[p];
 
 		for (i = 0; i < progp->pg_nvers; i++) {
+			int ret;
 
-			error = progp->pg_rpcbind_set(net, progp, i,
+			ret = progp->pg_rpcbind_set(net, progp, i,
 					family, proto, port);
-			if (error < 0) {
+			if (ret < 0) {
 				printk(KERN_WARNING "svc: failed to register "
 					"%sv%u RPC service (errno %d).\n",
-					progp->pg_name, i, -error);
+					progp->pg_name, i, -ret);
+				if (!error)
+					error = ret;
 				break;
 			}
 		}

-- 
2.55.0

[PATCH v2 4/8] SUNRPC: undo partial rpcbind registrations when svc_register() fails

[Jeff Layton]

svc_register() registers each [program, version] in turn. On failure the
caller tears the listener down -- svc_setup_socket() frees the svc_sock and
svc_create_socket() releases the socket -- but the entries that were already
set stay in rpcbind, now pointing at a closed port. XPT_RPCB_UNREG is set
later, in svc_udp_init()/svc_tcp_init(), so svc_delete_xprt() never runs for
this transport and nothing clears them.

Unwind on failure, and stop the walk there rather than registering the
programs after it. rpcbind matches RPCBPROC_UNSET on
[program, version, netid] and ignores the address, so the unwind clears the
netid, not just the port -- the same granularity svc_delete_xprt() already
unregisters at.

Assisted-by: LLM
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 net/sunrpc/svc.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 4f402bbf97ba..9ffa87007004 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -1183,6 +1183,29 @@ int svc_generic_rpcbind_set(struct net *net,
 }
 EXPORT_SYMBOL_GPL(svc_generic_rpcbind_set);
 
+/*
+ * Undo the [program, version] registrations that this svc_register() call
+ * already made, stopping at version @nvers of program @nprog.
+ *
+ * Note that rpcbind matches RPCBPROC_UNSET on [program, version, netid] and
+ * ignores the address, so this clears the netid rather than the one port.
+ * That is the granularity svc_delete_xprt() unregisters at as well.
+ */
+static void svc_unwind_register(const struct svc_serv *serv, struct net *net,
+				const int family, const unsigned short proto,
+				unsigned int nprog, unsigned int nvers)
+{
+	unsigned int p, i;
+
+	for (p = 0; p <= nprog; p++) {
+		struct svc_program *progp = &serv->sv_programs[p];
+		unsigned int last = p < nprog ? progp->pg_nvers : nvers;
+
+		for (i = 0; i < last; i++)
+			progp->pg_rpcbind_set(net, progp, i, family, proto, 0);
+	}
+}
+
 /**
  * svc_register - register an RPC service with the local portmapper
  * @serv: svc_serv struct for the service to register
@@ -1191,7 +1214,8 @@ EXPORT_SYMBOL_GPL(svc_generic_rpcbind_set);
  * @proto: transport protocol number to advertise
  * @port: port to advertise
  *
- * Service is registered for any address in the passed-in protocol family
+ * Service is registered for any address in the passed-in protocol family.
+ * A @port of 0 unregisters instead, and then every program is attempted.
  */
 int svc_register(const struct svc_serv *serv, struct net *net,
 		 const int family, const unsigned short proto,
@@ -1216,6 +1240,11 @@ int svc_register(const struct svc_serv *serv, struct net *net,
 				printk(KERN_WARNING "svc: failed to register "
 					"%sv%u RPC service (errno %d).\n",
 					progp->pg_name, i, -ret);
+				if (port) {
+					svc_unwind_register(serv, net, family,
+							    proto, p, i);
+					return ret;
+				}
 				if (!error)
 					error = ret;
 				break;

-- 
2.55.0

Re: [PATCH v2 4/8] SUNRPC: undo partial rpcbind registrations when svc_register() fails

[Chuck Lever]

On Tue, Aug 11, 2026, at 8:03 AM, Jeff Layton wrote:
> svc_register() registers each [program, version] in turn. On failure the
> caller tears the listener down -- svc_setup_socket() frees the svc_sock and
> svc_create_socket() releases the socket -- but the entries that were already
> set stay in rpcbind, now pointing at a closed port. XPT_RPCB_UNREG is set
> later, in svc_udp_init()/svc_tcp_init(), so svc_delete_xprt() never runs for
> this transport and nothing clears them.
>
> Unwind on failure, and stop the walk there rather than registering the
> programs after it. rpcbind matches RPCBPROC_UNSET on
> [program, version, netid] and ignores the address, so the unwind clears the
> netid, not just the port -- the same granularity svc_delete_xprt() already
> unregisters at.
>
> Assisted-by: LLM
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>  net/sunrpc/svc.c | 31 ++++++++++++++++++++++++++++++-
>  1 file changed, 30 insertions(+), 1 deletion(-)
>
> diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
> index 4f402bbf97ba..9ffa87007004 100644
> --- a/net/sunrpc/svc.c
> +++ b/net/sunrpc/svc.c
> @@ -1183,6 +1183,29 @@ int svc_generic_rpcbind_set(struct net *net,
>  }
>  EXPORT_SYMBOL_GPL(svc_generic_rpcbind_set);
> 
> +/*
> + * Undo the [program, version] registrations that this svc_register() 
> call
> + * already made, stopping at version @nvers of program @nprog.
> + *
> + * Note that rpcbind matches RPCBPROC_UNSET on [program, version, 
> netid] and
> + * ignores the address, so this clears the netid rather than the one 
> port.
> + * That is the granularity svc_delete_xprt() unregisters at as well.
> + */
> +static void svc_unwind_register(const struct svc_serv *serv, struct 
> net *net,
> +				const int family, const unsigned short proto,
> +				unsigned int nprog, unsigned int nvers)
> +{
> +	unsigned int p, i;
> +
> +	for (p = 0; p <= nprog; p++) {
> +		struct svc_program *progp = &serv->sv_programs[p];
> +		unsigned int last = p < nprog ? progp->pg_nvers : nvers;
> +
> +		for (i = 0; i < last; i++)
> +			progp->pg_rpcbind_set(net, progp, i, family, proto, 0);
> +	}
> +}

For an IPv4 listener, the port-zero callback falls back through
__svc_rpcb_register4() to rpcb_register(). PMAPPROC_UNSET ignores
its protocol argument, so unwinding a partially successful TCP
registration also removes the mappings for existing listeners on
other transports, I would think.

It might be that the best the kernel can do here is tear everything
down if one registration fails.


-- 
Chuck Lever

Re: [PATCH v2 4/8] SUNRPC: undo partial rpcbind registrations when svc_register() fails

[Jeff Layton]

On Tue, 2026-08-11 at 15:19 -0400, Chuck Lever wrote:
> 
> On Tue, Aug 11, 2026, at 8:03 AM, Jeff Layton wrote:
> > svc_register() registers each [program, version] in turn. On failure the
> > caller tears the listener down -- svc_setup_socket() frees the svc_sock and
> > svc_create_socket() releases the socket -- but the entries that were already
> > set stay in rpcbind, now pointing at a closed port. XPT_RPCB_UNREG is set
> > later, in svc_udp_init()/svc_tcp_init(), so svc_delete_xprt() never runs for
> > this transport and nothing clears them.
> > 
> > Unwind on failure, and stop the walk there rather than registering the
> > programs after it. rpcbind matches RPCBPROC_UNSET on
> > [program, version, netid] and ignores the address, so the unwind clears the
> > netid, not just the port -- the same granularity svc_delete_xprt() already
> > unregisters at.
> > 
> > Assisted-by: LLM
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> >  net/sunrpc/svc.c | 31 ++++++++++++++++++++++++++++++-
> >  1 file changed, 30 insertions(+), 1 deletion(-)
> > 
> > diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
> > index 4f402bbf97ba..9ffa87007004 100644
> > --- a/net/sunrpc/svc.c
> > +++ b/net/sunrpc/svc.c
> > @@ -1183,6 +1183,29 @@ int svc_generic_rpcbind_set(struct net *net,
> >  }
> >  EXPORT_SYMBOL_GPL(svc_generic_rpcbind_set);
> > 
> > +/*
> > + * Undo the [program, version] registrations that this svc_register() 
> > call
> > + * already made, stopping at version @nvers of program @nprog.
> > + *
> > + * Note that rpcbind matches RPCBPROC_UNSET on [program, version, 
> > netid] and
> > + * ignores the address, so this clears the netid rather than the one 
> > port.
> > + * That is the granularity svc_delete_xprt() unregisters at as well.
> > + */
> > +static void svc_unwind_register(const struct svc_serv *serv, struct 
> > net *net,
> > +				const int family, const unsigned short proto,
> > +				unsigned int nprog, unsigned int nvers)
> > +{
> > +	unsigned int p, i;
> > +
> > +	for (p = 0; p <= nprog; p++) {
> > +		struct svc_program *progp = &serv->sv_programs[p];
> > +		unsigned int last = p < nprog ? progp->pg_nvers : nvers;
> > +
> > +		for (i = 0; i < last; i++)
> > +			progp->pg_rpcbind_set(net, progp, i, family, proto, 0);
> > +	}
> > +}
> 
> For an IPv4 listener, the port-zero callback falls back through
> __svc_rpcb_register4() to rpcb_register(). PMAPPROC_UNSET ignores
> its protocol argument, so unwinding a partially successful TCP
> registration also removes the mappings for existing listeners on
> other transports, I would think.
> 
> It might be that the best the kernel can do here is tear everything
> down if one registration fails.
> 

What I was thinking for NFSv2/3 was to just have the listener set
netlink call wait for registration to complete before returning to
userland. That would mean we'd have to block even longer to try and
unregister things if things fail.

Alternate proposal: let's just declare rpcbind reg errors to be non-
fatal: do a pr_warn() and just leave it up to the admin to sort it out
if that happens instead of trying to fail the startup.

The resulting situation for the server is no worse off (it's just
running instead of being down), and I move that we're better off
leaving it up to a human to clean up the mess instead of trying to fix
things up from the kernel.

Thoughts?
-- 
Jeff Layton <jlayton@kernel.org>

Re: [PATCH v2 4/8] SUNRPC: undo partial rpcbind registrations when svc_register() fails

[Chuck Lever]

On Wed, Aug 12, 2026, at 3:38 PM, Jeff Layton wrote:
> On Tue, 2026-08-11 at 15:19 -0400, Chuck Lever wrote:

>> For an IPv4 listener, the port-zero callback falls back through
>> __svc_rpcb_register4() to rpcb_register(). PMAPPROC_UNSET ignores
>> its protocol argument, so unwinding a partially successful TCP
>> registration also removes the mappings for existing listeners on
>> other transports, I would think.
>> 
>> It might be that the best the kernel can do here is tear everything
>> down if one registration fails.
>> 
>
> What I was thinking for NFSv2/3 was to just have the listener set
> netlink call wait for registration to complete before returning to
> userland. That would mean we'd have to block even longer to try and
> unregister things if things fail.
>
> Alternate proposal: let's just declare rpcbind reg errors to be non-
> fatal: do a pr_warn() and just leave it up to the admin to sort it out
> if that happens instead of trying to fail the startup.
>
> The resulting situation for the server is no worse off (it's just
> running instead of being down), and I move that we're better off
> leaving it up to a human to clean up the mess instead of trying to fix
> things up from the kernel.

I was thinking of this in terms of a declarative administrative UI:
If the kernel can't set the requested configuration, it should
fail back to the previous configuration. Maybe that's not possible.

On the other hand, what might be better is to handle the rpcbind
registration from user space instead of the kernel, after the
kernel listener is set up.


-- 
Chuck Lever

Re: [PATCH v2 4/8] SUNRPC: undo partial rpcbind registrations when svc_register() fails

[Jeff Layton]

On Wed, 2026-08-12 at 15:57 -0400, Chuck Lever wrote:
> 
> On Wed, Aug 12, 2026, at 3:38 PM, Jeff Layton wrote:
> > On Tue, 2026-08-11 at 15:19 -0400, Chuck Lever wrote:
> 
> > > For an IPv4 listener, the port-zero callback falls back through
> > > __svc_rpcb_register4() to rpcb_register(). PMAPPROC_UNSET ignores
> > > its protocol argument, so unwinding a partially successful TCP
> > > registration also removes the mappings for existing listeners on
> > > other transports, I would think.
> > > 
> > > It might be that the best the kernel can do here is tear everything
> > > down if one registration fails.
> > > 
> > 
> > What I was thinking for NFSv2/3 was to just have the listener set
> > netlink call wait for registration to complete before returning to
> > userland. That would mean we'd have to block even longer to try and
> > unregister things if things fail.
> > 
> > Alternate proposal: let's just declare rpcbind reg errors to be non-
> > fatal: do a pr_warn() and just leave it up to the admin to sort it out
> > if that happens instead of trying to fail the startup.
> > 
> > The resulting situation for the server is no worse off (it's just
> > running instead of being down), and I move that we're better off
> > leaving it up to a human to clean up the mess instead of trying to fix
> > things up from the kernel.
> 
> I was thinking of this in terms of a declarative administrative UI:
> If the kernel can't set the requested configuration, it should
> fail back to the previous configuration. Maybe that's not possible.
> 

It's possible, but difficult. The original /proc interfaces were never
this clean, so making the underlying bits behave this way for the
netlink interfaces, but not the legacy /proc ones will be hard.

Also, today we don't take any steps to try and preserve the old
listener table. That would have to be done here as well.

> On the other hand, what might be better is to handle the rpcbind
> registration from user space instead of the kernel, after the
> kernel listener is set up.
> 

That's possible I guess. We could send a new boolean down in the
listener call that says "don't do any rpcbind registration" and then if
the kernel indicates that it understands that message then userland
could do the registration.

That's a major undertaking though and I don't like fundamentally
changing the interface here, particularly when we'll still have to cope
with doing this from the kernel for legacy cases.

I still think the best solution of all would be to just say
"henceforth, rpcbind registration is non-fatal". That just leaves the
kernel succeeding the listener set today when it would have failed
before, but will still printk() an appropriate warning in that case, so
the admin should be aware that rpcbind registration failed, even though
the server is up.

Right now, I'm really unclear on what sort of changes you want to see
here as a final patchset. What would make this mergeable for you?
-- 
Jeff Layton <jlayton@kernel.org>

Re: [PATCH v2 4/8] SUNRPC: undo partial rpcbind registrations when svc_register() fails

[Chuck Lever]

On Fri, Aug 14, 2026, at 7:01 AM, Jeff Layton wrote:
> I still think the best solution of all would be to just say
> "henceforth, rpcbind registration is non-fatal".

Fair enough, let's go with that.


> Right now, I'm really unclear on what sort of changes you want to see
> here as a final patchset. What would make this mergeable for you?

Sorry for the ambiguity. For the re-roll:

- 1, 2, 3 and 5 don't need change.

- Let's drop patch 4/8.

- Make registration failure non-fatal for NFSv2 and NFSv3, as
  proposed.
  
- Extend the extack in 6/8 to report a listener that came up without
  registering. dmesg is the only channel write_ports() has. Perhaps
  the netlink path can do better?

- Fix the netns leak in 8/8.

- Ensure that any test that asserts the unwind or the abort is moved
  over to the new failure policy.

HTH.

-- 
Chuck Lever

[PATCH v2 5/8] SUNRPC: bound the local rpcbind client timeout to 1s

[Jeff Layton]

The kernel's local rpcbind client runs on the transport defaults: a 10s
major timeout for AF_LOCAL, 60s for the loopback TCP fallback
(xprt_calc_majortimeo() returns to_initval when to_increment is 0).

Those calls are synchronous and run under nfsd_mutex, several per
operation: rpcb_create_local() attempts up to three client creations, and
svc_register() issues one call per program and version. A local rpcbind
that accepts the connection but never replies stalls each of them, and
the accumulated hold is enough to trip the hung-task watchdog on other
NFSD netlink ops (the holder waits killably and evades it):

  INFO: task hung in nfsd_nl_cache_flush_doit

The local rpcbind lives on loopback or an AF_LOCAL socket and answers in
microseconds, so bound its client to one attempt, 1s.

This shortens the stall rather than removing it, and it is not free.
Registration stays synchronous and stays fatal: rpcb_create_local()
failure aborts nfsd_create_serv() via svc_bind(), and svc_register()
failure makes svc_setup_socket() fail, so a rpcbind that is merely slow
to be scheduled can now fail server startup where it previously
succeeded. Making the registration asynchronous is the real fix.

Assisted-by: LLM
Link: https://syzkaller.appspot.com/bug?extid=c7eae0eb80858a2dba0f
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 net/sunrpc/rpcb_clnt.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/net/sunrpc/rpcb_clnt.c b/net/sunrpc/rpcb_clnt.c
index 6aa372188c86..0aa376b82a52 100644
--- a/net/sunrpc/rpcb_clnt.c
+++ b/net/sunrpc/rpcb_clnt.c
@@ -221,6 +221,16 @@ static void rpcb_set_local(struct net *net, struct rpc_clnt *clnt,
 # define SUN_LEN(ptr) (offsetof(struct sockaddr_un, sun_path)		\
 		      + 1 + strlen((ptr)->sun_path + 1))
 
+/*
+ * The kernel's rpcbind client talks only to the local rpcbind, over loopback
+ * or a local AF_LOCAL socket, where a healthy rpcbind answers in microseconds.
+ */
+static const struct rpc_timeout rpcb_local_timeout = {
+	.to_initval	= 1 * HZ,
+	.to_maxval	= 1 * HZ,
+	.to_retries	= 0,
+};
+
 /*
  * Returns zero on success, otherwise a negative errno value
  * is returned.
@@ -238,6 +248,7 @@ static int rpcb_create_af_local(struct net *net,
 		.version	= RPCBVERS_2,
 		.authflavor	= RPC_AUTH_NULL,
 		.cred		= current_cred(),
+		.timeout	= &rpcb_local_timeout,
 		/*
 		 * We turn off the idle timeout to prevent the kernel
 		 * from automatically disconnecting the socket.
@@ -312,6 +323,7 @@ static int rpcb_create_local_net(struct net *net)
 		.version	= RPCBVERS_2,
 		.authflavor	= RPC_AUTH_UNIX,
 		.cred		= current_cred(),
+		.timeout	= &rpcb_local_timeout,
 		.flags		= RPC_CLNT_CREATE_NOPING,
 	};
 	struct rpc_clnt *clnt, *clnt4;

-- 
2.55.0

[PATCH v2 6/8] NFSD: report listener creation failures through extack

[Jeff Layton]

nfsd_nl_listener_set_doit() hands back the raw errno from
svc_xprt_create_from_sa() and sets no extack, so a failed LISTENER_SET
tells userland only "Connection refused". The usual cause is
svc_setup_socket() -> svc_register() failing because the local rpcbind is
not reachable, which is not guessable from the errno alone -- and since
"SUNRPC: keep the first error in svc_register()" that failure is fatal on
CONFIG_NFS_LOCALIO=y too.

Name the transport and the error. The message tracks err, which keeps the
last failure, so a multi-listener request reports the entry whose errno is
returned.

The rejections in nfsd_nl_validate_listeners() other than -E2BIG are still
bare; those are left alone here.

Assisted-by: LLM
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/nfsd/nfsctl.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 66931caaaaed..a6ef85e6b419 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -2184,8 +2184,12 @@ int nfsd_nl_listener_set_doit(struct sk_buff *skb, struct genl_info *info)
 		ret = svc_xprt_create_from_sa(serv, xcl_name, net, sa, 0,
 					      current_cred());
 		/* always save the latest error */
-		if (ret < 0)
+		if (ret < 0) {
+			NL_SET_ERR_MSG_FMT(info->extack,
+					   "cannot create %s listener: %d",
+					   xcl_name, ret);
 			err = ret;
+		}
 	}
 
 	if (!serv->sv_nrthreads && list_empty(&nn->nfsd_serv->sv_permsocks))

-- 
2.55.0

[PATCH v2 7/8] selftests/nfsd: exercise listener_set request validation

[Jeff Layton]

Regression tests for the NFSD_CMD_LISTENER_SET checks that
nfsd_nl_validate_listeners() runs before nfsd_mutex is taken: bad or absent
transport name, missing address, truncated or unsupported sockaddr, bad
address family, a malformed entry behind a well-formed one, and more than
NFSD_NL_LISTENER_MAX entries. Plus a LISTENER_GET against an empty netns.

None of these reach nfsd_create_serv(), so nothing here creates a serv or
registers with rpcbind. Tests that do need one come next, with a stub.

Uses kselftest_harness.h so each test runs in its own net+mount namespace.
/run is masked there: unix_find_bsd() resolves by inode and takes no struct
net, so a "/var/run/rpcbind.sock" connect from this netns would otherwise
reach the rpcbind on the host -- and svc_rpcb_setup() opens by calling
svc_unregister(), which would clear the host's nfsd registrations.

The config fragment therefore has to cover the fixture as well as nfsd:
NAMESPACES and NET_NS for the unshare(), SHMEM and TMPFS for the mask, and
UNIX for the AF_LOCAL rpcbind client. Without them every test skips.

Assisted-by: LLM
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 tools/testing/selftests/Makefile                   |   1 +
 tools/testing/selftests/nfsd/.gitignore            |   1 +
 tools/testing/selftests/nfsd/Makefile              |   6 +
 tools/testing/selftests/nfsd/config                |   8 +
 .../testing/selftests/nfsd/nfsd_netlink_listener.c | 488 +++++++++++++++++++++
 tools/testing/selftests/nfsd/settings              |   1 +
 6 files changed, 505 insertions(+)

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 8d4db2241cc2..5d615301d368 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -85,6 +85,7 @@ TARGETS += net/packetdrill
 TARGETS += net/ppp
 TARGETS += net/rds
 TARGETS += net/tcp_ao
+TARGETS += nfsd
 TARGETS += nolibc
 TARGETS += pci_endpoint
 TARGETS += pcie_bwctrl
diff --git a/tools/testing/selftests/nfsd/.gitignore b/tools/testing/selftests/nfsd/.gitignore
new file mode 100644
index 000000000000..19e6dec04d8e
--- /dev/null
+++ b/tools/testing/selftests/nfsd/.gitignore
@@ -0,0 +1 @@
+nfsd_netlink_listener
diff --git a/tools/testing/selftests/nfsd/Makefile b/tools/testing/selftests/nfsd/Makefile
new file mode 100644
index 000000000000..15ac65549d25
--- /dev/null
+++ b/tools/testing/selftests/nfsd/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+CFLAGS += $(KHDR_INCLUDES) -Wall
+
+TEST_GEN_PROGS := nfsd_netlink_listener
+
+include ../lib.mk
diff --git a/tools/testing/selftests/nfsd/config b/tools/testing/selftests/nfsd/config
new file mode 100644
index 000000000000..ab84523fbedf
--- /dev/null
+++ b/tools/testing/selftests/nfsd/config
@@ -0,0 +1,8 @@
+CONFIG_NAMESPACES=y
+CONFIG_NET_NS=y
+CONFIG_SHMEM=y
+CONFIG_TMPFS=y
+CONFIG_UNIX=y
+CONFIG_IPV6=y
+CONFIG_NFSD=y
+CONFIG_NFSD_V4=y
diff --git a/tools/testing/selftests/nfsd/nfsd_netlink_listener.c b/tools/testing/selftests/nfsd/nfsd_netlink_listener.c
new file mode 100644
index 000000000000..ae28c224255f
--- /dev/null
+++ b/tools/testing/selftests/nfsd/nfsd_netlink_listener.c
@@ -0,0 +1,488 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Regression tests for the NFSD generic-netlink listener interface
+ * (NFSD_CMD_LISTENER_SET / NFSD_CMD_LISTENER_GET).
+ *
+ * These cover the request validation that nfsd_nl_validate_listeners() does
+ * before nfsd_mutex is taken: bad or absent transport name, missing address,
+ * truncated or unsupported sockaddr, oversized list. None of them reach
+ * nfsd_create_serv(), so nothing here creates a serv or talks to rpcbind.
+ *
+ * Each test runs in its own private net + mount namespace (unshare in
+ * FIXTURE_SETUP). /run is masked there: a pathname AF_LOCAL connect is not
+ * scoped by the network namespace, since unix_find_bsd() resolves by inode
+ * and takes no struct net, so the kernel's rpcbind client would otherwise be
+ * able to reach the rpcbind running on the host.
+ */
+#define _GNU_SOURCE
+#include <errno.h>
+#include <sched.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/mount.h>
+#include <sys/socket.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <sys/time.h>
+#include <net/if.h>
+#include <netinet/in.h>
+#include <linux/netlink.h>
+#include <linux/genetlink.h>
+
+#include "../kselftest_harness.h"
+
+/* NFSD generic-netlink constants (from linux/nfsd_netlink.h). */
+#define NFSD_FAMILY_NAME		"nfsd"
+#define NFSD_CMD_LISTENER_SET		6
+#define NFSD_CMD_LISTENER_GET		7
+#define NFSD_A_SERVER_SOCK_ADDR		1	/* per-listener nest */
+#define NFSD_A_SOCK_ADDR		1	/* inside the nest */
+#define NFSD_A_SOCK_TRANSPORT_NAME	2	/* inside the nest */
+
+#define NLA_ALIGN4(len)			(((len) + 3) & ~3)
+#define TEST_PORT			20049
+#define MAX_LISTENERS			8
+#define RECV_TIMEO_SEC			30
+
+static int nfsd_family;			/* set per-test in FIXTURE_SETUP */
+
+static void die(const char *msg)
+{
+	perror(msg);
+	exit(1);
+}
+
+/* ------------------- minimal generic-netlink plumbing ------------------- */
+
+static int genl_open(void)
+{
+	struct sockaddr_nl sa = { .nl_family = AF_NETLINK };
+	struct timeval tv = { .tv_sec = RECV_TIMEO_SEC };
+	int fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_GENERIC);
+
+	if (fd < 0)
+		die("socket(NETLINK_GENERIC)");
+	if (bind(fd, (void *)&sa, sizeof(sa)) < 0)
+		die("bind(netlink)");
+	setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
+	return fd;
+}
+
+/* Append an attribute at @off; return the new (aligned) offset. */
+static int put_attr(char *buf, int off, uint16_t type,
+		    const void *data, int len)
+{
+	struct nlattr *na = (void *)(buf + off);
+
+	na->nla_type = type;
+	na->nla_len = NLA_HDRLEN + len;
+	if (len)
+		memcpy(buf + off + NLA_HDRLEN, data, len);
+	return off + NLA_ALIGN4(NLA_HDRLEN + len);
+}
+
+/* Build a genl message header into @buf; return the offset past it. */
+static int genl_hdr(char *buf, uint16_t type, uint16_t flags, uint8_t cmd)
+{
+	struct nlmsghdr *nlh = (void *)buf;
+	struct genlmsghdr *gnl = (void *)(buf + NLMSG_HDRLEN);
+
+	memset(buf, 0, NLMSG_HDRLEN + GENL_HDRLEN);
+	nlh->nlmsg_type = type;
+	nlh->nlmsg_flags = flags;
+	nlh->nlmsg_seq = 1;
+	gnl->cmd = cmd;
+	gnl->version = 1;
+	return NLMSG_HDRLEN + GENL_HDRLEN;
+}
+
+/* Send an nfsd command with an ACK; return the ACK errno (<= 0). */
+static int genl_request(uint8_t cmd, const char *attrs, int attrs_len)
+{
+	char buf[1 << 20], rbuf[4096];
+	struct nlmsghdr *nlh = (void *)buf;
+	int fd = genl_open();
+	int off, n, ret;
+
+	off = genl_hdr(buf, nfsd_family, NLM_F_REQUEST | NLM_F_ACK, cmd);
+	if (attrs_len) {
+		memcpy(buf + off, attrs, attrs_len);
+		off += attrs_len;
+	}
+	nlh->nlmsg_len = off;
+
+	if (send(fd, buf, off, 0) < 0)
+		die("send(genl)");
+
+	n = recv(fd, rbuf, sizeof(rbuf), 0);
+	if (n < 0)
+		ret = (errno == EAGAIN || errno == EWOULDBLOCK) ? -ETIMEDOUT : -errno;
+	else if (((struct nlmsghdr *)rbuf)->nlmsg_type == NLMSG_ERROR)
+		ret = ((struct nlmsgerr *)NLMSG_DATA(rbuf))->error;
+	else
+		ret = 0;
+	close(fd);
+	return ret;
+}
+
+/* Send a command and return the full reply message; -errno on failure. */
+static int genl_request_reply(uint8_t cmd, char *rbuf, size_t rlen)
+{
+	char buf[256];
+	struct nlmsghdr *nlh = (void *)buf;
+	int fd = genl_open();
+	int off, n, ret;
+
+	off = genl_hdr(buf, nfsd_family, NLM_F_REQUEST, cmd);
+	nlh->nlmsg_len = off;
+
+	if (send(fd, buf, off, 0) < 0)
+		die("send(genl reply)");
+
+	n = recv(fd, rbuf, rlen, 0);
+	if (n < 0)
+		ret = (errno == EAGAIN || errno == EWOULDBLOCK) ? -ETIMEDOUT : -errno;
+	else if (((struct nlmsghdr *)rbuf)->nlmsg_type == NLMSG_ERROR)
+		ret = ((struct nlmsgerr *)NLMSG_DATA(rbuf))->error;
+	else
+		ret = n;
+	close(fd);
+	return ret;
+}
+
+/* Resolve the "nfsd" genl family id; -1 if not registered. */
+static int genl_resolve_nfsd(void)
+{
+	char buf[1024], rbuf[4096];
+	struct nlmsghdr *nlh = (void *)buf;
+	struct nlmsghdr *rh = (void *)rbuf;
+	struct nlattr *na;
+	int fd, off, left, id = -1;
+
+	fd = genl_open();
+	off = genl_hdr(buf, GENL_ID_CTRL, NLM_F_REQUEST, CTRL_CMD_GETFAMILY);
+	off = put_attr(buf, off, CTRL_ATTR_FAMILY_NAME,
+		       NFSD_FAMILY_NAME, sizeof(NFSD_FAMILY_NAME));
+	nlh->nlmsg_len = off;
+
+	if (send(fd, buf, off, 0) < 0)
+		die("send(GETFAMILY)");
+	if (recv(fd, rbuf, sizeof(rbuf), 0) < 0)
+		die("recv(GETFAMILY)");
+	close(fd);
+
+	if (rh->nlmsg_type == NLMSG_ERROR)
+		return -1;
+
+	na = (void *)((char *)NLMSG_DATA(rh) + GENL_HDRLEN);
+	left = rh->nlmsg_len - NLMSG_HDRLEN - GENL_HDRLEN;
+	while (left >= (int)NLA_HDRLEN) {
+		if (na->nla_type == CTRL_ATTR_FAMILY_ID) {
+			id = *(uint16_t *)((char *)na + NLA_HDRLEN);
+			break;
+		}
+		left -= NLA_ALIGN4(na->nla_len);
+		na = (void *)((char *)na + NLA_ALIGN4(na->nla_len));
+	}
+	return id;
+}
+
+/* ------------------- listener request builders ------------------- */
+
+/* Fine-grained control for negative tests: any field can be omitted/malformed. */
+struct raw_listener {
+	const char *xprt;	/* NULL -> omit NFSD_A_SOCK_TRANSPORT_NAME */
+	int emit_addr;		/* 0 -> omit NFSD_A_SOCK_ADDR */
+	const void *addr;
+	int addr_len;		/* bytes to emit for NFSD_A_SOCK_ADDR */
+};
+
+static int put_raw_listener(char *buf, int off, const struct raw_listener *r)
+{
+	struct nlattr *nest = (void *)(buf + off);
+	int inner = off + NLA_HDRLEN;
+
+	if (r->emit_addr)
+		inner = put_attr(buf, inner, NFSD_A_SOCK_ADDR, r->addr, r->addr_len);
+	if (r->xprt)
+		inner = put_attr(buf, inner, NFSD_A_SOCK_TRANSPORT_NAME,
+				 r->xprt, strlen(r->xprt) + 1);
+	nest->nla_type = NFSD_A_SERVER_SOCK_ADDR | NLA_F_NESTED;
+	nest->nla_len = inner - off;
+	return off + NLA_ALIGN4(nest->nla_len);
+}
+
+/* Well-formed loopback listener for @family (AF_INET or AF_INET6). */
+static int put_listener_af(char *buf, int off, const char *xprt, int family,
+			   uint16_t port)
+{
+	struct sockaddr_storage ss = {0};
+	struct raw_listener r = { .xprt = xprt, .emit_addr = 1, .addr = &ss };
+
+	if (family == AF_INET6) {
+		struct sockaddr_in6 *s6 = (void *)&ss;
+
+		s6->sin6_family = AF_INET6;
+		s6->sin6_port = htons(port);
+		s6->sin6_addr = in6addr_loopback;
+		r.addr_len = sizeof(*s6);
+	} else {
+		struct sockaddr_in *s4 = (void *)&ss;
+
+		s4->sin_family = AF_INET;
+		s4->sin_port = htons(port);
+		s4->sin_addr.s_addr = htonl(INADDR_LOOPBACK);
+		r.addr_len = sizeof(*s4);
+	}
+	return put_raw_listener(buf, off, &r);
+}
+
+static int put_listener(char *buf, int off, const char *xprt, uint16_t port)
+{
+	return put_listener_af(buf, off, xprt, AF_INET, port);
+}
+
+/* ------------------- LISTENER_GET parsing ------------------- */
+
+struct listener_ent {
+	char xprt[16];
+	int family;
+	uint16_t port;
+	struct in_addr a4;
+	struct in6_addr a6;
+};
+
+static int parse_listener_get(const char *rbuf, int len,
+			      struct listener_ent *out, int max)
+{
+	const struct nlmsghdr *nlh = (const void *)rbuf;
+	const struct nlattr *na;
+	int left, count = 0;
+
+	(void)len;
+	na = (const void *)(rbuf + NLMSG_HDRLEN + GENL_HDRLEN);
+	left = nlh->nlmsg_len - NLMSG_HDRLEN - GENL_HDRLEN;
+
+	while (left >= (int)NLA_HDRLEN) {
+		int alen = na->nla_len;
+
+		if ((na->nla_type & NLA_TYPE_MASK) == NFSD_A_SERVER_SOCK_ADDR &&
+		    count < max) {
+			const struct nlattr *in = (const void *)((char *)na + NLA_HDRLEN);
+			int ileft = alen - NLA_HDRLEN;
+			struct listener_ent *e = &out[count];
+
+			memset(e, 0, sizeof(*e));
+			while (ileft >= (int)NLA_HDRLEN) {
+				const void *d = (const char *)in + NLA_HDRLEN;
+				int t = in->nla_type & NLA_TYPE_MASK;
+
+				if (t == NFSD_A_SOCK_TRANSPORT_NAME) {
+					strncpy(e->xprt, d, sizeof(e->xprt) - 1);
+				} else if (t == NFSD_A_SOCK_ADDR) {
+					const struct sockaddr_storage *ss = d;
+
+					e->family = ss->ss_family;
+					if (ss->ss_family == AF_INET) {
+						const struct sockaddr_in *s = d;
+
+						e->a4 = s->sin_addr;
+						e->port = ntohs(s->sin_port);
+					} else if (ss->ss_family == AF_INET6) {
+						const struct sockaddr_in6 *s = d;
+
+						e->a6 = s->sin6_addr;
+						e->port = ntohs(s->sin6_port);
+					}
+				}
+				ileft -= NLA_ALIGN4(in->nla_len);
+				in = (const void *)((char *)in + NLA_ALIGN4(in->nla_len));
+			}
+			count++;
+		}
+		left -= NLA_ALIGN4(alen);
+		na = (const void *)((char *)na + NLA_ALIGN4(alen));
+	}
+	return count;
+}
+
+/* ------------------- convenience wrappers ------------------- */
+
+static int listener_set(const char *attrs, int len)
+{
+	return genl_request(NFSD_CMD_LISTENER_SET, attrs, len);
+}
+
+/* Fetch the current listeners; returns count (>=0) or -errno. */
+static int listener_get(struct listener_ent *out, int max)
+{
+	char rbuf[8192];
+	int n = genl_request_reply(NFSD_CMD_LISTENER_GET, rbuf, sizeof(rbuf));
+
+	if (n < 0)
+		return n;
+	return parse_listener_get(rbuf, n, out, max);
+}
+
+/* --------------------------- fixture --------------------------- */
+
+FIXTURE(nfsd_listener) {
+	int placeholder;
+};
+
+FIXTURE_SETUP(nfsd_listener)
+{
+	struct ifreq ifr = {0};
+	struct stat st;
+	int s;
+
+	if (geteuid() != 0)
+		SKIP(return, "must be run as root");
+	if (unshare(CLONE_NEWNET | CLONE_NEWNS) < 0)
+		SKIP(return, "unshare(NEWNET|NEWNS): %s", strerror(errno));
+	if (mount("", "/", NULL, MS_REC | MS_PRIVATE, NULL) < 0)
+		SKIP(return, "mount(/ private): %s", strerror(errno));
+
+	/*
+	 * Keep the kernel's rpcbind client inside this namespace. The
+	 * abstract socket it tries first is per-netns, but the
+	 * "/var/run/rpcbind.sock" fallback is not, so hide the path.
+	 */
+	if (mount("tmpfs", "/run", "tmpfs", 0, NULL) < 0)
+		SKIP(return, "mount(tmpfs on /run): %s", strerror(errno));
+	if (lstat("/var/run", &st) == 0 && S_ISDIR(st.st_mode) &&
+	    mount("tmpfs", "/var/run", "tmpfs", 0, NULL) < 0)
+		SKIP(return, "mount(tmpfs on /var/run): %s", strerror(errno));
+
+	/* Bring loopback up so listener binds (127.0.0.1 / ::1) work. */
+	s = socket(AF_INET, SOCK_DGRAM, 0);
+	ASSERT_GE(s, 0);
+	strcpy(ifr.ifr_name, "lo");
+	ASSERT_EQ(0, ioctl(s, SIOCGIFFLAGS, &ifr));
+	ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
+	ASSERT_EQ(0, ioctl(s, SIOCSIFFLAGS, &ifr));
+	close(s);
+
+	nfsd_family = genl_resolve_nfsd();
+	if (nfsd_family < 0)
+		SKIP(return, "nfsd genl family not found (modprobe nfsd?)");
+}
+
+FIXTURE_TEARDOWN(nfsd_listener)
+{
+}
+
+/* ===================== validation / negative ===================== */
+
+TEST_F(nfsd_listener, val_too_many)
+{
+	static char attrs[1 << 20];
+	int i, off = 0;
+
+	for (i = 0; i < 1025; i++)		/* > NFSD_NL_LISTENER_MAX (1024) */
+		off = put_listener(attrs, off, "udp", TEST_PORT);
+	EXPECT_EQ(-E2BIG, listener_set(attrs, off));
+}
+
+TEST_F(nfsd_listener, val_missing_addr)
+{
+	char attrs[64];
+	struct raw_listener r = { .xprt = "tcp", .emit_addr = 0 };
+	int off = put_raw_listener(attrs, 0, &r);
+
+	EXPECT_EQ(-EINVAL, listener_set(attrs, off));
+}
+
+TEST_F(nfsd_listener, val_missing_transport)
+{
+	struct sockaddr_in s4 = { .sin_family = AF_INET, .sin_port = htons(TEST_PORT) };
+	struct raw_listener r = { .xprt = NULL, .emit_addr = 1,
+				  .addr = &s4, .addr_len = sizeof(s4) };
+	char attrs[64];
+	int off = put_raw_listener(attrs, 0, &r);
+
+	EXPECT_EQ(-EINVAL, listener_set(attrs, off));
+}
+
+/*
+ * A name matching no transport class must be refused before nfsd_mutex is
+ * taken, so it never reaches svc_xprt_create_from_sa() and its
+ * request_module("svc%s", name) upcall.
+ */
+TEST_F(nfsd_listener, val_bad_transport)
+{
+	char attrs[64];
+	int off = put_listener(attrs, 0, "bogus_xprt", TEST_PORT);
+
+	EXPECT_EQ(-EPROTONOSUPPORT, listener_set(attrs, off));
+}
+
+TEST_F(nfsd_listener, val_addr_too_short)
+{
+	unsigned char tiny = 0;
+	struct raw_listener r = { .xprt = "tcp", .emit_addr = 1,
+				  .addr = &tiny, .addr_len = 1 };
+	char attrs[64];
+	int off = put_raw_listener(attrs, 0, &r);
+
+	EXPECT_EQ(-EINVAL, listener_set(attrs, off));
+}
+
+TEST_F(nfsd_listener, val_inet_short)
+{
+	struct sockaddr_in s4 = { .sin_family = AF_INET, .sin_port = htons(TEST_PORT) };
+	struct raw_listener r = { .xprt = "tcp", .emit_addr = 1, .addr = &s4,
+				  .addr_len = sizeof(sa_family_t) + 2 };
+	char attrs[64];
+	int off = put_raw_listener(attrs, 0, &r);
+
+	EXPECT_EQ(-EINVAL, listener_set(attrs, off));
+}
+
+TEST_F(nfsd_listener, val_inet6_short)
+{
+	struct sockaddr_in6 s6 = { .sin6_family = AF_INET6, .sin6_port = htons(TEST_PORT) };
+	struct raw_listener r = { .xprt = "tcp", .emit_addr = 1, .addr = &s6,
+				  .addr_len = sizeof(struct sockaddr_in) };
+	char attrs[64];
+	int off = put_raw_listener(attrs, 0, &r);
+
+	EXPECT_EQ(-EINVAL, listener_set(attrs, off));
+}
+
+TEST_F(nfsd_listener, val_bad_family)
+{
+	struct sockaddr_storage ss = { .ss_family = AF_UNIX };
+	struct raw_listener r = { .xprt = "tcp", .emit_addr = 1, .addr = &ss,
+				  .addr_len = sizeof(struct sockaddr_in) };
+	char attrs[64];
+	int off = put_raw_listener(attrs, 0, &r);
+
+	EXPECT_EQ(-EAFNOSUPPORT, listener_set(attrs, off));
+}
+
+TEST_F(nfsd_listener, val_second_entry_bad)
+{
+	struct sockaddr_storage ss = { .ss_family = AF_UNIX };
+	struct raw_listener bad = { .xprt = "tcp", .emit_addr = 1, .addr = &ss,
+				    .addr_len = sizeof(struct sockaddr_in) };
+	char attrs[128];
+	int off = put_listener(attrs, 0, "tcp", TEST_PORT);
+
+	off = put_raw_listener(attrs, off, &bad);
+	/* The whole request is rejected during validation; nothing applied. */
+	EXPECT_EQ(-EAFNOSUPPORT, listener_set(attrs, off));
+}
+
+/* LISTENER_GET with no serv in this netns returns an empty list. */
+TEST_F(nfsd_listener, func_get_empty)
+{
+	struct listener_ent got[MAX_LISTENERS];
+
+	EXPECT_EQ(0, listener_get(got, MAX_LISTENERS));
+}
+
+TEST_HARNESS_MAIN
diff --git a/tools/testing/selftests/nfsd/settings b/tools/testing/selftests/nfsd/settings
new file mode 100644
index 000000000000..6091b45d226b
--- /dev/null
+++ b/tools/testing/selftests/nfsd/settings
@@ -0,0 +1 @@
+timeout=120

-- 
2.55.0

[PATCH v2 8/8] selftests/nfsd: add a per-netns rpcbind stub and the listener round-trips

[Jeff Layton]

Creating a listener registers with rpcbind: svc_xprt_create_from_sa() passes
flags of 0, so pmap_register is true in svc_setup_socket(), and
nfsd_version3 is enabled by default and does not set vs_rpcb_optnl, so a
registration failure aborts listener creation. A fresh netns has no rpcbind,
and reaching the host's is not an option -- svc_rpcb_setup() opens by
calling svc_unregister(), which would clear the host's nfsd entries.

Serve it from within the namespace instead. The abstract AF_LOCAL name the
kernel tries first is per-netns (unix_find_abstract() takes a struct net),
so bind "\0/run/rpcbind.sock" and fork a minimal responder:

- arguments are never decoded; the NULL procedure gets an empty success and
  SET/UNSET get TRUE
- RPCBVERS_4 is answered as well as RPCBVERS_2, because
  __svc_rpcb_register6() turns a v4 refusal into -EAFNOSUPPORT and that
  would fail every IPv6 listener
- connections accepted and calls answered are counted in a page shared with
  the test
- PR_SET_PDEATHSIG plus an explicit kill in FIXTURE_TEARDOWN, so no stub
  outlives its test

With that in place, add the tests that need a serv: create/add/remove and
LISTENER_GET round-trips (tcp, udp, multi, idempotent re-set, subset
removal, empty-list serv destroy, IPv6), the empty-list request, and the
-EBUSY refusal once THREADS_SET has started threads.

Several of these exist to catch a revert rather than to describe the
interface, since none of them is visible in the errno alone:

- val_reject_keeps_listeners. An unknown transport name ends in
  -EPROTONOSUPPORT either way, because svc_xprt_create_from_sa() returns
  that too. What differs is that without the up-front check
  nfsd_nl_listener_set_doit() has already destroyed the listeners that did
  not match by the time the name fails.
- val_bad_transport, extended to require that the stub saw no traffic.
  Reaching svc_xprt_create_from_sa() means nfsd_create_serv() ran, and
  svc_bind() pings rpcbind at client creation and then sweeps stale entries
  with svc_unregister(), so silence is what shows the request was refused
  up front.
- val_second_entry_bad, extended with a LISTENER_GET. -EAFNOSUPPORT is
  also what svc_xprt_create_from_sa() returns for the bad entry, and the
  doit keeps the listeners it did create, so the well-formed tcp entry
  ahead of it would otherwise still be up.
- sem_register_refused, which restarts the stub in a mode that answers
  RPCBPROC_SET with FALSE. rpcb_register_call() turns that into -EACCES,
  which must reach userland and leave no listener behind. On
  CONFIG_NFS_LOCALIO=y it does not, unless svc_register() keeps the first
  error: nfslocalio is last in nfsd_programs and its NULL and vs_hidden
  versions both report success, overwriting the failure.
- func_empty_destroys uses the connection count. LISTENER_GET replies empty
  for a destroyed serv and for a live one with no permsocks alike, but only
  nfsd_destroy_serv() reaches svc_xprt_destroy_all(..., unregister=true) ->
  svc_rpcb_cleanup() -> rpcb_put_local(), which drops the last user and
  shuts the local client down. The next serv has to reconnect.
- sem_busy_on_change and sem_busy_on_remove read the listeners back, since
  -EBUSY says nothing about what the doit did before it returned.

find_listener() matches the address as well as the transport, family and
port; every listener here is created on loopback, so a reply naming
0.0.0.0 has to fail.

Assisted-by: LLM
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 .../testing/selftests/nfsd/nfsd_netlink_listener.c | 554 ++++++++++++++++++++-
 1 file changed, 548 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/nfsd/nfsd_netlink_listener.c b/tools/testing/selftests/nfsd/nfsd_netlink_listener.c
index ae28c224255f..9972b0db45ff 100644
--- a/tools/testing/selftests/nfsd/nfsd_netlink_listener.c
+++ b/tools/testing/selftests/nfsd/nfsd_netlink_listener.c
@@ -3,30 +3,41 @@
  * Regression tests for the NFSD generic-netlink listener interface
  * (NFSD_CMD_LISTENER_SET / NFSD_CMD_LISTENER_GET).
  *
- * These cover the request validation that nfsd_nl_validate_listeners() does
- * before nfsd_mutex is taken: bad or absent transport name, missing address,
- * truncated or unsupported sockaddr, oversized list. None of them reach
- * nfsd_create_serv(), so nothing here creates a serv or talks to rpcbind.
+ * Three groups:
+ *   validation  - malformed/abusive LISTENER_SET requests are rejected by
+ *                 nfsd_nl_validate_listeners(), before nfsd_mutex is taken.
+ *   functional  - create/add/remove listeners and verify LISTENER_GET
+ *                 reflects the set (round-trip of transport + addr:port).
+ *   semantics   - once threads are running (THREADS_SET) a listener change
+ *                 is refused with -EBUSY.
  *
  * Each test runs in its own private net + mount namespace (unshare in
  * FIXTURE_SETUP). /run is masked there: a pathname AF_LOCAL connect is not
  * scoped by the network namespace, since unix_find_bsd() resolves by inode
  * and takes no struct net, so the kernel's rpcbind client would otherwise be
- * able to reach the rpcbind running on the host.
+ * able to reach the rpcbind running on the host. Anything that creates a
+ * serv is served by the per-netns rpcbind stub below instead.
  */
 #define _GNU_SOURCE
 #include <errno.h>
+#include <poll.h>
 #include <sched.h>
+#include <signal.h>
+#include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include <sys/mman.h>
 #include <sys/mount.h>
+#include <sys/prctl.h>
 #include <sys/socket.h>
 #include <sys/ioctl.h>
 #include <sys/stat.h>
 #include <sys/time.h>
+#include <sys/un.h>
+#include <sys/wait.h>
 #include <net/if.h>
 #include <netinet/in.h>
 #include <linux/netlink.h>
@@ -36,8 +47,10 @@
 
 /* NFSD generic-netlink constants (from linux/nfsd_netlink.h). */
 #define NFSD_FAMILY_NAME		"nfsd"
+#define NFSD_CMD_THREADS_SET		2
 #define NFSD_CMD_LISTENER_SET		6
 #define NFSD_CMD_LISTENER_GET		7
+#define NFSD_A_SERVER_THREADS		1
 #define NFSD_A_SERVER_SOCK_ADDR		1	/* per-listener nest */
 #define NFSD_A_SOCK_ADDR		1	/* inside the nest */
 #define NFSD_A_SOCK_TRANSPORT_NAME	2	/* inside the nest */
@@ -327,10 +340,293 @@ static int listener_get(struct listener_ent *out, int max)
 	return parse_listener_get(rbuf, n, out, max);
 }
 
+/*
+ * Every listener these tests create comes from put_listener_af(), so the
+ * address is always loopback. Match on it too: without that, a reply that
+ * gave the right transport and port on the wrong address (0.0.0.0, say)
+ * would pass.
+ */
+static struct listener_ent *find_listener(struct listener_ent *e, int n,
+					  const char *xprt, int family,
+					  uint16_t port)
+{
+	int i;
+
+	for (i = 0; i < n; i++) {
+		if (e[i].family != family || e[i].port != port ||
+		    strcmp(e[i].xprt, xprt))
+			continue;
+		if (family == AF_INET6) {
+			if (memcmp(&e[i].a6, &in6addr_loopback, sizeof(e[i].a6)))
+				continue;
+		} else if (e[i].a4.s_addr != htonl(INADDR_LOOPBACK)) {
+			continue;
+		}
+		return &e[i];
+	}
+	return NULL;
+}
+
+/* Start (@n > 0) or stop (@n == 0) nfsd threads in this netns. */
+static int threads_set(int n)
+{
+	char attrs[64];
+	uint32_t v = n;
+	int off = put_attr(attrs, 0, NFSD_A_SERVER_THREADS, &v, sizeof(v));
+
+	return genl_request(NFSD_CMD_THREADS_SET, attrs, off);
+}
+
+/* ------------------- per-netns local rpcbind stub ------------------- */
+
+/*
+ * Creating a listener registers with rpcbind: svc_xprt_create_from_sa()
+ * passes flags of 0, so pmap_register is true in svc_setup_socket(), and
+ * nfsd_version3 is registerable by default and does not set vs_rpcb_optnl,
+ * so a registration failure aborts listener creation. The abstract AF_LOCAL
+ * name the kernel tries first is per-netns (unix_find_abstract() takes a
+ * struct net), so answer it here and stay out of the host's rpcbind.
+ *
+ * Arguments are never decoded. The NULL procedure gets an empty success and
+ * SET/UNSET get TRUE, for both RPCBVERS_2 and RPCBVERS_4. v4 has to be
+ * answered because __svc_rpcb_register6() turns a v4 refusal into
+ * -EAFNOSUPPORT, which would fail every IPv6 listener.
+ *
+ * In RPCB_STUB_REFUSE mode SET is answered FALSE instead, which
+ * rpcb_register_call() reports as -EACCES. UNSET is left alone: only
+ * svc_unregister() issues it, and it discards the result.
+ *
+ * The stub also keeps counters in a page shared with the test, so a test can
+ * assert that the kernel never talked to rpcbind at all, or that it dropped
+ * the local rpcbind client and had to reconnect.
+ */
+#define RPCB_PROGRAM		100000
+#define RPCB_PROC_NULL		0
+#define RPCB_PROC_SET		1
+#define RPCB_PROC_UNSET		2
+#define RPCB_ABSTRACT_NAME	"/run/rpcbind.sock"
+#define RPCB_STUB_MAXCONN	4
+
+enum { RPCB_STUB_ACCEPT, RPCB_STUB_REFUSE };
+
+struct rpcb_stub_stats {
+	unsigned int conns;		/* connections accepted */
+	unsigned int calls;		/* calls answered */
+};
+
+static volatile struct rpcb_stub_stats *rpcb_stats;	/* MAP_SHARED */
+
+static int rpcb_stats_alloc(void)
+{
+	void *p = mmap(NULL, sizeof(*rpcb_stats), PROT_READ | PROT_WRITE,
+		       MAP_SHARED | MAP_ANONYMOUS, -1, 0);
+
+	if (p == MAP_FAILED)
+		return -1;
+	rpcb_stats = p;
+	return 0;
+}
+
+/*
+ * The stub bumps these before it replies and the kernel waits for that reply,
+ * so whatever a netlink request provoked is visible once it returns.
+ */
+static int rpcb_calls(void)
+{
+	return rpcb_stats ? (int)rpcb_stats->calls : 0;
+}
+
+static int rpcb_conns(void)
+{
+	return rpcb_stats ? (int)rpcb_stats->conns : 0;
+}
+
+static int rpcb_stub_listen(void)
+{
+	struct sockaddr_un sun = { .sun_family = AF_UNIX };
+	size_t nlen = strlen(RPCB_ABSTRACT_NAME);
+	socklen_t alen;
+	int fd;
+
+	/* Abstract names are length-delimited, so the length must match. */
+	memcpy(sun.sun_path + 1, RPCB_ABSTRACT_NAME, nlen);
+	alen = offsetof(struct sockaddr_un, sun_path) + 1 + nlen;
+
+	fd = socket(AF_UNIX, SOCK_STREAM, 0);
+	if (fd < 0)
+		return -1;
+	if (bind(fd, (struct sockaddr *)&sun, alen) < 0 ||
+	    listen(fd, RPCB_STUB_MAXCONN) < 0) {
+		close(fd);
+		return -1;
+	}
+	return fd;
+}
+
+static int rpcb_stub_read(int fd, void *buf, size_t len)
+{
+	size_t done = 0;
+
+	while (done < len) {
+		ssize_t n = read(fd, (char *)buf + done, len - done);
+
+		if (n <= 0)
+			return -1;
+		done += n;
+	}
+	return 0;
+}
+
+/* Handle one record-marked RPC call. Returns -1 when the peer is done. */
+static int rpcb_stub_call(int fd, int mode)
+{
+	uint32_t mark, call[6], rep[7];
+	unsigned int len, nrep = 6;
+	size_t replen;
+
+	if (rpcb_stub_read(fd, &mark, sizeof(mark)))
+		return -1;
+	len = ntohl(mark) & 0x7fffffff;
+	if (len < sizeof(call) || len > 4096)
+		return -1;
+	if (rpcb_stub_read(fd, call, sizeof(call)))
+		return -1;
+
+	/* xid, msg_type, rpcvers, prog, vers, proc; the rest is discarded */
+	for (len -= sizeof(call); len; ) {
+		char sink[256];
+		unsigned int n = len > sizeof(sink) ? sizeof(sink) : len;
+
+		if (rpcb_stub_read(fd, sink, n))
+			return -1;
+		len -= n;
+	}
+
+	if (rpcb_stats)
+		rpcb_stats->calls++;
+
+	rep[0] = call[0];		/* xid */
+	rep[1] = htonl(1);		/* REPLY */
+	rep[2] = htonl(0);		/* MSG_ACCEPTED */
+	rep[3] = htonl(0);		/* verifier flavor AUTH_NULL */
+	rep[4] = htonl(0);		/* verifier length */
+	rep[5] = htonl(0);		/* SUCCESS */
+
+	if (ntohl(call[3]) != RPCB_PROGRAM) {
+		rep[5] = htonl(1);	/* PROG_UNAVAIL */
+	} else {
+		switch (ntohl(call[5])) {
+		case RPCB_PROC_NULL:
+			break;
+		case RPCB_PROC_SET:
+			rep[6] = htonl(mode == RPCB_STUB_REFUSE ? 0 : 1);
+			nrep = 7;
+			break;
+		case RPCB_PROC_UNSET:
+			rep[6] = htonl(1);	/* TRUE */
+			nrep = 7;
+			break;
+		default:
+			rep[5] = htonl(3);	/* PROC_UNAVAIL */
+		}
+	}
+
+	replen = nrep * sizeof(rep[0]);
+	mark = htonl(0x80000000 | replen);
+	if (write(fd, &mark, sizeof(mark)) != (ssize_t)sizeof(mark) ||
+	    write(fd, rep, replen) != (ssize_t)replen)
+		return -1;
+	return 0;
+}
+
+static void rpcb_stub_serve(int lfd, int mode)
+{
+	struct pollfd pfd[1 + RPCB_STUB_MAXCONN];
+	nfds_t n = 1, i;
+
+	pfd[0].fd = lfd;
+
+	for (;;) {
+		/* stop polling the listener when full, or poll() spins */
+		pfd[0].events = n < 1 + RPCB_STUB_MAXCONN ? POLLIN : 0;
+
+		if (poll(pfd, n, -1) < 0)
+			return;
+
+		if (pfd[0].revents & POLLIN) {
+			int c = accept(lfd, NULL, NULL);
+
+			if (c >= 0) {
+				pfd[n].fd = c;
+				pfd[n].events = POLLIN;
+				/*
+				 * poll() ran with the old n, so it did not
+				 * write this revents. The loop below reads it.
+				 */
+				pfd[n].revents = 0;
+				n++;
+				if (rpcb_stats)
+					rpcb_stats->conns++;
+			}
+		}
+
+		for (i = 1; i < n; i++) {
+			if (!(pfd[i].revents & (POLLIN | POLLHUP | POLLERR)))
+				continue;
+			if (rpcb_stub_call(pfd[i].fd, mode)) {
+				close(pfd[i].fd);
+				pfd[i] = pfd[--n];
+			}
+		}
+	}
+}
+
+/* Returns the stub's pid, or -1. The socket is listening before we fork. */
+static pid_t rpcb_stub_start(int mode)
+{
+	int lfd = rpcb_stub_listen();
+	pid_t pid;
+
+	if (lfd < 0)
+		return -1;
+
+	pid = fork();
+	if (pid < 0) {
+		close(lfd);
+		return -1;
+	}
+	if (pid == 0) {
+		signal(SIGPIPE, SIG_IGN);
+		prctl(PR_SET_PDEATHSIG, SIGKILL);
+		if (getppid() == 1)		/* raced with parent exit */
+			_exit(0);
+		rpcb_stub_serve(lfd, mode);
+		_exit(0);
+	}
+
+	close(lfd);
+	return pid;
+}
+
+/*
+ * Swap the stub for one in @mode. Safe before the first request: no serv
+ * exists yet, so the kernel has not connected and the abstract name is free
+ * again once the old stub has been reaped.
+ */
+static int rpcb_stub_restart(pid_t *pid, int mode)
+{
+	if (*pid > 0) {
+		kill(*pid, SIGKILL);
+		waitpid(*pid, NULL, 0);
+	}
+	*pid = rpcb_stub_start(mode);
+	return *pid > 0 ? 0 : -1;
+}
+
 /* --------------------------- fixture --------------------------- */
 
 FIXTURE(nfsd_listener) {
-	int placeholder;
+	pid_t rpcbd;
 };
 
 FIXTURE_SETUP(nfsd_listener)
@@ -369,14 +665,35 @@ FIXTURE_SETUP(nfsd_listener)
 	nfsd_family = genl_resolve_nfsd();
 	if (nfsd_family < 0)
 		SKIP(return, "nfsd genl family not found (modprobe nfsd?)");
+
+	if (rpcb_stats_alloc() < 0)
+		SKIP(return, "mmap(rpcbind stub counters): %s", strerror(errno));
+
+	self->rpcbd = rpcb_stub_start(RPCB_STUB_ACCEPT);
+	if (self->rpcbd < 0)
+		SKIP(return, "cannot start the rpcbind stub: %s",
+		     strerror(errno));
 }
 
 FIXTURE_TEARDOWN(nfsd_listener)
 {
+	if (self->rpcbd > 0) {
+		kill(self->rpcbd, SIGKILL);
+		waitpid(self->rpcbd, NULL, 0);
+	}
+	if (rpcb_stats) {
+		munmap((void *)rpcb_stats, sizeof(*rpcb_stats));
+		rpcb_stats = NULL;
+	}
 }
 
 /* ===================== validation / negative ===================== */
 
+TEST_F(nfsd_listener, val_empty_list_ok)
+{
+	EXPECT_EQ(0, listener_set(NULL, 0));
+}
+
 TEST_F(nfsd_listener, val_too_many)
 {
 	static char attrs[1 << 20];
@@ -411,13 +728,21 @@ TEST_F(nfsd_listener, val_missing_transport)
  * A name matching no transport class must be refused before nfsd_mutex is
  * taken, so it never reaches svc_xprt_create_from_sa() and its
  * request_module("svc%s", name) upcall.
+ *
+ * The errno cannot show that -- svc_xprt_create_from_sa() returns
+ * -EPROTONOSUPPORT for an unknown name too. The rpcbind traffic can:
+ * getting that far means nfsd_create_serv() ran, and svc_bind() pings
+ * rpcbind at client creation and then sweeps stale entries with
+ * svc_unregister(). A silent stub is the proof nothing was created.
  */
 TEST_F(nfsd_listener, val_bad_transport)
 {
 	char attrs[64];
 	int off = put_listener(attrs, 0, "bogus_xprt", TEST_PORT);
 
+	ASSERT_EQ(0, rpcb_calls());
 	EXPECT_EQ(-EPROTONOSUPPORT, listener_set(attrs, off));
+	EXPECT_EQ(0, rpcb_calls());
 }
 
 TEST_F(nfsd_listener, val_addr_too_short)
@@ -469,14 +794,49 @@ TEST_F(nfsd_listener, val_second_entry_bad)
 	struct sockaddr_storage ss = { .ss_family = AF_UNIX };
 	struct raw_listener bad = { .xprt = "tcp", .emit_addr = 1, .addr = &ss,
 				    .addr_len = sizeof(struct sockaddr_in) };
+	struct listener_ent got[MAX_LISTENERS];
 	char attrs[128];
 	int off = put_listener(attrs, 0, "tcp", TEST_PORT);
 
 	off = put_raw_listener(attrs, off, &bad);
 	/* The whole request is rejected during validation; nothing applied. */
 	EXPECT_EQ(-EAFNOSUPPORT, listener_set(attrs, off));
+	/*
+	 * Again the errno alone does not say so: svc_xprt_create_from_sa()
+	 * also returns -EAFNOSUPPORT, and the doit keeps the listeners it did
+	 * manage to create, so the well-formed tcp entry ahead of the bad one
+	 * would still be up.
+	 */
+	EXPECT_EQ(0, listener_get(got, MAX_LISTENERS));
 }
 
+/*
+ * A rejected request must leave the listeners that are already up alone.
+ * The errno alone does not show that: svc_xprt_create_from_sa() returns
+ * -EPROTONOSUPPORT for an unknown name too. What differs is how far the
+ * request gets -- without the check in nfsd_nl_validate_listeners(),
+ * nfsd_nl_listener_set_doit() has already moved the unmatched tcp listener
+ * off sv_permsocks and run svc_xprt_destroy_all() on it by the time the
+ * name fails.
+ */
+TEST_F(nfsd_listener, val_reject_keeps_listeners)
+{
+	struct listener_ent got[MAX_LISTENERS];
+	char good[64], bad[64];
+	int og = put_listener(good, 0, "tcp", TEST_PORT);
+	int ob = put_listener(bad, 0, "bogus_xprt", TEST_PORT);
+
+	ASSERT_EQ(0, listener_set(good, og));
+	ASSERT_EQ(1, listener_get(got, MAX_LISTENERS));
+
+	EXPECT_EQ(-EPROTONOSUPPORT, listener_set(bad, ob));
+
+	ASSERT_EQ(1, listener_get(got, MAX_LISTENERS));
+	EXPECT_NE(NULL, find_listener(got, 1, "tcp", AF_INET, TEST_PORT));
+}
+
+/* ===================== functional / round-trip ===================== */
+
 /* LISTENER_GET with no serv in this netns returns an empty list. */
 TEST_F(nfsd_listener, func_get_empty)
 {
@@ -485,4 +845,186 @@ TEST_F(nfsd_listener, func_get_empty)
 	EXPECT_EQ(0, listener_get(got, MAX_LISTENERS));
 }
 
+TEST_F(nfsd_listener, func_create_tcp)
+{
+	struct listener_ent got[MAX_LISTENERS];
+	char attrs[64];
+	int off = put_listener(attrs, 0, "tcp", TEST_PORT);
+
+	ASSERT_EQ(0, listener_set(attrs, off));
+	ASSERT_EQ(1, listener_get(got, MAX_LISTENERS));
+	EXPECT_NE(NULL, find_listener(got, 1, "tcp", AF_INET, TEST_PORT));
+}
+
+TEST_F(nfsd_listener, func_create_udp)
+{
+	struct listener_ent got[MAX_LISTENERS];
+	char attrs[64];
+	int off = put_listener(attrs, 0, "udp", TEST_PORT);
+
+	ASSERT_EQ(0, listener_set(attrs, off));
+	ASSERT_EQ(1, listener_get(got, MAX_LISTENERS));
+	EXPECT_NE(NULL, find_listener(got, 1, "udp", AF_INET, TEST_PORT));
+}
+
+TEST_F(nfsd_listener, func_create_multi)
+{
+	struct listener_ent got[MAX_LISTENERS];
+	char attrs[128];
+	int off = put_listener(attrs, 0, "tcp", TEST_PORT);
+
+	off = put_listener(attrs, off, "udp", TEST_PORT);
+	ASSERT_EQ(0, listener_set(attrs, off));
+	ASSERT_EQ(2, listener_get(got, MAX_LISTENERS));
+	EXPECT_NE(NULL, find_listener(got, 2, "tcp", AF_INET, TEST_PORT));
+	EXPECT_NE(NULL, find_listener(got, 2, "udp", AF_INET, TEST_PORT));
+}
+
+TEST_F(nfsd_listener, func_idempotent)
+{
+	struct listener_ent got[MAX_LISTENERS];
+	char attrs[64];
+	int off = put_listener(attrs, 0, "tcp", TEST_PORT);
+
+	ASSERT_EQ(0, listener_set(attrs, off));
+	EXPECT_EQ(0, listener_set(attrs, off));		/* re-set same list */
+	ASSERT_EQ(1, listener_get(got, MAX_LISTENERS));
+	EXPECT_NE(NULL, find_listener(got, 1, "tcp", AF_INET, TEST_PORT));
+}
+
+TEST_F(nfsd_listener, func_add)
+{
+	struct listener_ent got[MAX_LISTENERS];
+	char one[64], two[128];
+	int o1 = put_listener(one, 0, "tcp", TEST_PORT);
+	int o2 = put_listener(two, 0, "tcp", TEST_PORT);
+
+	o2 = put_listener(two, o2, "udp", TEST_PORT);
+	ASSERT_EQ(0, listener_set(one, o1));
+	ASSERT_EQ(0, listener_set(two, o2));		/* add udp, keep tcp */
+	ASSERT_EQ(2, listener_get(got, MAX_LISTENERS));
+	EXPECT_NE(NULL, find_listener(got, 2, "tcp", AF_INET, TEST_PORT));
+	EXPECT_NE(NULL, find_listener(got, 2, "udp", AF_INET, TEST_PORT));
+}
+
+TEST_F(nfsd_listener, func_remove_subset)
+{
+	struct listener_ent got[MAX_LISTENERS];
+	char both[128], one[64];
+	int ob = put_listener(both, 0, "tcp", TEST_PORT);
+	int oo = put_listener(one, 0, "tcp", TEST_PORT);
+
+	ob = put_listener(both, ob, "udp", TEST_PORT);
+	ASSERT_EQ(0, listener_set(both, ob));
+	ASSERT_EQ(0, listener_set(one, oo));		/* drop udp */
+	ASSERT_EQ(1, listener_get(got, MAX_LISTENERS));
+	EXPECT_NE(NULL, find_listener(got, 1, "tcp", AF_INET, TEST_PORT));
+}
+
+/*
+ * LISTENER_GET cannot tell a destroyed serv from a live one with no
+ * permsocks: nfsd_nl_listener_get_doit() replies empty either way. The
+ * rpcbind client can. nfsd_destroy_serv() is the only path that reaches
+ * svc_xprt_destroy_all(..., unregister=true) -> svc_rpcb_cleanup() ->
+ * rpcb_put_local(), which drops the last user and shuts the local client
+ * down; the next serv then has to connect again. Leaving the serv in place
+ * would keep the first connection and the stub would see just the one.
+ */
+TEST_F(nfsd_listener, func_empty_destroys)
+{
+	struct listener_ent got[MAX_LISTENERS];
+	char attrs[64];
+	int off = put_listener(attrs, 0, "tcp", TEST_PORT);
+	int conns;
+
+	ASSERT_EQ(0, listener_set(attrs, off));
+	conns = rpcb_conns();
+	ASSERT_GT(conns, 0);
+
+	EXPECT_EQ(0, listener_set(NULL, 0));		/* empty -> destroy serv */
+	EXPECT_EQ(0, listener_get(got, MAX_LISTENERS));
+
+	ASSERT_EQ(0, listener_set(attrs, off));
+	EXPECT_GT(rpcb_conns(), conns);
+}
+
+TEST_F(nfsd_listener, func_ipv6)
+{
+	struct listener_ent got[MAX_LISTENERS];
+	char attrs[64];
+	int off, s;
+
+	s = socket(AF_INET6, SOCK_STREAM, 0);
+	if (s < 0)
+		SKIP(return, "IPv6 unavailable: %s", strerror(errno));
+	close(s);
+
+	off = put_listener_af(attrs, 0, "tcp", AF_INET6, TEST_PORT);
+	ASSERT_EQ(0, listener_set(attrs, off));
+	ASSERT_EQ(1, listener_get(got, MAX_LISTENERS));
+	EXPECT_NE(NULL, find_listener(got, 1, "tcp", AF_INET6, TEST_PORT));
+}
+
+/* ===================== rpcbind registration ===================== */
+
+/*
+ * A rpcbind that refuses the registration must fail listener creation,
+ * whatever CONFIG_NFS_LOCALIO is set to.
+ *
+ * The error has to survive svc_register()'s walk over sv_programs to get
+ * here. With CONFIG_NFS_LOCALIO=y the trailing nfslocalio program has only
+ * a NULL and a vs_hidden version, and svc_generic_rpcbind_set() reports 0
+ * for both, so an svc_register() that keeps the last result rather than the
+ * first hands back success and the listener comes up regardless.
+ */
+TEST_F(nfsd_listener, sem_register_refused)
+{
+	struct listener_ent got[MAX_LISTENERS];
+	char attrs[64];
+	int off = put_listener(attrs, 0, "tcp", TEST_PORT);
+
+	ASSERT_EQ(0, rpcb_stub_restart(&self->rpcbd, RPCB_STUB_REFUSE));
+
+	EXPECT_EQ(-EACCES, listener_set(attrs, off));
+	EXPECT_EQ(0, listener_get(got, MAX_LISTENERS));
+}
+
+/* ===================== threads / -EBUSY semantics ===================== */
+
+TEST_F(nfsd_listener, sem_busy_on_change)
+{
+	struct listener_ent got[MAX_LISTENERS];
+	char one[64], two[128];
+	int o1 = put_listener(one, 0, "tcp", TEST_PORT);
+	int o2 = put_listener(two, 0, "tcp", TEST_PORT);
+
+	o2 = put_listener(two, o2, "udp", TEST_PORT);
+	ASSERT_EQ(0, listener_set(one, o1));
+	ASSERT_EQ(0, threads_set(1));			/* threads now running */
+	EXPECT_EQ(-EBUSY, listener_set(two, o2));	/* add refused */
+
+	/* refused means refused: the udp listener must not have been added */
+	EXPECT_EQ(1, listener_get(got, MAX_LISTENERS));
+	EXPECT_NE(NULL, find_listener(got, 1, "tcp", AF_INET, TEST_PORT));
+
+	threads_set(0);					/* stop before netns exit */
+}
+
+TEST_F(nfsd_listener, sem_busy_on_remove)
+{
+	struct listener_ent got[MAX_LISTENERS];
+	char one[64];
+	int o1 = put_listener(one, 0, "tcp", TEST_PORT);
+
+	ASSERT_EQ(0, listener_set(one, o1));
+	ASSERT_EQ(0, threads_set(1));
+	EXPECT_EQ(-EBUSY, listener_set(NULL, 0));	/* remove refused */
+
+	/* the doit moves the permsocks to a temp list before it can fail */
+	EXPECT_EQ(1, listener_get(got, MAX_LISTENERS));
+	EXPECT_NE(NULL, find_listener(got, 1, "tcp", AF_INET, TEST_PORT));
+
+	threads_set(0);
+}
+
 TEST_HARNESS_MAIN

-- 
2.55.0

Re: [PATCH v2 8/8] selftests/nfsd: add a per-netns rpcbind stub and the listener round-trips

[Chuck Lever]

On Tue, Aug 11, 2026, at 8:03 AM, Jeff Layton wrote:
> Creating a listener registers with rpcbind: svc_xprt_create_from_sa() passes
> flags of 0, so pmap_register is true in svc_setup_socket(), and
> nfsd_version3 is enabled by default and does not set vs_rpcb_optnl, so a
> registration failure aborts listener creation. A fresh netns has no rpcbind,
> and reaching the host's is not an option -- svc_rpcb_setup() opens by
> calling svc_unregister(), which would clear the host's nfsd entries.

>  /* --------------------------- fixture --------------------------- */
> 
>  FIXTURE(nfsd_listener) {
> -	int placeholder;
> +	pid_t rpcbd;
>  };
> 
>  FIXTURE_SETUP(nfsd_listener)
> @@ -369,14 +665,35 @@ FIXTURE_SETUP(nfsd_listener)
>  	nfsd_family = genl_resolve_nfsd();
>  	if (nfsd_family < 0)
>  		SKIP(return, "nfsd genl family not found (modprobe nfsd?)");
> +
> +	if (rpcb_stats_alloc() < 0)
> +		SKIP(return, "mmap(rpcbind stub counters): %s", strerror(errno));
> +
> +	self->rpcbd = rpcb_stub_start(RPCB_STUB_ACCEPT);
> +	if (self->rpcbd < 0)
> +		SKIP(return, "cannot start the rpcbind stub: %s",
> +		     strerror(errno));
>  }
> 
>  FIXTURE_TEARDOWN(nfsd_listener)
>  {
> +	if (self->rpcbd > 0) {
> +		kill(self->rpcbd, SIGKILL);
> +		waitpid(self->rpcbd, NULL, 0);
> +	}
> +	if (rpcb_stats) {
> +		munmap((void *)rpcb_stats, sizeof(*rpcb_stats));
> +		rpcb_stats = NULL;
> +	}
>  }

The fixture appears to leak the network namespace for the tests that
finish with a listener still up. Would something along these lines in
FIXTURE_TEARDOWN() cover it?

	/* A live listener pins the netns; drop any serv the test made. */
	if (listener_set(NULL, 0) == -EBUSY)
		threads_set(0);


-- 
Chuck Lever