Re: [PATCH net 1/2] net/rds: do not fail init when CONFIG_SYSCTL=n

With CONFIG_SYSCTL=n, register_net_sysctl() and register_net_sysctl_sz()
are inline stubs that return NULL.  rds_sysctl_init(),
rds_ib_sysctl_init() and rds_tcp_init_net() all treat that NULL as
-ENOMEM, so RDS refuses to initialize at all even though every tunable
has a sane compiled-in default.

When RDS is built in, that is worse than a missing feature: the failed
rds_init() destroys rds_wq, but the rds_rdma initcall still runs, and
when rds_ib_sysctl_init() fails the same way, the error path in
rds_ib_init() flushes the already freed workqueue:

  BUG: KASAN: slab-use-after-free in touch_wq_lockdep_map
  ...
   __flush_workqueue
   rds_ib_init
   rds_rdma_init
  ...
  Allocated by task 1:
   alloc_workqueue_noprof
   rds_threads_init
   rds_init
  ...
  Freed by task 0:
   kfree
   rcu_do_batch

Only treat the NULL return as a failure when sysctl support is actually
compiled in.  The exit paths need no change: unregister_net_sysctl_table()
is an empty stub with CONFIG_SYSCTL=n and already tolerates a NULL header
otherwise.

The underlying problem of built-in transports initializing after
rds_init() has failed is independent of sysctl and is addressed
separately.

Reported-by: kernel test robot <redacted>
Closes: https://lore.kernel.org/oe-lkp/202610190310.9737b2e3-lkp@intel.com (local)
Fixes: 3e5048495c85 ("RDS: sysctls")
Fixes: e6babe4cc4ce ("RDS/IB: Stats and sysctls")
Fixes: c6a58ffed536 ("RDS: TCP: Add sysctl tunables for sndbuf/rcvbuf on rds-tcp socket")
Suggested-by: Joel Granados <joel.granados@kernel.org>
Assisted-by: LLM
Signed-off-by: Allison Henderson <achender@kernel.org>
---
 net/rds/ib_sysctl.c | 2 +-
 net/rds/sysctl.c    | 2 +-
 net/rds/tcp.c       | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/rds/ib_sysctl.c b/net/rds/ib_sysctl.c
index 2af678e71e3c..bc97a3eecad6 100644
--- a/net/rds/ib_sysctl.c
+++ b/net/rds/ib_sysctl.c

@@ -114,7 +114,7 @@ void rds_ib_sysctl_exit(void)
 int rds_ib_sysctl_init(void)
 {
 	rds_ib_sysctl_hdr = register_net_sysctl(&init_net, "net/rds/ib", rds_ib_sysctl_table);
-	if (!rds_ib_sysctl_hdr)
+	if (!rds_ib_sysctl_hdr && IS_ENABLED(CONFIG_SYSCTL))
 		return -ENOMEM;
 	return 0;
 }

diff --git a/net/rds/sysctl.c b/net/rds/sysctl.c
index 025f518a4349..968d6279bbd3 100644
--- a/net/rds/sysctl.c
+++ b/net/rds/sysctl.c

@@ -103,7 +103,7 @@ int rds_sysctl_init(void)
 
 	rds_sysctl_reg_table =
 		register_net_sysctl(&init_net, "net/rds", rds_sysctl_rds_table);
-	if (!rds_sysctl_reg_table)
+	if (!rds_sysctl_reg_table && IS_ENABLED(CONFIG_SYSCTL))
 		return -ENOMEM;
 	return 0;
 }

diff --git a/net/rds/tcp.c b/net/rds/tcp.c
index 774a71f88d37..34815b4f658b 100644
--- a/net/rds/tcp.c
+++ b/net/rds/tcp.c

@@ -637,7 +637,7 @@ static __net_init int rds_tcp_init_net(struct net *net)
 	tbl[RDS_TCP_RCVBUF].data = &rtn->rcvbuf_size;
 	rtn->rds_tcp_sysctl = register_net_sysctl_sz(net, "net/rds/tcp", tbl,
 						     ARRAY_SIZE(rds_tcp_sysctl_table));
-	if (!rtn->rds_tcp_sysctl) {
+	if (!rtn->rds_tcp_sysctl && IS_ENABLED(CONFIG_SYSCTL)) {
 		pr_warn("could not register sysctl\n");
 		err = -ENOMEM;
 		goto fail;

-- 
2.50.1