[PATCH] SUNRPC: check rpc_sockaddr2uaddr() return value in rpcb_register_inet4/6

[Weiming Shi <bestswngs@gmail.com>]

rpcb_register_inet4() and rpcb_register_inet6() store the result of
rpc_sockaddr2uaddr() into map->r_addr without checking it for NULL.
rpc_sockaddr2uaddr() returns NULL when its final kstrdup() fails, and
the unchecked NULL is then carried into the synchronous RPCBPROC_SET
encode path: rpcb_register_call() -> rpc_call_sync() ->
rpcb_enc_getaddr() -> encode_rpcb_string(), whose first statement is
strlen(string), dereferencing NULL and oopsing the kernel.

The crash reproduces under failslab on v6.12; with KASAN the NULL
dereference surfaces as a fault on the shadow of address zero:

 Oops: general protection fault, probably for non-canonical address
       0xdffffc0000000000 [#1] PREEMPT SMP KASAN
 RIP: 0010:strlen (lib/string.c:409)
 Call Trace:
  encode_rpcb_string (net/sunrpc/rpcb_clnt.c:890)
  rpcb_enc_getaddr (net/sunrpc/rpcb_clnt.c:910)
  rpcauth_wrap_req_encode (net/sunrpc/auth.c:745)
  call_encode (net/sunrpc/clnt.c:1966)
  __rpc_execute (net/sunrpc/sched.c:952)
  rpc_run_task (net/sunrpc/clnt.c:1243)
  rpc_call_sync (net/sunrpc/clnt.c:1272)
  rpcb_v4_register (net/sunrpc/rpcb_clnt.c:500)
  svc_generic_rpcbind_set
  nfsd_rpcbind_set
  svc_register
  svc_setup_socket
  svc_addsock
  write_ports
  nfsctl_transaction_write
  vfs_write

The crash is reachable when an in-kernel RPC service (nfsd, lockd,
nfs-callback) registers with the local rpcbind under enough memory
pressure for the small GFP_KERNEL kstrdup() in rpc_sockaddr2uaddr() to
fail. The asynchronous getport path already handles this exact failure
mode by returning -ENOMEM; only the two register helpers omit the check.

Mirror that handling: bail out with -ENOMEM when rpc_sockaddr2uaddr()
returns NULL, before the address is fed into the encoder.

Fixes: d77385f23830 ("SUNRPC: Fix rpc_sockaddr2uaddr")
Reported-by: Xiang Mei <xmei5@asu.edu>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
---
 net/sunrpc/rpcb_clnt.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/sunrpc/rpcb_clnt.c b/net/sunrpc/rpcb_clnt.c
index 6aa372188c86..4c0b7fefee4e 100644
--- a/net/sunrpc/rpcb_clnt.c
+++ b/net/sunrpc/rpcb_clnt.c
@@ -490,6 +490,8 @@ static int rpcb_register_inet4(struct sunrpc_net *sn,
 	int result;
 
 	map->r_addr = rpc_sockaddr2uaddr(sap, GFP_KERNEL);
+	if (!map->r_addr)
+		return -ENOMEM;
 
 	msg->rpc_proc = &rpcb_procedures4[RPCBPROC_UNSET];
 	if (port != 0) {
@@ -516,6 +518,8 @@ static int rpcb_register_inet6(struct sunrpc_net *sn,
 	int result;
 
 	map->r_addr = rpc_sockaddr2uaddr(sap, GFP_KERNEL);
+	if (!map->r_addr)
+		return -ENOMEM;
 
 	msg->rpc_proc = &rpcb_procedures4[RPCBPROC_UNSET];
 	if (port != 0) {
-- 
2.43.0