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

[Jeff Layton]

On Sun, 2026-06-07 at 07:06 -0700, Weiming Shi wrote:
> 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@xxxxxxx>
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: Weiming Shi <bestswngs@xxxxxxxxx>
> ---
>  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) {

Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>