sunrpc: handle SVC_GARBAGE during svc auth processing as auth error

jira VULN-71608
cve CVE-2025-38089
commit-author Jeff Layton <jlayton@kernel.org>
commit 94d10a4
upstream-diff The following commits cause merge conflicts since they are
    not present in the fips-9-compliant/5.14.0-284.30.1 :-
    6d037b1 ("SUNRPC: Remove the rpc_stat variable in svc_process_common()")
    ab42f4d ("sunrpc: don't change ->sv_stats if it doesn't exist")
    649a692 ("SUNRPC: Convert RPC Reply header encoding to use xdr_stream")

tianshuo han reported a remotely-triggerable crash if the client sends a
kernel RPC server a specially crafted packet. If decoding the RPC reply
fails in such a way that SVC_GARBAGE is returned without setting the
rq_accept_statp pointer, then that pointer can be dereferenced and a
value stored there.

If it's the first time the thread has processed an RPC, then that
pointer will be set to NULL and the kernel will crash. In other cases,
it could create a memory scribble.

The server sunrpc code treats a SVC_GARBAGE return from svc_authenticate
or pg_authenticate as if it should send a GARBAGE_ARGS reply. RFC 5531
says that if authentication fails that the RPC should be rejected
instead with a status of AUTH_ERR.

Handle a SVC_GARBAGE return as an AUTH_ERROR, with a reason of
AUTH_BADCRED instead of returning GARBAGE_ARGS in that case. This
sidesteps the whole problem of touching the rpc_accept_statp pointer in
this situation and avoids the crash.

	Cc: stable@kernel.org
Fixes: 29cd292 ("SUNRPC: Fix encoding of accepted but unsuccessful RPC replies")
	Reported-by: tianshuo han <hantianshuo233@gmail.com>
	Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
	Signed-off-by: Jeff Layton <jlayton@kernel.org>
	Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
(cherry picked from commit 94d10a4)
	Signed-off-by: Shreeya Patel <spatel@ciq.com>

Author: shreeya-patel98

net/sunrpc/svc.c

@@ -1287,7 +1287,8 @@ svc_process_common(struct svc_rqst *rqstp, struct kvec *argv, struct kvec *resv)
 	case SVC_OK:
 		break;
 	case SVC_GARBAGE:
-		goto err_garbage;
+		rqstp->rq_auth_stat = rpc_autherr_badcred;
+		goto err_bad_auth;
 	case SVC_SYSERR:
 		rpc_stat = rpc_system_err;
 		goto err_bad;
@@ -1416,10 +1417,6 @@ svc_process_common(struct svc_rqst *rqstp, struct kvec *argv, struct kvec *resv)
 	svc_putnl(resv, RPC_PROC_UNAVAIL);
 	goto sendit;
 
-err_garbage:
-	svc_printk(rqstp, "failed to decode args\n");
-
-	rpc_stat = rpc_garbage_args;
 err_bad:
 	serv->sv_stats->rpcbadfmt++;
 	svc_putnl(resv, ntohl(rpc_stat));