[PATCH] sunrpc: handle SVC_GARBAGE during svc auth processing as auth error

[PATCH] sunrpc: handle SVC_GARBAGE during svc auth processing as auth error

[Jeff Layton]

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@vger.kernel.org
Fixes: 29cd2927fb91 ("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>
---
This should be more correct. Unfortunately, I don't know of any
testcases for low-level RPC error handling. That seems like something
that would be nice to do with pynfs or similar though.
---
 net/sunrpc/svc.c | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 939b6239df8ab6229ce34836d77d3a6b983fbbb7..99050ab1435148ac5d52b697ab1a771b9e948143 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -1375,7 +1375,8 @@ svc_process_common(struct svc_rqst *rqstp)
 	case SVC_OK:
 		break;
 	case SVC_GARBAGE:
-		goto err_garbage_args;
+		rqstp->rq_auth_stat = rpc_autherr_badcred;
+		goto err_bad_auth;
 	case SVC_SYSERR:
 		goto err_system_err;
 	case SVC_DENIED:
@@ -1516,14 +1517,6 @@ svc_process_common(struct svc_rqst *rqstp)
 	*rqstp->rq_accept_statp = rpc_proc_unavail;
 	goto sendit;
 
-err_garbage_args:
-	svc_printk(rqstp, "failed to decode RPC header\n");
-
-	if (serv->sv_stats)
-		serv->sv_stats->rpcbadfmt++;
-	*rqstp->rq_accept_statp = rpc_garbage_args;
-	goto sendit;
-
 err_system_err:
 	if (serv->sv_stats)
 		serv->sv_stats->rpcbadfmt++;

---
base-commit: 9afe652958c3ee88f24df1e4a97f298afce89407
change-id: 20250617-rpc-6-16-cc7a23e9c961

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

Re: [PATCH] sunrpc: handle SVC_GARBAGE during svc auth processing as auth error

[Chuck Lever]

From: Chuck Lever <chuck.lever@oracle.com>

On Thu, 19 Jun 2025 06:01:55 -0400, Jeff Layton wrote:
> 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.
> 
> [...]

Yesterday's version passed overnight CI testing.

Applied to nfsd-fixes, thanks!

[1/1] sunrpc: handle SVC_GARBAGE during svc auth processing as auth error
      commit: 92c2969bcd57272698d5aae037f55481dcb11f2d

--
Chuck Lever