CVE-2025-38089: sunrpc: handle SVC_GARBAGE during svc auth processing as auth error

In the Linux kernel, the following vulnerability has been resolved:

sunrpc: handle SVCGARBAGE during svc auth processing as auth error

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 SVCGARBAGE is returned without setting the rqacceptstatp 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 SVCGARBAGE return from svcauthenticate or pgauthenticate as if it should send a GARBAGEARGS reply. RFC 5531 says that if authentication fails that the RPC should be rejected instead with a status of AUTHERR.

Handle a SVCGARBAGE return as an AUTHERROR, with a reason of AUTHBADCRED instead of returning GARBAGEARGS in that case. This sidesteps the whole problem of touching the rpcacceptstatp pointer in this situation and avoids the crash.