[PATCH 6.6.y] nfsd: size fh_verify server sockaddr slot by xpt_locallen

[Sasha Levin <sashal@kernel.org>]

From: Chris Mason <clm@meta.com>

[ Upstream commit 71d068490098b1d23c63b2345e40675d3a1ca763 ]

The nfsd_fh_verify and nfsd_fh_verify_err tracepoints declare the
server sockaddr slot sized by xpt_remotelen but fill it from
xpt_local using xpt_locallen:

    TP_STRUCT__entry(
            ...
            __sockaddr(server, rqstp->rq_xprt->xpt_remotelen)
            ...
    )
    TP_fast_assign(
            ...
            __assign_sockaddr(server, &rqstp->rq_xprt->xpt_local,
                              rqstp->rq_xprt->xpt_locallen);
            ...
    )

When xpt_locallen exceeds xpt_remotelen, __assign_sockaddr's memcpy
writes past the reserved ring-buffer slot. In the reverse direction
(xpt_locallen < xpt_remotelen) the slot is oversized and the
unwritten tail leaks prior ring-buffer contents to trace consumers.

The write-past-end case is reachable on NFS/UDP. svc_xprt_set_remote()
is only called from svc_tcp_accept() (net/sunrpc/svcsock.c) and from
the RDMA connect path; svc_create_socket() for UDP calls only
svc_xprt_set_local(), so xpt_remotelen stays 0 for the xprt's
lifetime. Every fh_verify trace for an NFSv2/v3-over-UDP request
then copies 16 or 28 bytes from xpt_local into a zero-byte slot.

The other NFSD tracepoints that record the server address
(NFSD_TRACE_PROC_CALL_FIELDS, NFSD_TRACE_PROC_RES_FIELDS,
SVC_RQST_ENDPOINT_FIELDS) already size the server slot by
xpt_locallen; nfsd_fh_verify and nfsd_fh_verify_err were the only
exceptions.

Fix by sizing the server slot with xpt_locallen so the declared slot
matches the copy length. The client slot and its assignment already
agree on xpt_remotelen and are left untouched.

Fixes: 051382885552 ("NFSD: Instrument fh_verify()")
Fixes: 948755efc951 ("NFSD: Replace dprintk() call site in fh_verify()")
Cc: stable@vger.kernel.org
Assisted-by: kres:claude-opus-4-7
Signed-off-by: Chris Mason <clm@meta.com>
Link: https://patch.msgid.link/20260531-nfsd-testing-v1-1-7bfa481b0540@kernel.org
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/nfsd/trace.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
index d7ed49eef5911..6e57a9dba1a59 100644
--- a/fs/nfsd/trace.h
+++ b/fs/nfsd/trace.h
@@ -201,7 +201,7 @@ TRACE_EVENT(nfsd_fh_verify,
 	TP_ARGS(rqstp, fhp, type, access),
 	TP_STRUCT__entry(
 		__field(unsigned int, netns_ino)
-		__sockaddr(server, rqstp->rq_xprt->xpt_remotelen)
+		__sockaddr(server, rqstp->rq_xprt->xpt_locallen)
 		__sockaddr(client, rqstp->rq_xprt->xpt_remotelen)
 		__field(u32, xid)
 		__field(u32, fh_hash)
@@ -240,7 +240,7 @@ TRACE_EVENT_CONDITION(nfsd_fh_verify_err,
 	TP_CONDITION(error),
 	TP_STRUCT__entry(
 		__field(unsigned int, netns_ino)
-		__sockaddr(server, rqstp->rq_xprt->xpt_remotelen)
+		__sockaddr(server, rqstp->rq_xprt->xpt_locallen)
 		__sockaddr(client, rqstp->rq_xprt->xpt_remotelen)
 		__field(u32, xid)
 		__field(u32, fh_hash)
-- 
2.53.0