[PATCH] nfsd: fix XDR padding calculation in ff_encode_getdeviceinfo

[Jeff Layton <jlayton@kernel.org>]

nfsd4_ff_encode_getdeviceinfo() computes the da_addr_body reservation
as 16 + netid_len + addr_len, but the subsequent xdr_encode_opaque()
calls emit 8 + round_up(netid_len, 4) + round_up(addr_len, 4) bytes.
The mismatch means the declared da_addr_body length exceeds the actual
encoded data by 2-8 bytes on every flexfile GETDEVICEINFO reply,
leaking stale reply-page content to the client and mis-aligning the
subsequent version list decode.

Use xdr_align_size() for each string length to match what
xdr_encode_opaque() actually writes.

Fixes: efcae97fa425 ("NFSD: da_addr_body field missing in some GETDEVICEINFO replies")
Assisted-by: kres:claude-opus-4-6
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/nfsd/flexfilelayoutxdr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/flexfilelayoutxdr.c b/fs/nfsd/flexfilelayoutxdr.c
index f9f7e38cba13..7f357dbd1bb1 100644
--- a/fs/nfsd/flexfilelayoutxdr.c
+++ b/fs/nfsd/flexfilelayoutxdr.c
@@ -94,7 +94,8 @@ nfsd4_ff_encode_getdeviceinfo(struct xdr_stream *xdr,
 	}
 
 	/* len + padding for two strings */
-	addr_len = 16 + da->netaddr.netid_len + da->netaddr.addr_len;
+	addr_len = 8 + xdr_align_size(da->netaddr.netid_len) +
+		   xdr_align_size(da->netaddr.addr_len);
 	ver_len = 20;
 
 	len = 4 + ver_len + 4 + addr_len;

---
base-commit: b69fc3eaa867d0caa904634ea7a1b4569411b163
change-id: 20260527-pnfs-fixes-23451bb03d57

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