[PATCH] nfsd: clear XDR padding in GETXATTR replies

[Aldo Ariel Panzardo <qwe.aldo@gmail.com>]

nfsd4_vbuf_to_stream() uses a raw memcpy() for the first fragment of an
attribute value. xdr_reserve_space() aligns the reservation but does not
initialize the extra bytes. If the complete value fits in that fragment,
the loop that clears padding for the final fragment is never entered.

A remote client reading an attribute whose length is not a multiple of
four can therefore receive one to three stale bytes from the response
page.

Encode the first fragment with xdr_encode_opaque_fixed(), matching the
final-fragment path and ensuring that any XDR padding is zeroed.

Fixes: 23e50fe3a5e6 ("nfsd: implement the xattr functions and en/decode logic")
Cc: stable@vger.kernel.org
Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@gmail.com>
---
 fs/nfsd/nfs4xdr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index e17488a911..51ab68ffdf 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -5953,7 +5953,7 @@ nfsd4_vbuf_to_stream(struct xdr_stream *xdr, char *buf, u32 buflen)
 	if (!p)
 		return nfserr_resource;
 
-	memcpy(p, buf, cplen);
+	xdr_encode_opaque_fixed(p, buf, cplen);
 	buf += cplen;
 	buflen -= cplen;
 
-- 
2.43.0