[PATCH 5.9 169/255] NFS: Fix listxattr receive buffer size

[Greg Kroah-Hartman]

From: Chuck Lever <chuck.lever@xxxxxxxxxx>

[ Upstream commit 6c2190b3fcbc92cb79e39cc7e7531656b341e463 ]

Certain NFSv4.2/RDMA tests fail with v5.9-rc1.

rpcrdma_convert_kvec() runs off the end of the rl_segments array
because rq_rcv_buf.tail[0].iov_len holds a very large positive
value. The resultant kernel memory corruption is enough to crash
the client system.

Callers of rpc_prepare_reply_pages() must reserve an extra XDR_UNIT
in the maximum decode size for a possible XDR pad of the contents
of the xdr_buf's pages. That guarantees the allocated receive buffer
will be large enough to accommodate the usual contents plus that XDR
pad word.

encode_op_hdr() cannot add that extra word. If it does,
xdr_inline_pages() underruns the length of the tail iovec.

Fixes: 3e1f02123fba ("NFSv4.2: add client side XDR handling for extended attributes")
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
Signed-off-by: Anna Schumaker <Anna.Schumaker@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/nfs/nfs42xdr.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/nfs/nfs42xdr.c b/fs/nfs/nfs42xdr.c
index cc50085e151c5..d0ddf90c9be48 100644
--- a/fs/nfs/nfs42xdr.c
+++ b/fs/nfs/nfs42xdr.c
@@ -179,7 +179,7 @@
 				 1 + nfs4_xattr_name_maxsz + 1)
 #define decode_setxattr_maxsz   (op_decode_hdr_maxsz + decode_change_info_maxsz)
 #define encode_listxattrs_maxsz  (op_encode_hdr_maxsz + 2 + 1)
-#define decode_listxattrs_maxsz  (op_decode_hdr_maxsz + 2 + 1 + 1)
+#define decode_listxattrs_maxsz  (op_decode_hdr_maxsz + 2 + 1 + 1 + 1)
 #define encode_removexattr_maxsz (op_encode_hdr_maxsz + 1 + \
 				  nfs4_xattr_name_maxsz)
 #define decode_removexattr_maxsz (op_decode_hdr_maxsz + \
@@ -504,7 +504,7 @@ static void encode_listxattrs(struct xdr_stream *xdr,
 {
 	__be32 *p;
 
-	encode_op_hdr(xdr, OP_LISTXATTRS, decode_listxattrs_maxsz + 1, hdr);
+	encode_op_hdr(xdr, OP_LISTXATTRS, decode_listxattrs_maxsz, hdr);
 
 	p = reserve_space(xdr, 12);
 	if (unlikely(!p))
-- 
2.27.0