NFS: Fix rpcrdma_inline_fixup() crash with new LISTXATTRS operation

By switching to an XFS-backed export, I am able to reproduce the
ibcomp worker crash on my client with xfstests generic/013.

For the failing LISTXATTRS operation, xdr_inline_pages() is called
with page_len=12 and buflen=128.

- When ->send_request() is called, rpcrdma_marshal_req() does not
  set up a Reply chunk because buflen is smaller than the inline
  threshold. Thus rpcrdma_convert_iovs() does not get invoked at
  all and the transport's XDRBUF_SPARSE_PAGES logic is not invoked
  on the receive buffer.

- During reply processing, rpcrdma_inline_fixup() tries to copy
  received data into rq_rcv_buf->pages because page_len is positive.
  But there are no receive pages because rpcrdma_marshal_req() never
  allocated them.

The result is that the ibcomp worker faults and dies. Sometimes that
causes a visible crash, and sometimes it results in a transport hang
without other symptoms.

RPC/RDMA's XDRBUF_SPARSE_PAGES support is not entirely correct, and
should eventually be fixed or replaced. However, my preference is
that upper-layer operations should explicitly allocate their receive
buffers (using GFP_KERNEL) when possible, rather than relying on
XDRBUF_SPARSE_PAGES.
Reported-by: Olga kornievskaia <kolga@netapp.com>
Suggested-by: Olga kornievskaia <kolga@netapp.com>
Fixes: c10a7514 ("NFSv4.2: add the extended attribute proc functions.")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Olga kornievskaia <kolga@netapp.com>
Reviewed-by: Frank van der Linden <fllinden@amazon.com>
Tested-by: Olga kornievskaia <kolga@netapp.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/nfs42proc.c

@@ -1241,12 +1241,13 @@ static ssize_t _nfs42_proc_listxattrs(struct inode *inode, void *buf,
 		.rpc_resp	= &res,
 	};
 	u32 xdrlen;
-	int ret, np;
+	int ret, np, i;
 
 
+	ret = -ENOMEM;
 	res.scratch = alloc_page(GFP_KERNEL);
 	if (!res.scratch)
-		return -ENOMEM;
+		goto out;
 
 	xdrlen = nfs42_listxattr_xdrsize(buflen);
 	if (xdrlen > server->lxasize)
@@ -1254,9 +1255,12 @@ static ssize_t _nfs42_proc_listxattrs(struct inode *inode, void *buf,
 	np = xdrlen / PAGE_SIZE + 1;
 
 	pages = kcalloc(np, sizeof(struct page *), GFP_KERNEL);
-	if (pages == NULL) {
-		__free_page(res.scratch);
-		return -ENOMEM;
+	if (!pages)
+		goto out_free_scratch;
+	for (i = 0; i < np; i++) {
+		pages[i] = alloc_page(GFP_KERNEL);
+		if (!pages[i])
+			goto out_free_pages;
 	}
 
 	arg.xattr_pages = pages;
@@ -1271,14 +1275,15 @@ static ssize_t _nfs42_proc_listxattrs(struct inode *inode, void *buf,
 		*eofp = res.eof;
 	}
 
+out_free_pages:
 	while (--np >= 0) {
 		if (pages[np])
 			__free_page(pages[np]);
 	}
-
-	__free_page(res.scratch);
 	kfree(pages);
-
+out_free_scratch:
+	__free_page(res.scratch);
+out:
 	return ret;
 
 }

fs/nfs/nfs42xdr.c

@@ -1528,7 +1528,6 @@ static void nfs4_xdr_enc_listxattrs(struct rpc_rqst *req,
 
 	rpc_prepare_reply_pages(req, args->xattr_pages, 0, args->count,
 	    hdr.replen);
-	req->rq_rcv_buf.flags |= XDRBUF_SPARSE_PAGES;
 
 	encode_nops(&hdr);
 }