SUNRPC: Reinitialise the backchannel request buffers before reuse

stable inclusion
from stable-v4.19.256
commit 1429b2fa358c6fbd5e037edac59e20fa02aa783e
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5Q0SQ


CVE: NA

--------------------------------

commit 6622e3a73112fc336c1c2c582428fb5ef18e456a upstream.

When we're reusing the backchannel requests instead of freeing them,
then we should reinitialise any values of the send/receive xdr_bufs so
that they reflect the available space.

Fixes: 0d2a970d ("SUNRPC: Fix a backchannel race")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>

net/sunrpc/backchannel_rqst.c

@@ -69,6 +69,17 @@ static void xprt_free_allocation(struct rpc_rqst *req)
 	kfree(req);
 }
 
+static void xprt_bc_reinit_xdr_buf(struct xdr_buf *buf)
+{
+	buf->head[0].iov_len = PAGE_SIZE;
+	buf->tail[0].iov_len = 0;
+	buf->pages = NULL;
+	buf->page_len = 0;
+	buf->flags = 0;
+	buf->len = 0;
+	buf->buflen = PAGE_SIZE;
+}
+
 static int xprt_alloc_xdr_buf(struct xdr_buf *buf, gfp_t gfp_flags)
 {
 	struct page *page;
@@ -291,6 +302,9 @@ void xprt_free_bc_rqst(struct rpc_rqst *req)
 	 */
 	spin_lock_bh(&xprt->bc_pa_lock);
 	if (xprt_need_to_requeue(xprt)) {
+		xprt_bc_reinit_xdr_buf(&req->rq_snd_buf);
+		xprt_bc_reinit_xdr_buf(&req->rq_rcv_buf);
+		req->rq_rcv_buf.len = PAGE_SIZE;
 		list_add_tail(&req->rq_bc_pa_list, &xprt->bc_pa_list);
 		xprt->bc_alloc_count++;
 		req = NULL;