SUNRPC: Fix a use after free bug with the NFSv4.1 backchannel

The ->release_request() callback was designed to allow the transport layer
to do housekeeping after the RPC call is done. It cannot be used to free
the request itself, and doing so leads to a use-after-free bug in
xprt_release().

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 9 insertions, 13 deletions

diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index 469de292c23c..42f09ade0044 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -46,6 +46,7 @@
 
 #include <linux/sunrpc/clnt.h>
 #include <linux/sunrpc/metrics.h>
+#include <linux/sunrpc/bc_xprt.h>
 
 #include "sunrpc.h"
 
@@ -1032,21 +1033,16 @@ void xprt_release(struct rpc_task *task)
         if (req->rq_release_snd_buf)
                 req->rq_release_snd_buf(req);
 
-        /*
-         * Early exit if this is a backchannel preallocated request.
-         * There is no need to have it added to the RPC slot list.
-         */
-        if (is_bc_request)
-                return;
-
-        memset(req, 0, sizeof(*req));   /* mark unused */
-
         dprintk("RPC: %5u release request %p\n", task->tk_pid, req);
+        if (likely(!is_bc_request)) {
+                memset(req, 0, sizeof(*req));   /* mark unused */
 
-        spin_lock(&xprt->reserve_lock);
-        list_add(&req->rq_list, &xprt->free);
-        rpc_wake_up_next(&xprt->backlog);
-        spin_unlock(&xprt->reserve_lock);
+                spin_lock(&xprt->reserve_lock);
+                list_add(&req->rq_list, &xprt->free);
+                rpc_wake_up_next(&xprt->backlog);
+                spin_unlock(&xprt->reserve_lock);
+        } else
+                xprt_free_bc_request(req);
 }
 
 /**