smb/client: avoid possible NULL dereference in cifs_free_subrequest()

Clang static checker (scan-build) warning:
	cifsglob.h:line 890, column 3
	Access to field 'ops' results in a dereference of a null pointer.

Commit 519be989717c ("cifs: Add a tracepoint to track credits involved in
R/W requests") adds a check for 'rdata->server', and let clang throw this
warning about NULL dereference.

When 'rdata->credits.value != 0 && rdata->server == NULL' happens,
add_credits_and_wake_if() will call rdata->server->ops->add_credits().
This will cause NULL dereference problem. Add a check for 'rdata->server'
to avoid NULL dereference.

Cc: stable@vger.kernel.org
Fixes: 69c3c023af25 ("cifs: Implement netfslib hooks")
Reviewed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Su Hui <suhui@nfschina.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c
index b2405dd4d4d4da6e515c554b9c3e9649ec59c4cb..45459af5044ddeeeb03ea16044bb8011bee6443d 100644 (file)
--- a/fs/smb/client/file.c
+++ b/fs/smb/client/file.c
@@ -315,7 +315,7 @@ static void cifs_free_subrequest(struct netfs_io_subrequest *subreq)
 #endif
        }
 
-       if (rdata->credits.value != 0)
+       if (rdata->credits.value != 0) {
                trace_smb3_rw_credits(rdata->rreq->debug_id,
                                      rdata->subreq.debug_index,
                                      rdata->credits.value,
@@ -323,8 +323,12 @@ static void cifs_free_subrequest(struct netfs_io_subrequest *subreq)
                                      rdata->server ? rdata->server->in_flight : 0,
                                      -rdata->credits.value,
                                      cifs_trace_rw_credits_free_subreq);
+               if (rdata->server)
+                       add_credits_and_wake_if(rdata->server, &rdata->credits, 0);
+               else
+                       rdata->credits.value = 0;
+       }
 
-       add_credits_and_wake_if(rdata->server, &rdata->credits, 0);
        if (rdata->have_xid)
                free_xid(rdata->xid);
 }