[PULL 6/6] virtiofsd: drop all capabilities in the wait parent process

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: Stefan Hajnoczi <stefanha@redhat.com>

All this process does is wait for its child.  No capabilities are
needed.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 tools/virtiofsd/passthrough_ll.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index e49650b63d..3ba1d90984 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -2530,6 +2530,17 @@ static void print_capabilities(void)
     printf("}\n");
 }
 
+/*
+ * Drop all Linux capabilities because the wait parent process only needs to
+ * sit in waitpid(2) and terminate.
+ */
+static void setup_wait_parent_capabilities(void)
+{
+    capng_setpid(syscall(SYS_gettid));
+    capng_clear(CAPNG_SELECT_BOTH);
+    capng_apply(CAPNG_SELECT_BOTH);
+}
+
 /*
  * Move to a new mount, net, and pid namespaces to isolate this process.
  */
@@ -2563,6 +2574,8 @@ static void setup_namespaces(struct lo_data *lo, struct fuse_session *se)
         pid_t waited;
         int wstatus;
 
+        setup_wait_parent_capabilities();
+
         /* The parent waits for the child */
         do {
             waited = waitpid(child, &wstatus, 0);
-- 
2.26.2