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

Signed-off-by: Stefan Hajnoczi <stefanha@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 af97ba1c41..0c3f33b074 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.
  */
@@ -2561,6 +2572,8 @@ 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);
-- 
2.25.1

On 4/16/20 6:49 PM, Stefan Hajnoczi wrote:
> All this process does is wait for its child.  No capabilities are
> needed.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@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 af97ba1c41..0c3f33b074 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));

Maybe worth a /* Drop all capabilities */ comment here.

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

> +    capng_clear(CAPNG_SELECT_BOTH);
> +    capng_apply(CAPNG_SELECT_BOTH);
> +}
> +
>   /*
>    * Move to a new mount, net, and pid namespaces to isolate this process.
>    */
> @@ -2561,6 +2572,8 @@ 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);
>