[Qemu-devel] [PATCHv2 4/4] Warning messages on net devices hotplug

[Eduardo Otubo <otubo@linux.vnet.ibm.com>]

With the inclusion of the new "double whitelist" seccomp filter, Qemu
won't be able to execve() in runtime, thus, no hotplug net devices
allowed.

v2: * Error messages moved to the backend function, net_init_tap(), recommended
      by Paolo Bonzini
    * Documentation added to QMP and HMP commands, and also to the Qemu options.

Signed-off-by: Eduardo Otubo <otubo@linux.vnet.ibm.com>
---
 hmp-commands.hx | 4 ++--
 net.c           | 1 +
 net/tap.c       | 5 +++++
 qemu-options.hx | 3 ++-
 qmp-commands.hx | 3 ++-
 5 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/hmp-commands.hx b/hmp-commands.hx
index e0b537d..3e28501 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -1068,7 +1068,7 @@ ETEXI
         .name       = "host_net_add",
         .args_type  = "device:s,opts:s?",
         .params     = "tap|user|socket|vde|dump [options]",
-        .help       = "add host VLAN client",
+        .help       = "add host VLAN client, feature disabled when -sandbox is in use",
         .mhandler.cmd = net_host_device_add,
     },
 
@@ -1096,7 +1096,7 @@ ETEXI
         .name       = "netdev_add",
         .args_type  = "netdev:O",
         .params     = "[user|tap|socket],id=str[,prop=value][,...]",
-        .help       = "add host network device",
+        .help       = "add host network device, feature disabled when -sandbox is in use",
         .mhandler.cmd = hmp_netdev_add,
     },
 
diff --git a/net.c b/net.c
index ae4bc0d..02188f0 100644
--- a/net.c
+++ b/net.c
@@ -765,6 +765,7 @@ void net_host_device_add(Monitor *mon, const QDict *qdict)
     qemu_opt_set(opts, "type", device);
 
     net_client_init(opts, 0, &local_err);
+
     if (error_is_set(&local_err)) {
         qerror_report_err(local_err);
         error_free(local_err);
diff --git a/net/tap.c b/net/tap.c
index df89caa..dd8c79b 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -590,6 +590,11 @@ static int net_tap_init(const NetdevTapOptions *tap, int *vnet_hdr,
 int net_init_tap(const NetClientOptions *opts, const char *name,
                  NetClientState *peer)
 {
+#ifdef CONFIG_SECCOMP
+    error_report("Cannot hotplug TAP device when -sandbox is in effect");
+    return -1;
+#endif
+
     const NetdevTapOptions *tap;
 
     int fd, vnet_hdr = 0;
diff --git a/qemu-options.hx b/qemu-options.hx
index 7d97f96..02afba3 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -2767,7 +2767,8 @@ STEXI
 @item -sandbox
 @findex -sandbox
 Enable Seccomp mode 2 system call filter. 'on' will enable syscall filtering and 'off' will
-disable it.  The default is 'off'.
+disable it.  The default is 'on'. Note that when using the '-sandbox on' option the hot plug
+of new devices will be disabled.
 ETEXI
 
 DEF("readconfig", HAS_ARG, QEMU_OPTION_readconfig,
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 2f8477e..cccb8f1 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -757,7 +757,8 @@ Example:
 
 Note: The supported device options are the same ones supported by the '-net'
       command-line argument, which are listed in the '-help' output or QEMU's
-      manual
+      manual. Also note that the hot plug is disabled when -sandbox is in
+      effect
 
 EQMP
 
-- 
1.7.12