Patchwork ifname=xxx for -netdev bridge

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Submitter Alexandre Kandalintsev
Date March 21, 2013, 6:05 p.m.
Message ID <20130321190509.6e1d73e5@messir.net>
Download mbox | patch
Permalink /patch/229790/
State New
Headers show

Comments

Alexandre Kandalintsev - March 21, 2013, 6:05 p.m.
Hi!


Here is the patch that allows us to specify the name of tap interface
when -netdev bridge is used. It's like -netdev tap,ifname=xxx, but for
bridges.


** Motivation **

We've got zillions of VMs and would like to see meaningful names of tap
interfaces. This is really useful for for, e.g., system administrators
in case they want to run tcpdump on it.


** How it works **

Just specify a ifname= parameter as it is done if --netdev tap is used.
However, as it requires root privs, the interface renaming is
actually done by qemu-bridge-helper. --netdev tap,ifname=xxx will fail
if qemu is launched not from root.


** TODO **

1. Update docs
2. I'm afraid that net_init_tap should not run helper with
--br=DEFAULT_BRIDGE_INTERFACE . At least bridge name should be tunnable.
But this is a future work.
3. May be we should call qemu-bridge-helper for tap interface renamings
because it always has root privs?


From 079027fe3696de2e2adc8e60377b995dd9548eac Mon Sep 17 00:00:00 2001
From: Alexandre Kandalintsev <spam@messir.net>
Date: Thu, 21 Mar 2013 18:48:12 +0100
Subject: [PATCH] added support for ifname in -netdev bridge


Signed-off-by: Alexandre Kandalintsev <spam@messir.net>
---
 include/net/net.h    |  1 +
 net/tap.c            | 25 ++++++++++++++++---------
 qapi-schema.json     |  1 +
 qemu-bridge-helper.c | 12 ++++++++++--
 4 files changed, 28 insertions(+), 11 deletions(-)
Eric Blake - March 21, 2013, 6:57 p.m.
On 03/21/2013 12:05 PM, Alexandre Kandalintsev wrote:
> Hi!
> 
> 
> Here is the patch that allows us to specify the name of tap interface
> when -netdev bridge is used. It's like -netdev tap,ifname=xxx, but for
> bridges.
> 

> +++ b/qapi-schema.json
> @@ -2676,6 +2676,7 @@
>  { 'type': 'NetdevBridgeOptions',
>    'data': {
>      '*br':     'str',
> +    '*ifname': 'str',
>      '*helper': 'str' } }

You also need to add a line documenting this field:

# @ifname: #optional Set the interface name that will be used (since 1.5).
Stefan Hajnoczi - March 25, 2013, 9:03 a.m.
On Thu, Mar 21, 2013 at 07:05:09PM +0100, Alexandre Kandalintsev wrote:
> Hi!
> 
> 
> Here is the patch that allows us to specify the name of tap interface
> when -netdev bridge is used. It's like -netdev tap,ifname=xxx, but for
> bridges.
> 
> 
> ** Motivation **
> 
> We've got zillions of VMs and would like to see meaningful names of tap
> interfaces. This is really useful for for, e.g., system administrators
> in case they want to run tcpdump on it.
> 
> 
> ** How it works **
> 
> Just specify a ifname= parameter as it is done if --netdev tap is used.
> However, as it requires root privs, the interface renaming is
> actually done by qemu-bridge-helper. --netdev tap,ifname=xxx will fail
> if qemu is launched not from root.
> 
> 
> ** TODO **
> 
> 1. Update docs
> 2. I'm afraid that net_init_tap should not run helper with
> --br=DEFAULT_BRIDGE_INTERFACE . At least bridge name should be tunnable.
> But this is a future work.
> 3. May be we should call qemu-bridge-helper for tap interface renamings
> because it always has root privs?

qemu-bridge-helper is a setuid root binary.  It allows access to things
an unprivileged user normally cannot do.  We need to be very careful
that new features cannot be abused.

There needs to be a policy in qemu-bridge-helper to control network
interface naming.

Imagine an existing qemu-bridge-helper deployment.  Now if your patch is
merged and the new qemu-bridge-helper is installed, unprivileged users
can create arbitrarily named network interfaces.

It was previously not possible to create arbitrarily named network
interfaces.  This might pose a security problem given firewall
configuration, monitoring software, etc which isn't configured to deal
with these new interface names.

By default, custom names should not be allowed.  Perhaps the
qemu-bridge-helper configuration file needs an option to specify a glob
pattern, e.g. vm*.

This way the host system administrator can restrict network interface
names while still allowing humand-friendly names.

Stefan
Alexandre Kandalintsev - March 25, 2013, 9:28 p.m.
> By default, custom names should not be allowed.  Perhaps the
> qemu-bridge-helper configuration file needs an option to specify a
> glob pattern, e.g. vm*.
> 
> This way the host system administrator can restrict network interface
> names while still allowing humand-friendly names.

Ok, lets go this way. We will define patterns in bridge.conf like
~~~
allowifname vm*
~~~

--
Alexandre Kandalintsev
William Dauchy - Jan. 14, 2014, 6:39 p.m.
Hi Alexandre,

On Mon, Mar 25, 2013 at 10:28 PM, Alexandre Kandalintsev
<spam@messir.net> wrote:
> Ok, lets go this way. We will define patterns in bridge.conf like
> ~~~
> allowifname vm*
> ~~~

Do you have any news about this patch?

Regards,
Alexandre Kandalintsev - Jan. 20, 2014, 9:23 p.m.
Hi William,

I was worried that the amount of changes would
turn the maintainers away from the patch.

Another problem is that I think there is little demand
for this patch.

But let's try to push it once again. Give me a week or
two and I'll submit a new version.

--
best regards,
Alexandre


> Hi Alexandre,
> 
> On Mon, Mar 25, 2013 at 10:28 PM, Alexandre Kandalintsev
> <spam@messir.net> wrote:
> > Ok, lets go this way. We will define patterns in bridge.conf like
> > ~~~
> > allowifname vm*
> > ~~~
> 
> Do you have any news about this patch?
> 
> Regards,
William Dauchy - Jan. 23, 2014, 2:30 p.m.
On Mon, Jan 20, 2014 at 10:23 PM, Alexandre Kandalintsev
<spam@messir.net> wrote:
> I was worried that the amount of changes would
> turn the maintainers away from the patch.
>
> Another problem is that I think there is little demand
> for this patch.
>
> But let's try to push it once again. Give me a week or
> two and I'll submit a new version.

ack; please cc me when re-submitting.

Thanks,

Patch

diff --git a/include/net/net.h b/include/net/net.h
index cb049a1..4b25eb5 100644
--- a/include/net/net.h
+++ b/include/net/net.h
@@ -172,6 +172,7 @@  NetClientState *net_hub_port_find(int hub_id);
 #define DEFAULT_NETWORK_DOWN_SCRIPT "/etc/qemu-ifdown"
 #define DEFAULT_BRIDGE_HELPER CONFIG_QEMU_HELPERDIR "/qemu-bridge-helper"
 #define DEFAULT_BRIDGE_INTERFACE "br0"
+#define DEFAULT_BRIDGE_IFNAME "tap%d"
 
 void qdev_set_nic_properties(DeviceState *dev, NICInfo *nd);
 
diff --git a/net/tap.c b/net/tap.c
index daab350..d2e4bfc 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -424,11 +424,11 @@  static int recv_fd(int c)
     return len;
 }
 
-static int net_bridge_run_helper(const char *helper, const char *bridge)
+static int net_bridge_run_helper(const char *helper, const char *bridge, const char *ifname)
 {
     sigset_t oldmask, mask;
     int pid, status;
-    char *args[5];
+    char *args[6];
     char **parg;
     int sv[2];
 
@@ -446,6 +446,7 @@  static int net_bridge_run_helper(const char *helper, const char *bridge)
         int open_max = sysconf(_SC_OPEN_MAX), i;
         char fd_buf[6+10];
         char br_buf[6+IFNAMSIZ] = {0};
+        char ifname_buf[9+IFNAMSIZ] = {0};
         char helper_cmd[PATH_MAX + sizeof(fd_buf) + sizeof(br_buf) + 15];
 
         for (i = 0; i < open_max; i++) {
@@ -459,6 +460,10 @@  static int net_bridge_run_helper(const char *helper, const char *bridge)
 
         snprintf(fd_buf, sizeof(fd_buf), "%s%d", "--fd=", sv[1]);
 
+        if (ifname) {
+          snprintf(ifname_buf, sizeof(ifname_buf), "%s%s", "--ifname=", ifname);
+        }
+
         if (strrchr(helper, ' ') || strrchr(helper, '\t')) {
             /* assume helper is a command */
 
@@ -466,8 +471,8 @@  static int net_bridge_run_helper(const char *helper, const char *bridge)
                 snprintf(br_buf, sizeof(br_buf), "%s%s", "--br=", bridge);
             }
 
-            snprintf(helper_cmd, sizeof(helper_cmd), "%s %s %s %s",
-                     helper, "--use-vnet", fd_buf, br_buf);
+            snprintf(helper_cmd, sizeof(helper_cmd), "%s %s %s %s %s",
+                     helper, "--use-vnet", fd_buf, br_buf, ifname_buf);
 
             parg = args;
             *parg++ = (char *)"sh";
@@ -486,6 +491,7 @@  static int net_bridge_run_helper(const char *helper, const char *bridge)
             *parg++ = (char *)"--use-vnet";
             *parg++ = fd_buf;
             *parg++ = br_buf;
+            *parg++ = ifname_buf;
             *parg++ = NULL;
 
             execv(helper, args);
@@ -524,7 +530,7 @@  int net_init_bridge(const NetClientOptions *opts, const char *name,
                     NetClientState *peer)
 {
     const NetdevBridgeOptions *bridge;
-    const char *helper, *br;
+    const char *helper, *br, *ifname;
 
     TAPState *s;
     int fd, vnet_hdr;
@@ -534,8 +540,9 @@  int net_init_bridge(const NetClientOptions *opts, const char *name,
 
     helper = bridge->has_helper ? bridge->helper : DEFAULT_BRIDGE_HELPER;
     br     = bridge->has_br     ? bridge->br     : DEFAULT_BRIDGE_INTERFACE;
+    ifname = bridge->has_ifname ? bridge->ifname : DEFAULT_BRIDGE_IFNAME;
 
-    fd = net_bridge_run_helper(helper, br);
+    fd = net_bridge_run_helper(helper, br, ifname);
     if (fd == -1) {
         return -1;
     }
@@ -686,11 +693,12 @@  int net_init_tap(const NetClientOptions *opts, const char *name,
     const char *script = NULL; /* suppress wrong "uninit'd use" gcc warning */
     const char *downscript = NULL;
     const char *vhostfdname;
+    const char *br;
     char ifname[128];
 
     assert(opts->kind == NET_CLIENT_OPTIONS_KIND_TAP);
     tap = opts->tap;
-    queues = tap->has_queues ? tap->queues : 1;
+    queues      = tap->has_queues  ? tap->queues  : 1;
     vhostfdname = tap->has_vhostfd ? tap->vhostfd : NULL;
 
     /* QEMU vlans does not support multiqueue tap, in this case peer is set.
@@ -775,8 +783,7 @@  int net_init_tap(const NetClientOptions *opts, const char *name,
                          "queues=, and fds= are invalid with helper=");
             return -1;
         }
-
-        fd = net_bridge_run_helper(tap->helper, DEFAULT_BRIDGE_INTERFACE);
+        fd = net_bridge_run_helper(tap->helper, DEFAULT_BRIDGE_INTERFACE, NULL);
         if (fd == -1) {
             return -1;
         }
diff --git a/qapi-schema.json b/qapi-schema.json
index fdaa9da..700e781 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -2676,6 +2676,7 @@ 
 { 'type': 'NetdevBridgeOptions',
   'data': {
     '*br':     'str',
+    '*ifname': 'str',
     '*helper': 'str' } }
 
 ##
diff --git a/qemu-bridge-helper.c b/qemu-bridge-helper.c
index 287bfd5..39486b1 100644
--- a/qemu-bridge-helper.c
+++ b/qemu-bridge-helper.c
@@ -67,7 +67,7 @@  typedef QSIMPLEQ_HEAD(ACLList, ACLRule) ACLList;
 static void usage(void)
 {
     fprintf(stderr,
-            "Usage: qemu-bridge-helper [--use-vnet] --br=bridge --fd=unixfd\n");
+            "Usage: qemu-bridge-helper [--use-vnet] [--ifname=name] --br=bridge --fd=unixfd\n");
 }
 
 static int parse_acl_file(const char *filename, ACLList *acl_list)
@@ -233,6 +233,7 @@  int main(int argc, char **argv)
     int use_vnet = 0;
     int mtu;
     const char *bridge = NULL;
+    const char *ifname = NULL;
     char iface[IFNAMSIZ];
     int index;
     ACLRule *acl_rule;
@@ -259,6 +260,8 @@  int main(int argc, char **argv)
             bridge = &argv[index][5];
         } else if (strncmp(argv[index], "--fd=", 5) == 0) {
             unixfd = atoi(&argv[index][5]);
+        } else if (strncmp(argv[index], "--ifname=", 9) == 0) {
+            ifname = &argv[index][9];
         } else {
             usage();
             return EXIT_FAILURE;
@@ -330,7 +333,12 @@  int main(int argc, char **argv)
 
     /* request a tap device, disable PI, and add vnet header support if
      * requested and it's available. */
-    prep_ifreq(&ifr, "tap%d");
+    if (ifname) {
+      /* prep_ifreq will truncate the name if it is too long */
+      prep_ifreq(&ifr, ifname);
+    } else {
+      prep_ifreq(&ifr, "tap%d");
+    }
     ifr.ifr_flags = IFF_TAP|IFF_NO_PI;
     if (use_vnet && has_vnet_hdr(fd)) {
         ifr.ifr_flags |= IFF_VNET_HDR;