[libvirt] [PATCH v2] network: bridge: Don't start network if it collides with host routing
Cole Robinson
crobinso at redhat.com
Wed May 26 19:56:17 UTC 2010
On 05/26/2010 02:05 PM, Laine Stump wrote:
> A couple items I didn't notice before:
>
> On 05/24/2010 02:52 PM, Cole Robinson wrote:
>> Fedora bug https://bugzilla.redhat.com/show_bug.cgi?id=235961
>>
>> If using the default virtual network, an easy way to lose guest network
>> connectivity is to install libvirt inside the VM. The autostarted
>> default network inside the guest collides with host virtual network
>> routing. This is a long standing issue that has caused users quite a
>> bit of pain and confusion.
>>
>> On network startup, parse /proc/net/route and compare the requested
>> IP+netmask against host routing destinations: if any matches are found,
>> refuse to start the network.
>>
>> v2: Drop sscanf, fix a comment typo, comment that function could use
>> libnl instead of /proc
>>
>> Signed-off-by: Cole Robinson<crobinso at redhat.com>
>> ---
>> src/network/bridge_driver.c | 102 +++++++++++++++++++++++++++++++++++++++++++
>> 1 files changed, 102 insertions(+), 0 deletions(-)
>>
>> diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c
>> index 5d7ef19..090bed7 100644
>> --- a/src/network/bridge_driver.c
>> +++ b/src/network/bridge_driver.c
>> @@ -42,6 +42,8 @@
>> #include<stdio.h>
>> #include<sys/wait.h>
>> #include<sys/ioctl.h>
>> +#include<netinet/in.h>
>> +#include<arpa/inet.h>
>>
>> #include "virterror_internal.h"
>> #include "datatypes.h"
>> @@ -908,6 +910,102 @@ cleanup:
>> return ret;
>> }
>>
>> +#define PROC_NET_ROUTE "/proc/net/route"
>> +
>> +/* XXX: This function can be a lot more exhaustive, there are certainly
>> + * other scenarios where we can ruin host network connectivity.
>> + * XXX: Using a proper library is preferred over parsing /proc
>> + */
>> +static int networkCheckRouteCollision(virNetworkObjPtr network)
>> +{
>> + int ret = -1, len;
>> + char *cur, *buf = NULL;
>> + enum {MAX_ROUTE_SIZE = 1024*64};
>> + struct in_addr inaddress, innetmask;
>> + char *netaddr = NULL;
>> +
>> + if (!network->def->ipAddress || !network->def->netmask)
>> + return 0;
>> +
>> + if (inet_pton(AF_INET, network->def->ipAddress,&inaddress)<= 0) {
>> + networkReportError(VIR_ERR_INTERNAL_ERROR,
>> + _("cannot parse IP address '%s'"),
>> + network->def->ipAddress);
>> + goto error;
>> + }
>> + if (inet_pton(AF_INET, network->def->netmask,&innetmask)<= 0) {
>> + networkReportError(VIR_ERR_INTERNAL_ERROR,
>> + _("cannot parse netmask '%s'"),
>> + network->def->netmask);
>> + goto error;
>> + }
>> +
>> + inaddress.s_addr&= innetmask.s_addr;
>> + netaddr = strdup(inet_ntoa(inaddress));
>>
>
> inet_ntoa() isn't threadsafe (it re-uses the same static buffer). strdup
> reduces the window, but the potential for a bad result is still there.
> Better to use inet_ntop(), or possibly use virSocketFormatAddr()
> (although that would have a bit of setup involved).
>
Will do.
> But since the string you're comparing it to below was also originally a
> binary value (and also converted with inet_ntoa(), maybe the best thing
> would be to just compare the binary values directly and avoid the
> conversion.
>
Doh, good point. I'll keep one of the inet_ntop conversions though, so
it can be used in error messages.
>> + if (!netaddr) {
>> + virReportOOMError();
>> + goto error;
>> + }
>> +
>> + /* Read whole routing table into memory */
>> + if ((len = virFileReadAll(PROC_NET_ROUTE, MAX_ROUTE_SIZE,&buf))< 0)
>> + goto error;
>> +
>> + /* Dropping the last character shouldn't hurt */
>> + buf[len-1] = '\0';
>> +
>> + /* First line is just headings, skip it */
>> + cur = strchr(buf, '\n');
>> +
>> + while (cur) {
>> + char *iface, *dest_raw;
>> + char *dest_ip;
>> + struct in_addr in;
>> + unsigned int addr_val;
>> +
>> + cur++;
>> +
>> + /* Delimit interface field */
>> + iface = cur;
>> + while(*cur> ' ') {
>> + cur++;
>> + }
>> + *cur++ = '\0';
>> +
>> + /* Delimit destination field */
>> + dest_raw = cur;
>> + while(*cur> ' ') {
>> + cur++;
>> + }
>> + *cur++ = '\0';
>> +
>> + if (virStrToLong_ui(dest_raw, NULL, 16,&addr_val)< 0) {
>> + networkReportError(VIR_ERR_INTERNAL_ERROR,
>> + _("Failed to convert network address %s"),
>> + dest_raw);
>> + goto error;
>> + }
>>
>
> After seeing the exchange with nDuff in #virt a couple days ago, it
> occurred to me that, in order to really check for an *exact* match of
> networks (and thus allow one to be a subset of the other, which can be a
> valid configuration), you should also parse further on in the line and
> get the netmask. Then compare netmasks of the two (as well as ANDing
> addr_val with the netmask to eliminate possibility of a network address
> that has extra bits set in the bottom).
>
Done, updated patch sent now.
Thanks,
Cole
More information about the libvir-list
mailing list