Re: [libvirt] [PATCH v5] network: bridge: Don't start network if it collides with host routing

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 v3: Consider route netmask. Compare binary data rather than convert to string. v4: Return to using sscanf, drop inet functions in favor of virSocket, parsing safety checks. Don't make parse failures fatal, in case expected format changes. v5: Try and continue if we receive unexpected. Delimit parsed lines to prevent scanning past newline

+ while (cur) { + char iface[17], dest[128], mask[128]; + unsigned int addr_val, mask_val; + int num; + + /* NUL-terminate the line, so sscanf doesn't go beyond a newline. */ + char *nl = strchr(cur, '\n'); + if (nl) { + *nl++ = '\0'; + } + + num = sscanf(cur, "%16s %127s %*s %*s %*s %*s %*s %127s", + iface, dest, mask); + cur = nl;

+ if (num != 3) { + VIR_DEBUG("Failed to parse %s", PROC_NET_ROUTE); + continue; + }