600d14f83e
https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt: /proc/sys/net/ipv4/* Variables: ip_forward - BOOLEAN 0 - disabled (default) not 0 - enabled Forward Packets between interfaces. This variable is special, its change resets all configuration parameters to their default state (RFC1122 for hosts, RFC1812 for routers) /proc/sys/net/ipv4/ip_forward only does work when its value is changed and always returns the last written value. The last written value may not reflect the current state of the netstack (e.g. when `ip_forward` was written a value of "1" then disable forwarding on an interface) so there is no need for sentry to probe netstack to get the current forwarding state of interfaces. ``` ~$ cat /proc/sys/net/ipv4/ip_forward 0 ~$ sudo bash -c "echo 1 > /proc/sys/net/ipv4/ip_forward" ~$ cat /proc/sys/net/ipv4/ip_forward 1 ~$ sudo sysctl -a | grep ipv4 | grep forward net.ipv4.conf.all.forwarding = 1 net.ipv4.conf.default.forwarding = 1 net.ipv4.conf.eno1.forwarding = 1 net.ipv4.conf.lo.forwarding = 1 net.ipv4.conf.wlp1s0.forwarding = 1 net.ipv4.ip_forward = 1 net.ipv4.ip_forward_update_priority = 1 net.ipv4.ip_forward_use_pmtu = 0 ~$ sudo sysctl -w net.ipv4.conf.wlp1s0.forwarding=0 net.ipv4.conf.wlp1s0.forwarding = 0 ~$ sudo sysctl -a | grep ipv4 | grep forward net.ipv4.conf.all.forwarding = 1 net.ipv4.conf.default.forwarding = 1 net.ipv4.conf.eno1.forwarding = 1 net.ipv4.conf.lo.forwarding = 1 net.ipv4.conf.wlp1s0.forwarding = 0 net.ipv4.ip_forward = 1 net.ipv4.ip_forward_update_priority = 1 net.ipv4.ip_forward_use_pmtu = 0 ~$ cat /proc/sys/net/ipv4/ip_forward 1 ~$ sudo bash -c "echo 1 > /proc/sys/net/ipv4/ip_forward" ~$ sudo sysctl -a | grep ipv4 | grep forward net.ipv4.conf.all.forwarding = 1 net.ipv4.conf.default.forwarding = 1 net.ipv4.conf.eno1.forwarding = 1 net.ipv4.conf.lo.forwarding = 1 net.ipv4.conf.wlp1s0.forwarding = 0 net.ipv4.ip_forward = 1 net.ipv4.ip_forward_update_priority = 1 net.ipv4.ip_forward_use_pmtu = 0 ~$ sudo bash -c "echo 0 > /proc/sys/net/ipv4/ip_forward" ~$ sudo sysctl -a | grep ipv4 | grep forward sysctl: unable to open directory "/proc/sys/fs/binfmt_misc/" net.ipv4.conf.all.forwarding = 0 net.ipv4.conf.default.forwarding = 0 net.ipv4.conf.eno1.forwarding = 0 net.ipv4.conf.lo.forwarding = 0 net.ipv4.conf.wlp1s0.forwarding = 0 net.ipv4.ip_forward = 0 net.ipv4.ip_forward_update_priority = 1 net.ipv4.ip_forward_use_pmtu = 0 ~$ cat /proc/sys/net/ipv4/ip_forward 0 ``` In the above example we can see that writing "1" to /proc/sys/net/ipv4/ip_forward configures the stack to be a router (all interfaces are configured to enable forwarding). However, if we manually update an interace (`wlp1s0`) to not forward packets, /proc/sys/net/ipv4/ip_forward continues to return the last written value of "1", even though not all interfaces will forward packets. Also note that writing the same value twice has no effect; work is performed iff the value changes. This change also removes the 'unset' state from sentry's ip forwarding data structures as an 'unset' ip forwarding value is the same as leaving forwarding disabled as the stack is always brought up with forwarding initially disabled; disabling forwarding on a newly created stack is a no-op. PiperOrigin-RevId: 373853106 |
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| BUILD | ||
| context.go | ||
| inet.go | ||
| namespace.go | ||
| test_stack.go | ||