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net: Only allow init netns to set default tcp cong to a restricted algo
commit8d432592f3
upstream. tcp_set_default_congestion_control() is netns-safe in that it writes to &net->ipv4.tcp_congestion_control, but it also sets ca->flags |= TCP_CONG_NON_RESTRICTED which is not namespaced. This has the unintended side-effect of changing the global net.ipv4.tcp_allowed_congestion_control sysctl, despite the fact that it is read-only:97684f0970
("net: Make tcp_allowed_congestion_control readonly in non-init netns") Resolve this netns "leak" by only allowing the init netns to set the default algorithm to one that is restricted. This restriction could be removed if tcp_allowed_congestion_control were namespace-ified in the future. This bug was uncovered with https://github.com/JonathonReinhart/linux-netns-sysctl-verify Fixes:6670e15244
("tcp: Namespace-ify sysctl_tcp_default_congestion_control") Signed-off-by: Jonathon Reinhart <jonathon.reinhart@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -230,6 +230,10 @@ int tcp_set_default_congestion_control(struct net *net, const char *name)
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ret = -ENOENT;
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} else if (!bpf_try_module_get(ca, ca->owner)) {
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ret = -EBUSY;
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} else if (!net_eq(net, &init_net) &&
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!(ca->flags & TCP_CONG_NON_RESTRICTED)) {
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/* Only init netns can set default to a restricted algorithm */
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ret = -EPERM;
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} else {
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prev = xchg(&net->ipv4.tcp_congestion_control, ca);
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if (prev)
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