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authorJonathon Reinhart <jonathon.reinhart@gmail.com>2021-05-01 04:28:22 -0400
committerDavid S. Miller <davem@davemloft.net>2021-05-04 11:58:28 -0700
commit8d432592f30fcc34ef5a10aac4887b4897884493 (patch)
treeafec67dce49a4a74ded0a415c55281bcfcb44e4b
parent1682d8df20aa505f6ab12c76e934b26ede39c529 (diff)
net: Only allow init netns to set default tcp cong to a restricted algo
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: 97684f0970f6 ("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: 6670e1524477 ("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>
-rw-r--r--net/ipv4/tcp_cong.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index 563d016e7478..db5831e6c136 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -230,6 +230,10 @@ int tcp_set_default_congestion_control(struct net *net, const char *name)
ret = -ENOENT;
} else if (!bpf_try_module_get(ca, ca->owner)) {
ret = -EBUSY;
+ } else if (!net_eq(net, &init_net) &&
+ !(ca->flags & TCP_CONG_NON_RESTRICTED)) {
+ /* Only init netns can set default to a restricted algorithm */
+ ret = -EPERM;
} else {
prev = xchg(&net->ipv4.tcp_congestion_control, ca);
if (prev)