title: net: Only allow init netns to set default tcp cong to a restricted algo
description: In the Linux kernel, the following vulnerability has been resolved:
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
affected:
{
product: Linux
vendor: Linux
defaultStatus: unaffected
repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
versions:
version: 6670e1524477, lessThan: 992de06308d9, status: affected, versionType: git
version: 6670e1524477, lessThan: 9884f745108f, status: affected, versionType: git
version: 6670e1524477, lessThan: 6c1ea8bee75d, status: affected, versionType: git
version: 6670e1524477, lessThan: efe1532a6e1a, status: affected, versionType: git
version: 6670e1524477, lessThan: e7d7bedd507b, status: affected, versionType: git
version: 6670e1524477, lessThan: 8d432592f30f, status: affected, versionType: git
}
{
product: Linux
vendor: Linux
defaultStatus: affected
repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
versions:
version: 4.15, status: affected
version: 0, lessThan: 4.15, status: unaffected, versionType: custom
version: 4.19.191, lessThanOrEqual: 4.19.*, status: unaffected, versionType: custom
version: 5.4.119, lessThanOrEqual: 5.4.*, status: unaffected, versionType: custom
version: 5.10.37, lessThanOrEqual: 5.10.*, status: unaffected, versionType: custom
version: 5.11.21, lessThanOrEqual: 5.11.*, status: unaffected, versionType: custom
version: 5.12.4, lessThanOrEqual: 5.12.*, status: unaffected, versionType: custom
version: 5.13, lessThanOrEqual: *, status: unaffected, versionType: original_commit_for_fix
}
