ipv6: Fix dst leak for uncached routes.

Overview

In the Linux kernel, the following vulnerability has been resolved:

ipv6: Fix dst leak for uncached routes.

ip6_route_output_flags(), ip6_rt_put_flags(), and ip6_dst_check() detect an uncached route by list_empty(&rt->dst.rt_uncached), which replaced the static DST_NOCACHE flag check in commit a4c2fd7f7891 ("net: remove DST_NOCACHE flag").

When a device is unregistered, rt6_uncached_list_flush_dev() unlinks uncached routes tied to the device from rt6_uncached_list.

Previously, they were moved to another list with list_move() (__list_del_entry() + list_add()), and since commit 98aa546af5e4 ("inet: remove (struct uncached_list)->quarantine"), the routes are just unlinked with list_del_init().

If list_del_init() runs concurrently, list_empty() evaluates to true; ip6_route_output_flags() calls dst_hold_safe() incorrectly and ip6_rt_put_flags() skips ip6_rt_put(), leaking dst, and thus dev tied via rt->from as well.

The same race is partially fixed by commit 9a6f0c4d5796 ("dst: fix races in rt6_uncached_list_del() and rt_del_uncached_list()").

Let's check rt6->dst.rt_uncached_list instead.

Note that IPv4 does not have the same issue.

Affected

• Linux >= 98aa546af5e4f180439c82da403cc77926d3953b < 5045aa25f3790dcdb158a58ac60ccf8da42959aa
• Linux >= 98aa546af5e4f180439c82da403cc77926d3953b < ed902d5546fb9c142b3216d8eec914fa1bc0aa80
• Linux >= 98aa546af5e4f180439c82da403cc77926d3953b < f9722746df13a8a29103c847ef56b02c11ce0963
• Linux >= 98aa546af5e4f180439c82da403cc77926d3953b < be31fe6333f534155e6b408f1ef6d77974bb41aa
• Linux 6.11

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.