CVE-2026-98596ipv6: Fix dst leak for uncached routes.

Official description

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 packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/5045aa25f3790dcdb158a58ac60ccf8da42959aa
• https://git.kernel.org/stable/c/ed902d5546fb9c142b3216d8eec914fa1bc0aa80
• https://git.kernel.org/stable/c/f9722746df13a8a29103c847ef56b02c11ce0963
• https://git.kernel.org/stable/c/be31fe6333f534155e6b408f1ef6d77974bb41aa