ipv6: fix fib6 walker UAF on seq stop

ipv6_route_iter_active() treats a walker in FWS_U at the table root as
already unlinked. fib6_del_route() can move a still-linked walker into
that same state when the current leaf is the last route at the root,
so ipv6_route_native_seq_stop() skips fib6_walker_unlink(). The seq
private object can then be freed while it remains on
net->ipv6.fib6_walkers. A later route deletion walks the dangling list
and uses the freed walker.

Use the list head as membership state and reinitialize it when
unlinking. Keep the existing w->node check so a never-started iterator
with a zeroed private object is not treated as linked.

The same stop helper is used by /proc/net/ipv6_route and by the BPF
ipv6_route iterator. The BPF show path only widens the race.

Fixes: 8d2ca1d7b5c3 ("ipv6: avoid high order memory allocations for /proc/net/ipv6_route")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Co-developed-by: Luxing Yin <root@tr0jan.top>
Signed-off-by: Luxing Yin <root@tr0jan.top>
Signed-off-by: Zihan Xi <zihanx@nebusec.ai>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/89699735763f6c297584d7c2ff106239cc1e8ce0.1788837093.git.zihanx@nebusec.ai
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions