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ipv6: fix possible infinite loop in fib6_select_path()

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Found while auditing the same pattern Sashiko reported in
rt6_fill_node() [1]. Apply the same fix as
commit f8d8ce1b51 ("ipv6: fix possible infinite loop in fib6_info_uses_dev()").

Writers holding tb6_lock can list_del_rcu(&first->fib6_siblings)
without waiting for RCU readers; first->fib6_siblings.next then
still points into the old ring and this softirq-side walker never
reaches &first->fib6_siblings as its terminator. fib6_purge_rt()
always WRITE_ONCE()s first->fib6_nsiblings to 0 before
list_del_rcu(), so an inside-loop check is a reliable detach signal.

[1] https://sashiko.dev/#/patchset/20260526020227.4857-1-jiayuan.chen%40linux.dev

Fixes: d9ccb18f83 ("ipv6: Fix soft lockups in fib6_select_path under high next hop churn")
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20260527053133.180695-2-jiayuan.chen@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jiayuan Chen 2026-05-27 13:31:31 +08:00 committed by Jakub Kicinski
parent 9f72412bcf
commit 9c7da87c2d
1 changed files with 3 additions and 0 deletions
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3
net/ipv6/route.c
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@ -481,6 +481,9 @@ void fib6_select_path(const struct net *net, struct fib6_result *res,
const struct fib6_nh *nh = sibling->fib6_nh;
int nh_upper_bound;
if (!READ_ONCE(first->fib6_nsiblings))
break;
nh_upper_bound = atomic_read(&nh->fib_nh_upper_bound);
if (hash > nh_upper_bound)
continue;