From f85dc137aabf357bf3d9fe4c9712121039d83798 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa Date: Mon, 17 Aug 2026 23:08:15 +0900 Subject: [PATCH] net: add missing ref_tracker_dir_exit() to net_passive_dec() I found that trying to read /sys/kernel/debug/ref_tracker/* causes NULL pointer dereference crash when alloc_netdev_mqs() via unshare() returned NULL, for commit 9ba74e6c9e9d ("net: add networking namespace refcount tracker") added ref_tracker_dir_exit(&net->refcnt_tracker) to only __put_net() path whereas commit 65b584f53611 ("ref_tracker: automatically register a file in debugfs for a ref_tracker_dir") added ref_tracker_dir_debugfs() to ref_tracker_dir_init() path. Since preinit_net() calls ref_tracker_dir_init(&net->refcnt_tracker) and ref_tracker_dir_init(&net->notrefcnt_tracker), we need to make sure that both ref_tracker_dir_exit(&net->refcnt_tracker) and ref_tracker_dir_exit(&net->notrefcnt_tracker) are called before net_passive_dec() schedules for kmem_cache_free() via net_complete_free(). ref_tracker_dir_exit(&net->refcnt_tracker) is called via put_net() when ns_ref_put() returned true. But put_net() is not called when copy_net_ns() fails. Therefore, call ref_tracker_dir_exit() from net_passive_dec() if put_net() is not yet called. Link: https://sashiko.dev/#/patchset/b06ce35d-e7bc-47a5-8e0a-e82be7e4dd08%40I-love.SAKURA.ne.jp Fixes: 9ba74e6c9e9d ("net: add networking namespace refcount tracker") Reviewed-by: Eric Dumazet Signed-off-by: Tetsuo Handa Link: https://patch.msgid.link/64254d80-9248-466c-8108-95f43bd71117@I-love.SAKURA.ne.jp Signed-off-by: Jakub Kicinski --- net/core/net_namespace.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c index a91d2b58aadd..9166f467293e 100644 --- a/net/core/net_namespace.c +++ b/net/core/net_namespace.c @@ -536,8 +536,12 @@ void net_passive_dec(struct net *net) if (refcount_dec_and_test(&net->passive)) { kfree(rcu_access_pointer(net->gen)); +#ifdef CONFIG_REF_TRACKER /* There should not be any trackers left there. */ ref_tracker_dir_exit(&net->notrefcnt_tracker); + if (!net->refcnt_tracker.dead) + ref_tracker_dir_exit(&net->refcnt_tracker); +#endif /* Wait for an extra rcu_barrier() before final free. */ llist_add(&net->defer_free_list, &defer_free_list);