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net/l2tp: fix warning in l2tp_exit_net found by syzbot

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In l2tp's net exit handler, we check that an IDR is empty before
destroying it:

	WARN_ON_ONCE(!idr_is_empty(&pn->l2tp_tunnel_idr));
	idr_destroy(&pn->l2tp_tunnel_idr);

By forcing memory allocation failures in idr_alloc_32, syzbot is able
to provoke a condition where idr_is_empty returns false despite there
being no items in the IDR. This turns out to be because the radix tree
of the IDR contains only internal radix-tree nodes and it is this that
causes idr_is_empty to return false. The internal nodes are cleaned by
idr_destroy.

Use idr_for_each to check that the IDR is empty instead of
idr_is_empty to avoid the problem.

Reported-by: syzbot+332fe1e67018625f63c9@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=332fe1e67018625f63c9
Fixes: 73d33bd063 ("l2tp: avoid using drain_workqueue in l2tp_pre_exit_net")
Signed-off-by: James Chapman <jchapman@katalix.com>
Link: https://patch.msgid.link/20241118140411.1582555-1-jchapman@katalix.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
James Chapman 2024-11-18 14:04:11 +00:00 committed by Paolo Abeni
parent 9bb88c6596
commit 5d066766c5
1 changed files with 19 additions and 3 deletions
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22
net/l2tp/l2tp_core.c
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@ -1870,15 +1870,31 @@ static __net_exit void l2tp_pre_exit_net(struct net *net)
}
}
static int l2tp_idr_item_unexpected(int id, void *p, void *data)
{
const char *idr_name = data;
pr_err("l2tp: %s IDR not empty at net %d exit\n", idr_name, id);
WARN_ON_ONCE(1);
return 1;
}
static __net_exit void l2tp_exit_net(struct net *net)
{
struct l2tp_net *pn = l2tp_pernet(net);
WARN_ON_ONCE(!idr_is_empty(&pn->l2tp_v2_session_idr));
/* Our per-net IDRs should be empty. Check that is so, to
* help catch cleanup races or refcnt leaks.
*/
idr_for_each(&pn->l2tp_v2_session_idr, l2tp_idr_item_unexpected,
"v2_session");
idr_for_each(&pn->l2tp_v3_session_idr, l2tp_idr_item_unexpected,
"v3_session");
idr_for_each(&pn->l2tp_tunnel_idr, l2tp_idr_item_unexpected,
"tunnel");
idr_destroy(&pn->l2tp_v2_session_idr);
WARN_ON_ONCE(!idr_is_empty(&pn->l2tp_v3_session_idr));
idr_destroy(&pn->l2tp_v3_session_idr);
WARN_ON_ONCE(!idr_is_empty(&pn->l2tp_tunnel_idr));
idr_destroy(&pn->l2tp_tunnel_idr);
}