6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: James Chapman <jchapman@xxxxxxxxxxx> [ Upstream commit 5d066766c5f1252f98ff859265bcd1a5b52ac46c ] 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@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://syzkaller.appspot.com/bug?extid=332fe1e67018625f63c9 Fixes: 73d33bd063c4 ("l2tp: avoid using drain_workqueue in l2tp_pre_exit_net") Signed-off-by: James Chapman <jchapman@xxxxxxxxxxx> Link: https://patch.msgid.link/20241118140411.1582555-1-jchapman@xxxxxxxxxxx Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- net/l2tp/l2tp_core.c | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-) diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index 3eec23ac5ab10..369a2f2e459cd 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -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); } -- 2.43.0
