From d587d825424b6784ff7d7519efd1b827b09aa501 Mon Sep 17 00:00:00 2001 From: James Chapman Date: Thu, 18 Jul 2024 14:43:48 +0100 Subject: [PATCH] l2tp: make session IDR and tunnel session list coherent Modify l2tp_session_register and l2tp_session_unhash so that the session IDR and tunnel session lists remain coherent. To do so, hold the session IDR lock and the tunnel's session list lock when making any changes to either list. Without this change, a rare race condition could hit the WARN_ON_ONCE in l2tp_session_unhash if a thread replaced the IDR entry while another thread was registering the same ID. [ 7126.151795][T17511] WARNING: CPU: 3 PID: 17511 at net/l2tp/l2tp_core.c:1282 l2tp_session_delete.part.0+0x87e/0xbc0 [ 7126.163754][T17511] ? show_regs+0x93/0xa0 [ 7126.164157][T17511] ? __warn+0xe5/0x3c0 [ 7126.164536][T17511] ? l2tp_session_delete.part.0+0x87e/0xbc0 [ 7126.165070][T17511] ? report_bug+0x2e1/0x500 [ 7126.165486][T17511] ? l2tp_session_delete.part.0+0x87e/0xbc0 [ 7126.166013][T17511] ? handle_bug+0x99/0x130 [ 7126.166428][T17511] ? exc_invalid_op+0x35/0x80 [ 7126.166890][T17511] ? asm_exc_invalid_op+0x1a/0x20 [ 7126.167372][T17511] ? l2tp_session_delete.part.0+0x87d/0xbc0 [ 7126.167900][T17511] ? l2tp_session_delete.part.0+0x87e/0xbc0 [ 7126.168429][T17511] ? __local_bh_enable_ip+0xa4/0x120 [ 7126.168917][T17511] l2tp_session_delete+0x40/0x50 [ 7126.169369][T17511] pppol2tp_release+0x1a1/0x3f0 [ 7126.169817][T17511] __sock_release+0xb3/0x270 [ 7126.170247][T17511] ? __pfx_sock_close+0x10/0x10 [ 7126.170697][T17511] sock_close+0x1c/0x30 [ 7126.171087][T17511] __fput+0x40b/0xb90 [ 7126.171470][T17511] task_work_run+0x16c/0x260 [ 7126.171897][T17511] ? __pfx_task_work_run+0x10/0x10 [ 7126.172362][T17511] ? srso_alias_return_thunk+0x5/0xfbef5 [ 7126.172863][T17511] ? do_raw_spin_unlock+0x174/0x230 [ 7126.173348][T17511] do_exit+0xaae/0x2b40 [ 7126.173730][T17511] ? srso_alias_return_thunk+0x5/0xfbef5 [ 7126.174235][T17511] ? __pfx_lock_release+0x10/0x10 [ 7126.174690][T17511] ? srso_alias_return_thunk+0x5/0xfbef5 [ 7126.175190][T17511] ? do_raw_spin_lock+0x12c/0x2b0 [ 7126.175650][T17511] ? __pfx_do_exit+0x10/0x10 [ 7126.176072][T17511] ? _raw_spin_unlock_irq+0x23/0x50 [ 7126.176543][T17511] do_group_exit+0xd3/0x2a0 [ 7126.176990][T17511] __x64_sys_exit_group+0x3e/0x50 [ 7126.177456][T17511] x64_sys_call+0x1821/0x1830 [ 7126.177895][T17511] do_syscall_64+0xcb/0x250 [ 7126.178317][T17511] entry_SYSCALL_64_after_hwframe+0x77/0x7f Fixes: aa5e17e1f5ec ("l2tp: store l2tpv3 sessions in per-net IDR") Signed-off-by: James Chapman Signed-off-by: Tom Parkin Reviewed-by: Simon Horman Link: https://patch.msgid.link/20240718134348.289865-1-jchapman@katalix.com Signed-off-by: Paolo Abeni --- net/l2tp/l2tp_core.c | 32 ++++++++++++++------------------ 1 file changed, 14 insertions(+), 18 deletions(-) diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index 1c1decce7f06..c80ab3f26084 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -441,14 +441,15 @@ int l2tp_session_register(struct l2tp_session *session, int err; spin_lock_bh(&tunnel->list_lock); + spin_lock_bh(&pn->l2tp_session_idr_lock); + if (!tunnel->acpt_newsess) { err = -ENODEV; - goto err_tlock; + goto out; } if (tunnel->version == L2TP_HDR_VER_3) { session_key = session->session_id; - spin_lock_bh(&pn->l2tp_session_idr_lock); err = idr_alloc_u32(&pn->l2tp_v3_session_idr, NULL, &session_key, session_key, GFP_ATOMIC); /* IP encap expects session IDs to be globally unique, while @@ -462,43 +463,36 @@ int l2tp_session_register(struct l2tp_session *session, err = l2tp_session_collision_add(pn, session, other_session); } - spin_unlock_bh(&pn->l2tp_session_idr_lock); } else { session_key = l2tp_v2_session_key(tunnel->tunnel_id, session->session_id); - spin_lock_bh(&pn->l2tp_session_idr_lock); err = idr_alloc_u32(&pn->l2tp_v2_session_idr, NULL, &session_key, session_key, GFP_ATOMIC); - spin_unlock_bh(&pn->l2tp_session_idr_lock); } if (err) { if (err == -ENOSPC) err = -EEXIST; - goto err_tlock; + goto out; } l2tp_tunnel_inc_refcount(tunnel); - list_add(&session->list, &tunnel->session_list); - spin_unlock_bh(&tunnel->list_lock); - spin_lock_bh(&pn->l2tp_session_idr_lock); if (tunnel->version == L2TP_HDR_VER_3) { if (!other_session) idr_replace(&pn->l2tp_v3_session_idr, session, session_key); } else { idr_replace(&pn->l2tp_v2_session_idr, session, session_key); } - spin_unlock_bh(&pn->l2tp_session_idr_lock); - - trace_register_session(session); - return 0; - -err_tlock: +out: + spin_unlock_bh(&pn->l2tp_session_idr_lock); spin_unlock_bh(&tunnel->list_lock); + if (!err) + trace_register_session(session); + return err; } EXPORT_SYMBOL_GPL(l2tp_session_register); @@ -1260,13 +1254,13 @@ static void l2tp_session_unhash(struct l2tp_session *session) struct l2tp_net *pn = l2tp_pernet(tunnel->l2tp_net); struct l2tp_session *removed = session; - /* Remove from the per-tunnel list */ spin_lock_bh(&tunnel->list_lock); + spin_lock_bh(&pn->l2tp_session_idr_lock); + + /* Remove from the per-tunnel list */ list_del_init(&session->list); - spin_unlock_bh(&tunnel->list_lock); /* Remove from per-net IDR */ - spin_lock_bh(&pn->l2tp_session_idr_lock); if (tunnel->version == L2TP_HDR_VER_3) { if (hash_hashed(&session->hlist)) l2tp_session_collision_del(pn, session); @@ -1280,7 +1274,9 @@ static void l2tp_session_unhash(struct l2tp_session *session) session_key); } WARN_ON_ONCE(removed && removed != session); + spin_unlock_bh(&pn->l2tp_session_idr_lock); + spin_unlock_bh(&tunnel->list_lock); synchronize_rcu(); } -- 2.49.0