[Devel] [PATCH RH8 v2 2/2] drivers/connector: fix nullptr dereference ve->ve_ns->pid_ns

Andrey Zhadchenko andrey.zhadchenko at virtuozzo.com
Fri Jul 9 02:19:52 MSK 2021


cn_proc_ack incorrectly assumes that ve->ve_ns is not NULL. Check it.
Also add rcu_dereference since ve->ve_ns is rcu-protected.
For various fill callbacks we can omit rcu_read_lock and rcu_dereference
since ve_ns can only be destroyed after cn_fini_ve, which unregisters
connector and frees its data.

Example of crash when someone tries to register to connector with
ve_ns == NULL

[   52.805823] BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
[   52.807174] PGD 0 P4D 0
[   52.807548] Oops: 0000 [#1] SMP PTI
[   52.808060] CPU: 0 PID: 311 Comm: a.out ve: 1 Not tainted 4.18.0.ovz.custom #79 custom
[   52.809192] Hardware name: Virtuozzo KVM, BIOS 1.11.0-2.vz7.2 04/01/2014
[   52.810183] RIP: 0010:cn_proc_mcast_ctl+0x73/0x1a0
[   52.810994] Code: 41 5c 41 5d c3 48 89 fb 49 89 f4 4c 8b ad c0 08 00 00 e8 80 f6 95 ff 84 c0 74 cb 48 89 ef e8 f4 a5 8f ff 49 8b 95 98 01 00 00 <46
[   52.813662] RSP: 0018:ffffaadb003cbca0 EFLAGS: 00010206
[   52.814418] RAX: ffffffff980507a0 RBX: ffff8b99bb376a10 RCX: 0000000000000028
[   52.815448] RDX: 0000000000000000 RSI: ffff8b99b34c9628 RDI: ffff8b99bb300000
[   52.816509] RBP: ffff8b99bb300000 R08: ffffffff98225f80 R09: 0000000000000000
[   52.817645] R10: 0000000000000000 R11: 0000000000000028 R12: ffff8b99b34c9628
[   52.818664] R13: ffff8b99bb23b4d0 R14: ffff8b99b34c9628 R15: ffffaadb003cbe28
[   52.819716] FS:  00007f1555cc4540(0000) GS:ffff8b99bea00000(0000) knlGS:0000000000000000
[   52.820922] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   52.821746] CR2: 0000000000000020 CR3: 000000003d2d8000 CR4: 00000000000006f0
[   52.822767] Call Trace:
[   52.823183]  ? _cond_resched+0x15/0x30
[   52.823809]  ? __kmalloc_node_track_caller+0x1cb/0x280
[   52.824554]  ? __alloc_skb+0x82/0x1c0
[   52.825097]  ? __netlink_lookup+0xe6/0x150
[   52.825689]  cn_rx_skb+0xe1/0x120
[   52.826174]  netlink_unicast+0x21d/0x260
[   52.826739]  netlink_sendmsg+0x22e/0x400
[   52.827308]  sock_sendmsg+0x4c/0x50
[   52.827815]  __sys_sendto+0xee/0x160
[   52.828337]  ? __sys_bind+0xd2/0xf0
[   52.828845]  ? handle_mm_fault+0xc2/0x1d0
[   52.829428]  ? __do_page_fault+0x23a/0x4f0
[   52.830020]  __x64_sys_sendto+0x24/0x30
[   52.830576]  do_syscall_64+0x5b/0x1d0
[   52.831110]  entry_SYSCALL_64_after_hwframe+0x65/0xca
[   52.831836] RIP: 0033:0x7f1555bfd20c
[   52.832358] Code: 89 02 48 c7 c0 ff ff ff ff eb b8 0f 1f 00 41 89 ca 64 8b 04 25 18 00 00 00 85 c0 75 19 45 31 c9 45 31 c0 b8 2c 00 00 00 0f 05 <40
[   52.835010] RSP: 002b:00007fffc61bb878 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
[   52.836098] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f1555bfd20c
[   52.837115] RDX: 0000000000000028 RSI: 00007fffc61bb890 RDI: 0000000000000003
[   52.838137] RBP: 00007fffc61bb8c0 R08: 0000000000000000 R09: 0000000000000000
[   52.839158] R10: 0000000000000000 R11: 0000000000000246 R12: 00005630710cd120
[   52.840176] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[   52.841196] Modules linked in:
[   52.841639] Features: eBPF/cgroup
[   52.842120] CR2: 0000000000000020
[   52.842645] ---[ end trace 4508d0fc7c54945c ]---
[   52.843323] RIP: 0010:cn_proc_mcast_ctl+0x73/0x1a0
[   52.844018] Code: 41 5c 41 5d c3 48 89 fb 49 89 f4 4c 8b ad c0 08 00 00 e8 80 f6 95 ff 84 c0 74 cb 48 89 ef e8 f4 a5 8f ff 49 8b 95 98 01 00 00 <46
[   52.846714] RSP: 0018:ffffaadb003cbca0 EFLAGS: 00010206
[   52.847481] RAX: ffffffff980507a0 RBX: ffff8b99bb376a10 RCX: 0000000000000028
[   52.848507] RDX: 0000000000000000 RSI: ffff8b99b34c9628 RDI: ffff8b99bb300000
[   52.849533] RBP: ffff8b99bb300000 R08: ffffffff98225f80 R09: 0000000000000000
[   52.850561] R10: 0000000000000000 R11: 0000000000000028 R12: ffff8b99b34c9628
[   52.851588] R13: ffff8b99bb23b4d0 R14: ffff8b99b34c9628 R15: ffffaadb003cbe28
[   52.852616] FS:  00007f1555cc4540(0000) GS:ffff8b99bea00000(0000) knlGS:0000000000000000
[   52.853778] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   52.854649] CR2: 0000000000000020 CR3: 000000003d2d8000 CR4: 00000000000006f0
[   52.855681] Kernel panic - not syncing: Fatal exception
[   52.856567] Kernel Offset: 0x15800000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
[   52.858158] ---[ end Kernel panic - not syncing: Fatal exception ]---

https://jira.sw.ru/browse/PSBM-130894
Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
---
v2: remove a lot of excessive rcu_dereference in connector

 drivers/connector/cn_proc.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
index 61fd165..ab95de5 100644
--- a/drivers/connector/cn_proc.c
+++ b/drivers/connector/cn_proc.c
@@ -342,6 +342,7 @@ static void cn_proc_mcast_ctl(struct cn_msg *msg,
 {
 	enum proc_cn_mcast_op *mc_op = NULL;
 	struct ve_struct *ve = get_exec_env();
+	struct nsproxy *ve_ns;
 	int err = 0;
 
 	if (msg->len != sizeof(*mc_op))
@@ -352,9 +353,14 @@ static void cn_proc_mcast_ctl(struct cn_msg *msg,
 	 * and user namespaces so ignore requestors from
 	 * other namespaces.
 	 */
-	if (!current_user_ns_initial() ||
-	    (task_active_pid_ns(current) != ve->ve_ns->pid_ns_for_children))
+	rcu_read_lock();
+	ve_ns = rcu_dereference(ve->ve_ns);
+	if (!current_user_ns_initial() || !ve_ns ||
+	    (task_active_pid_ns(current) != ve_ns->pid_ns_for_children)) {
+		rcu_read_unlock();
 		return;
+	}
+	rcu_read_unlock();
 
 	/* Can only change if privileged. */
 	if (!__netlink_ns_capable(nsp, ve_init_user_ns(), CAP_NET_ADMIN)) {
-- 
1.8.3.1



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