From: Oleg Nesterov <[email protected]>
Subject: exit: call disassociate_ctty() before exit_task_namespaces()
8aac62706ada ("move exit_task_namespaces() outside of exit_notify()")
breaks pppd and the exiting service crashes the kernel:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000028
IP: [<ffffffffa06985a3>] ppp_register_channel+0x13/0x20 [ppp_generic]
...
Call Trace:
[<ffffffffa06ab2ab>] ? ppp_asynctty_open+0x12b/0x170 [ppp_async]
[<ffffffff812ec907>] ? tty_ldisc_open.isra.2+0x27/0x60
[<ffffffff812ed1d3>] ? tty_ldisc_hangup+0x1e3/0x220
[<ffffffff812e4614>] ? __tty_hangup+0x2c4/0x440
[<ffffffff812e56a1>] ? disassociate_ctty+0x61/0x270
[<ffffffff810483c2>] ? do_exit+0x7f2/0xa50
ppp_register_channel() needs ->net_ns and current->nsproxy == NULL.
Move disassociate_ctty() before exit_task_namespaces(), it doesn't make
sense to delay it after perf_event_exit_task() or cgroup_exit().
This also allows to use task_work_add() inside the (nontrivial) code
paths in disassociate_ctty().
Investigated by Peter Hurley.
Signed-off-by: Oleg Nesterov <[email protected]>
Reported-by: Sree Harsha Totakura <[email protected]>
Cc: Peter Hurley <[email protected]>
Cc: Sree Harsha Totakura <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: Jeff Dike <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Andrey Vagin <[email protected]>
Cc: Al Viro <[email protected]>
Cc: <[email protected]> [v3.10+]
Signed-off-by: Andrew Morton <[email protected]>
---
kernel/exit.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff -puN kernel/exit.c~exit-call-disassociate_ctty-before-exit_task_namespaces
kernel/exit.c
--- a/kernel/exit.c~exit-call-disassociate_ctty-before-exit_task_namespaces
+++ a/kernel/exit.c
@@ -784,6 +784,8 @@ void do_exit(long code)
exit_shm(tsk);
exit_files(tsk);
exit_fs(tsk);
+ if (group_dead)
+ disassociate_ctty(1);
exit_task_namespaces(tsk);
exit_task_work(tsk);
check_stack_usage();
@@ -799,13 +801,9 @@ void do_exit(long code)
cgroup_exit(tsk);
- if (group_dead)
- disassociate_ctty(1);
-
module_put(task_thread_info(tsk)->exec_domain->module);
proc_exit_connector(tsk);
-
/*
* FIXME: do that only when needed, using sched_exit tracepoint
*/
_
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