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exit: call disassociate_ctty() before exit_task_namespaces()

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Commit 8aac62706a ("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: ppp_register_channel+0x13/0x20 [ppp_generic]
    Call Trace:
      ppp_asynctty_open+0x12b/0x170 [ppp_async]
      tty_ldisc_open.isra.2+0x27/0x60
      tty_ldisc_hangup+0x1e3/0x220
      __tty_hangup+0x2c4/0x440
      disassociate_ctty+0x61/0x270
      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]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Oleg Nesterov 2014-04-07 15:38:29 -07:00 • committed by Linus Torvalds
commit c39df5fa37
1 changed files with 2 additions and 4 deletions
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6
kernel/exit.c
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@ -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
*/