Messages in this thread | | | Date | Sun, 28 Jun 2015 13:20:34 -0400 | Subject | Re: [PATCH v2 1/2] tty: add missing rcu_read_lock for task_pgrp | From | Patrick Donnelly <> |
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On Sun, Jun 28, 2015 at 11:23 AM, Peter Hurley <peter@hurleysoftware.com> wrote: > On 06/27/2015 08:51 PM, Patrick Donnelly wrote: >> task_pgrp requires an rcu or tasklist lock to be obtained if the returned pid >> is to be dereferenced, which kill_pgrp does. Obtain an RCU lock for the >> duration of use. > > kill_pgrp() obtains tasklist_lock, so I don't see an unsafe deref.
I see a race between looking up the pgrp via task_pgrp and passing it to kill_pgrp. The pgrp struct pid may be freed via setpgid/setsid, as mentioned in the comment for task_pgrp:
* Without tasklist or rcu lock it is not safe to dereference * the result of task_pgrp/task_session even if task == current, * we can race with another thread doing sys_setsid/sys_setpgid.
Getting the lock after the lookup is getting the lock too late. I could be wrong though as I'm no expert on locking in Linux.
-- Patrick Donnelly
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