Messages in this thread | | | Date | Sun, 28 Jun 2015 15:21:19 -0400 | From | Peter Hurley <> | Subject | Re: [PATCH v2 1/2] tty: add missing rcu_read_lock for task_pgrp |
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On 06/28/2015 01:20 PM, Patrick Donnelly wrote: > 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.
I suppose it can't hurt; please add similar logic to job_control() in drivers/tty/n_tty.c which handles the corresponding SIGTTIN signal conditions.
Regards, Peter Hurley
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