On Sun, Jun 28, 2015 at 11:23 AM, Peter Hurley <pe...@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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
