Messages in this thread | | | Date | Fri, 3 Jan 2014 12:51:51 +0000 | From | Chris Wilson <> | Subject | Re: [PATCH] drm/i915: Fix refcount leak and possible NULL pointerdereference. |
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On Fri, Jan 03, 2014 at 08:42:18PM +0900, Tetsuo Handa wrote: > Chris Wilson wrote: > > On Tue, Dec 24, 2013 at 08:50:23PM +0900, Tetsuo Handa wrote: > > > >From 482be6384379072eb4c0d45d0ab8a25df4f59ed7 Mon Sep 17 00:00:00 2001 > > > From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > > > Date: Tue, 24 Dec 2013 18:04:14 +0900 > > > Subject: [PATCH] drm/i915: Fix refcount leak and possible NULL pointer dereference. > > > > > > Since get_pid_task() grabs a reference on the task_struct, we have to drop the > > > refcount after reading that task's comm name. Also, directly reading like > > > get_pid_task()->comm can trigger an oops when get_pid_task() returned NULL. > > > > The second issue is moot as file itself cannot exist if the task_struct > > is NULL, and the task_struct cannot be destroyed until we finish the > > function. The simpler fix would appear to be s/get_pid_task/pid_task/ > > If I understand correctly, priv->pid = get_pid(task_pid(current)); in > drm_open_helper() grabs a reference on "struct pid" before adding to > &dev->filelist, and put_pid(file_priv->pid); in drm_release() releases that > reference after removing from &dev->filelist. > > So, you meant that mutex_lock_interruptible(&dev->struct_mutex); in > i915_gem_object_info() prevents drm_release() from calling put_pid() ?
Right, my understanding is that since we take the struct_mutex during release of the filp (and across this list walker) that is sufficient serialisation to prevent the task struct from disappearing from underneath us.
> Then, this file->pid in &dev->filelist keeps at least one reference. > OK. Updated patch follows.
Looks good to me, and the comment is great. -Chris
-- Chris Wilson, Intel Open Source Technology Centre
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