Re: include/linux/cgroup.h:566 suspicious rcu_dereference_check() usage!

[Sergey Senozhatsky <sergey.senozhatsky@gmail.com>]

On (10/09/12 20:25), Paul E. McKenney wrote:
> 
> Looks sane to me!  Dropping my patch.
> 
> 							Thanx, Paul
>

Thanks a lot, Paul. I will resend with proper subject, so it'll be more visible in the list.

	-ss

 
> > ----------------------------------------------------------------------------
> > 
> > Commit ad676077
> >  | Author: Aristeu Rozanski <aris@redhat.com>
> >  | Date:   Thu Oct 4 17:15:17 2012 -0700
> >  |   device_cgroup: convert device_cgroup internally to policy + exceptions
> > 
> > moved RCU read-side protection from devcgroup_inode_mknod(), which, however is required
> > by task_devcgroup(). Patch also add RCU read-side protection to __devcgroup_inode_permission()
> > function, introduced in commit ad676077.
> > 
> > [    0.946303] include/linux/cgroup.h:566 suspicious rcu_dereference_check() usage!
> > [    0.946511] 
> > [    0.946606] 2 locks held by kdevtmpfs/28:
> > [    0.946684]  #0:  (sb_writers){.+.+.+}, at: [<ffffffff81144bcb>] mnt_want_write+0x24/0x4b
> > [    0.947083]  #1:  (&sb->s_type->i_mutex_key#3/1){+.+.+.}, at: [<ffffffff81133d04>] kern_path_create+0x83/0x144
> > [    0.947598] 
> > [    0.947787] Call Trace:
> > [    0.947868]  [<ffffffff81089644>] lockdep_rcu_suspicious+0x109/0x112
> > [    0.947958]  [<ffffffff81258fa0>] devcgroup_inode_mknod+0x9e/0xee
> > [    0.948043]  [<ffffffff81132ee7>] vfs_mknod+0x8a/0xed
> > [    0.948129]  [<ffffffff813b98af>] handle_create.isra.2+0x144/0x1b5
> > [    0.948214]  [<ffffffff813b99bf>] ? devtmpfsd+0x9f/0x138
> > [    0.948298]  [<ffffffff81295d5c>] ? do_raw_spin_lock+0x67/0xde
> > [    0.948384]  [<ffffffff81295e92>] ? do_raw_spin_unlock+0x8f/0x98
> > [    0.948469]  [<ffffffff813b9920>] ? handle_create.isra.2+0x1b5/0x1b5
> > [    0.948554]  [<ffffffff813b9a04>] devtmpfsd+0xe4/0x138
> > [    0.948638]  [<ffffffff813b9920>] ? handle_create.isra.2+0x1b5/0x1b5
> > [    0.948724]  [<ffffffff810582b6>] kthread+0xd5/0xdd
> > [    0.948814]  [<ffffffff814db664>] kernel_thread_helper+0x4/0x10
> > [    0.948900]  [<ffffffff814d2973>] ? retint_restore_args+0x13/0x13
> > [    0.948985]  [<ffffffff810581e1>] ? __init_kthread_worker+0x5a/0x5a
> > [    0.949069]  [<ffffffff814db660>] ? gs_change+0x13/0x13
> > 
> > 
> > devcgroup_inode_mknod() part submitted by Paul E. McKenney.
> > 
> > 
> > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> > 
> > ---
> > 
> >  security/device_cgroup.c | 21 +++++++++++++++++----
> >  1 file changed, 17 insertions(+), 4 deletions(-)
> > 
> > diff --git a/security/device_cgroup.c b/security/device_cgroup.c
> > index 44dfc41..043eb00 100644
> > --- a/security/device_cgroup.c
> > +++ b/security/device_cgroup.c
> > @@ -558,7 +558,8 @@ static int __devcgroup_check_permission(struct dev_cgroup *dev_cgroup,
> > 
> >  int __devcgroup_inode_permission(struct inode *inode, int mask)
> >  {
> > -	struct dev_cgroup *dev_cgroup = task_devcgroup(current);
> > +	struct dev_cgroup *dev_cgroup;
> > +	int ret;
> >  	short type, access = 0;
> > 
> >  	if (S_ISBLK(inode->i_mode))
> > @@ -570,13 +571,20 @@ int __devcgroup_inode_permission(struct inode *inode, int mask)
> >  	if (mask & MAY_READ)
> >  		access |= ACC_READ;
> > 
> > -	return __devcgroup_check_permission(dev_cgroup, type, imajor(inode),
> > +	rcu_read_lock();
> > +
> > +	dev_cgroup = task_devcgroup(current);
> > +	ret = __devcgroup_check_permission(dev_cgroup, type, imajor(inode),
> >  					    iminor(inode), access);
> > +
> > +	rcu_read_unlock();
> > +	return ret;
> >  }
> > 
> >  int devcgroup_inode_mknod(int mode, dev_t dev)
> >  {
> > -	struct dev_cgroup *dev_cgroup = task_devcgroup(current);
> > +	struct dev_cgroup *dev_cgroup;
> > +	int ret;
> >  	short type;
> > 
> >  	if (!S_ISBLK(mode) && !S_ISCHR(mode))
> > @@ -587,7 +595,12 @@ int devcgroup_inode_mknod(int mode, dev_t dev)
> >  	else
> >  		type = DEV_CHAR;
> > 
> > -	return __devcgroup_check_permission(dev_cgroup, type, MAJOR(dev),
> > +	rcu_read_lock();
> > +
> > +	dev_cgroup = task_devcgroup(current);
> > +	ret = __devcgroup_check_permission(dev_cgroup, type, MAJOR(dev),
> >  					    MINOR(dev), ACC_MKNOD);
> > 
> > +	rcu_read_unlock();
> > +	return ret; 
> >  }
> > 
> > --
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