linux-kernel - Re: [PATCH] tmpfs: security xattr setting on inode creation

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Message-ID: <CADjiTvCViw4tZ9HvH-s8a2_8uW82BwfXz3PLQmEEVAVC0PbDwg@mail.gmail.com>
Date:	Tue, 28 Feb 2012 07:51:26 +0200
From:	"Sakkinen, Jarkko" <jarkko.sakkinen@...el.com>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	"Ware, Ryan R" <ryan.r.ware@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	James Morris <jmorris@...ei.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH] tmpfs: security xattr setting on inode creation

On Tue, Feb 28, 2012 at 6:10 AM, Hugh Dickins <hughd@...gle.com> wrote:
> On Tue, 28 Feb 2012, Ware, Ryan R wrote:
>> On Tue, Feb 28, 2012 at 7:46 AM, Andrew Morton <akpm@...ux-foundation.org>wrote:
>> > On Fri, 24 Feb 2012 19:19:22 -0800 (PST)
>> > Hugh Dickins <hughd@...gle.com> wrote:
>> >...
>> > > +             if (!new_xattr->name) {
>> > > +                     kfree(new_xattr);
>> > > +                     return -ENOMEM;
>> > > +             }
>> > > +
>> > > +             memcpy(new_xattr->name, XATTR_SECURITY_PREFIX,
>> > > +                    XATTR_SECURITY_PREFIX_LEN);
>> > > +             memcpy(new_xattr->name + XATTR_SECURITY_PREFIX_LEN,
>> > > +                    xattr->name, len);
>> > > +
>> > > +             spin_lock(&info->lock);
>> > > +             list_add(&new_xattr->list, &info->xattr_list);
>> > > +             spin_unlock(&info->lock);
>> > > +     }
>> > > +
>> > > +     return 0;
>> > > +}
>> >
>> > So if there's a kmalloc failure partway through the array, we leave a
>> > partially xattrified inode in place.
>> >
>> > Are we sure this is OK?
>> >
>>
>> I'm guessing Jarkko can clean that up a bit.  It wouldn't be a good idea to
>> leave inaccurate data structures laying around during failure cases.
>
> Andrew raises a good concern, but Jarkko got it just right and no
> change is needed: any xattrs already allocated are properly linked
> on info->xattr_list, then when security_inode_init_security() fails
> (with an error other than EOPNOTSUPP) the failing inode is iput(),
> which ends up in shmem_evict_inode(), which kfree()s those xattrs
> (and their names) on info->xattr_list.

Yeah, that's how I understood it too. These the are places where
security_inode_init_security() is called:

- http://lxr.free-electrons.com/source/mm/shmem.c#L1459
- http://lxr.free-electrons.com/source/mm/shmem.c#L1590

>
> Hugh

/Jarkko
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