From: Greg KH <greg@kroah.com>
To: Chas Williams <3chas3@gmail.com>
Cc: stable@vger.kernel.org, David Howells <dhowells@redhat.com>
Subject: Re: [PATCH 4.1.y] KEYS: Fix crash when attempt to garbage collect an uninstantiated keyring
Date: Wed, 20 Jan 2016 08:45:31 -0800 [thread overview]
Message-ID: <20160120164531.GB28629@kroah.com> (raw)
In-Reply-To: <1449010000-1144-1-git-send-email-3chas3@gmail.com>
On Tue, Dec 01, 2015 at 05:46:40PM -0500, Chas Williams wrote:
> From: David Howells <dhowells@redhat.com>
>
> Commit f05819df10d7b09f6d1eb6f8534a8f68e5a4fe61 upstream.
>
> The following sequence of commands:
>
> i=`keyctl add user a a @s`
> keyctl request2 keyring foo bar @t
> keyctl unlink $i @s
>
> tries to invoke an upcall to instantiate a keyring if one doesn't already
> exist by that name within the user's keyring set. However, if the upcall
> fails, the code sets keyring->type_data.reject_error to -ENOKEY or some
> other error code. When the key is garbage collected, the key destroy
> function is called unconditionally and keyring_destroy() uses list_empty()
> on keyring->type_data.link - which is in a union with reject_error.
> Subsequently, the kernel tries to unlink the keyring from the keyring names
> list - which oopses like this:
>
> BUG: unable to handle kernel paging request at 00000000ffffff8a
> IP: [<ffffffff8126e051>] keyring_destroy+0x3d/0x88
> ...
> Workqueue: events key_garbage_collector
> ...
> RIP: 0010:[<ffffffff8126e051>] keyring_destroy+0x3d/0x88
> RSP: 0018:ffff88003e2f3d30 EFLAGS: 00010203
> RAX: 00000000ffffff82 RBX: ffff88003bf1a900 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: 000000003bfc6901 RDI: ffffffff81a73a40
> RBP: ffff88003e2f3d38 R08: 0000000000000152 R09: 0000000000000000
> R10: ffff88003e2f3c18 R11: 000000000000865b R12: ffff88003bf1a900
> R13: 0000000000000000 R14: ffff88003bf1a908 R15: ffff88003e2f4000
> ...
> CR2: 00000000ffffff8a CR3: 000000003e3ec000 CR4: 00000000000006f0
> ...
> Call Trace:
> [<ffffffff8126c756>] key_gc_unused_keys.constprop.1+0x5d/0x10f
> [<ffffffff8126ca71>] key_garbage_collector+0x1fa/0x351
> [<ffffffff8105ec9b>] process_one_work+0x28e/0x547
> [<ffffffff8105fd17>] worker_thread+0x26e/0x361
> [<ffffffff8105faa9>] ? rescuer_thread+0x2a8/0x2a8
> [<ffffffff810648ad>] kthread+0xf3/0xfb
> [<ffffffff810647ba>] ? kthread_create_on_node+0x1c2/0x1c2
> [<ffffffff815f2ccf>] ret_from_fork+0x3f/0x70
> [<ffffffff810647ba>] ? kthread_create_on_node+0x1c2/0x1c2
>
> Note the value in RAX. This is a 32-bit representation of -ENOKEY.
>
> The solution is to only call ->destroy() if the key was successfully
> instantiated.
>
> Fixes CVE-2015-7872.
>
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: David Howells <dhowells@redhat.com>
> Tested-by: Dmitry Vyukov <dvyukov@google.com>
> [3chas3@gmail.com: backported to 4.1 due to context changes]
I took an earlier keys patch as well, which didn't require this context
change, but thanks for the backport.
greg k-h
prev parent reply other threads:[~2016-01-20 16:45 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-01 22:46 [PATCH 4.1.y] KEYS: Fix crash when attempt to garbage collect an uninstantiated keyring Chas Williams
2016-01-20 16:45 ` Greg KH [this message]
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