From: Theodore Ts'o <tytso@mit.edu>
To: Junho Ryu <jayr@google.com>
Cc: linux-ext4@vger.kernel.org
Subject: Re: [PATCH] ext4: fix use-after-free in ext4_mb_new_blocks
Date: Tue, 3 Dec 2013 18:10:52 -0500 [thread overview]
Message-ID: <20131203231052.GC24466@thunk.org> (raw)
In-Reply-To: <1384991735-18118-1-git-send-email-jayr@google.com>
On Wed, Nov 20, 2013 at 03:55:35PM -0800, Junho Ryu wrote:
> ext4_mb_put_pa should hold pa->pa_lock before accessing pa->pa_count.
> While ext4_mb_use_preallocated checks pa->pa_deleted first and then
> increments pa->count later, ext4_mb_put_pa decrements pa->pa_count
> before holding pa->pa_lock and then sets pa->pa_deleted.
>
> * Free sequence
> ext4_mb_put_pa (1): atomic_dec_and_test pa->pa_count
> ext4_mb_put_pa (2): lock pa->pa_lock
> ext4_mb_put_pa (3): check pa->pa_deleted
> ext4_mb_put_pa (4): set pa->pa_deleted=1
> ext4_mb_put_pa (5): unlock pa->pa_lock
> ext4_mb_put_pa (6): remove pa from a list
> ext4_mb_pa_callback: free pa
>
> * Use sequence
> ext4_mb_use_preallocated (1): iterate over preallocation
> ext4_mb_use_preallocated (2): lock pa->pa_lock
> ext4_mb_use_preallocated (3): check pa->pa_deleted
> ext4_mb_use_preallocated (4): increase pa->pa_count
> ext4_mb_use_preallocated (5): unlock pa->pa_lock
> ext4_mb_release_context: access pa
>
> * Use-after-free sequence
> [initial status] <pa->pa_deleted = 0, pa_count = 1>
> ext4_mb_use_preallocated (1): iterate over preallocation
> ext4_mb_use_preallocated (2): lock pa->pa_lock
> ext4_mb_use_preallocated (3): check pa->pa_deleted
> ext4_mb_put_pa (1): atomic_dec_and_test pa->pa_count
> [pa_count decremented] <pa->pa_deleted = 0, pa_count = 0>
> ext4_mb_use_preallocated (4): increase pa->pa_count
> [pa_count incremented] <pa->pa_deleted = 0, pa_count = 1>
> ext4_mb_use_preallocated (5): unlock pa->pa_lock
> ext4_mb_put_pa (2): lock pa->pa_lock
> ext4_mb_put_pa (3): check pa->pa_deleted
> ext4_mb_put_pa (4): set pa->pa_deleted=1
> [race condition!] <pa->pa_deleted = 1, pa_count = 1>
> ext4_mb_put_pa (5): unlock pa->pa_lock
> ext4_mb_put_pa (6): remove pa from a list
> ext4_mb_pa_callback: free pa
> ext4_mb_release_context: access pa
>
> AddressSanitizer has detected use-after-free in ext4_mb_new_blocks
> Bug report: http://goo.gl/rG1On3
>
> Signed-off-by: Junho Ryu <jayr@google.com>
Thanks, applied.
- Ted
prev parent reply other threads:[~2013-12-03 23:10 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-11-20 23:55 [PATCH] ext4: fix use-after-free in ext4_mb_new_blocks Junho Ryu
2013-12-03 23:10 ` Theodore Ts'o [this message]
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