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List: linux-unionfs
Subject: Re: [PATCH 2/2] ovl: fix UAF for ovl_aio_req
From: yangerkun <yangerkun () huawei ! com>
Date: 2021-11-01 10:52:52
Message-ID: d494e28c-0167-6e67-2028-0a1c65df77d1 () huawei ! com
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On 2021/11/1 17:15, Miklos Szeredi wrote:
> On Mon, 1 Nov 2021 at 05:02, yangerkun <yangerkun@huawei.com> wrote:
>>
>>
>>
>> On 2021/10/29 19:40, Miklos Szeredi wrote:
>>> On Thu, Oct 28, 2021 at 08:41:28PM +0800, yangerkun wrote:
>>>>
>>>>
>>>> 在 2021/10/18 22:26, yangerkun 写道:
>>>>>
>>>>>
>>>>> 在 2021/10/8 23:13, Miklos Szeredi 写道:
>>>>>> On Thu, 30 Sept 2021 at 05:12, yangerkun <yangerkun@huawei.com> wrote:
>>>>>>>
>>>>>>> Our testcase trigger follow UAF:
>>>>>>>
>>>>>>> [ 153.939147]
>>>>>>> ==================================================================
>>>>>>> [ 153.942199] BUG: KASAN: use-after-free in
>>>>>>> ext4_dio_read_iter+0xcc/0x1a0
>>>>>>> [ 153.943331] Read of size 8 at addr ffff88803b7f1500 by task
>>>>>>> fsstress/726
>>>>>>> [ 153.948182] Call Trace:
>>>>>>> [ 153.948628] ? dump_stack_lvl+0x73/0x9f
>>>>>>> [ 153.950255] ? ext4_dio_read_iter+0xcc/0x1a0
>>>>>>> [ 153.950972] ? ext4_dio_read_iter+0xcc/0x1a0
>>>>>>> [ 153.951693] ? kasan_report.cold+0x81/0x165
>>>>>>> [ 153.952429] ? ext4_dio_read_iter+0xcc/0x1a0
>>>>>>> [ 153.953190] ? __asan_load8+0x74/0x110
>>>>>>> [ 153.953856] ? ext4_dio_read_iter+0xcc/0x1a0
>>>>>>> [ 153.954612] ? ext4_file_read_iter+0x1df/0x2a0
>>>>>>> [ 153.955394] ? ext4_dio_read_iter+0x1a0/0x1a0
>>>>>>> [ 153.956159] ? vfs_iocb_iter_read+0xd5/0x330
>>>>>>> [ 153.956916] ? ovl_read_iter+0x15f/0x270
>>>>>>> [ 153.957605] ? ovl_aio_cleanup_handler+0x2a0/0x2a0
>>>>>>> [ 153.958436] ? aio_setup_rw+0xbf/0xe0
>>>>>>> [ 153.959101] ? aio_read+0x190/0x2d0
>>>>>>> [ 153.959750] ? aio_write+0x3e0/0x3e0
>>>>>>> [ 153.960404] ? __kasan_check_read+0x1d/0x30
>>>>>>> [ 153.961167] ? ext4_file_getattr+0x116/0x1b0
>>>>>>> [ 153.961978] ? __put_user_ns+0x40/0x40
>>>>>>> [ 153.962714] ? kasan_poison+0x40/0x90
>>>>>>> [ 153.963384] ? set_alloc_info+0x46/0x70
>>>>>>> [ 153.964102] ? __kasan_check_write+0x20/0x30
>>>>>>> [ 153.964856] ? __fget_files+0x106/0x180
>>>>>>> [ 153.965571] ? io_submit_one+0xaa7/0x1480
>>>>>>> [ 153.966325] ? aio_poll_complete_work+0x590/0x590
>>>>>>> [ 153.967713] ? ioctl_file_clone+0x110/0x110
>>>>>>> [ 153.969008] ? vfs_getattr_nosec+0x14a/0x190
>>>>>>> [ 153.970539] ? __do_sys_newfstat+0xd6/0xf0
>>>>>>> [ 153.971713] ? __ia32_compat_sys_newfstat+0x40/0x40
>>>>>>> [ 153.973005] ? __x64_sys_io_submit+0x125/0x3b0
>>>>>>> [ 153.974282] ? __ia32_sys_io_submit+0x390/0x390
>>>>>>> [ 153.975575] ? __kasan_check_read+0x1d/0x30
>>>>>>> [ 153.976749] ? do_syscall_64+0x35/0x80
>>>>>>> [ 153.978034] ? entry_SYSCALL_64_after_hwframe+0x44/0xae
>>>>>>> [ 153.979436]
>>>>>>> [ 153.979738] Allocated by task 726:
>>>>>>> [ 153.980352] kasan_save_stack+0x23/0x60
>>>>>>> [ 153.981054] set_alloc_info+0x46/0x70
>>>>>>> [ 153.981745] __kasan_slab_alloc+0x4c/0x90
>>>>>>> [ 153.982492] kmem_cache_alloc+0x153/0x750
>>>>>>> [ 153.983953] ovl_read_iter+0x13b/0x270
>>>>>>> [ 153.984689] aio_read+0x190/0x2d0
>>>>>>> [ 153.985332] io_submit_one+0xaa7/0x1480
>>>>>>> [ 153.986060] __x64_sys_io_submit+0x125/0x3b0
>>>>>>> [ 153.986878] do_syscall_64+0x35/0x80
>>>>>>> [ 153.987590] entry_SYSCALL_64_after_hwframe+0x44/0xae
>>>>>>> [ 153.988516]
>>>>>>> [ 153.988824] Freed by task 750:
>>>>>>> [ 153.989417] kasan_save_stack+0x23/0x60
>>>>>>> [ 153.990140] kasan_set_track+0x24/0x40
>>>>>>> [ 153.990871] kasan_set_free_info+0x30/0x60
>>>>>>> [ 153.991639] __kasan_slab_free+0x137/0x210
>>>>>>> [ 153.992390] kmem_cache_free+0xf8/0x590
>>>>>>> [ 153.993303] ovl_aio_cleanup_handler+0x1ae/0x2a0
>>>>>>> [ 153.994205] ovl_aio_rw_complete+0x31/0x60
>>>>>>> [ 153.995043] iomap_dio_complete_work+0x4b/0x60
>>>>>>> [ 153.995898] iomap_dio_bio_end_io+0x23d/0x270
>>>>>>> [ 153.996742] bio_endio+0x40d/0x440
>>>>>>> [ 153.997376] blk_update_request+0x38f/0x820
>>>>>>> [ 153.998160] scsi_end_request+0x56/0x320
>>>>>>> [ 153.998872] scsi_io_completion+0x10a/0xb60
>>>>>>> [ 153.999655] scsi_finish_command+0x194/0x2b0
>>>>>>> [ 154.000464] scsi_complete+0xd7/0x1f0
>>>>>>> [ 154.001184] blk_complete_reqs+0x92/0xb0
>>>>>>> [ 154.001930] blk_done_softirq+0x29/0x40
>>>>>>> [ 154.002696] __do_softirq+0x133/0x57f
>>>>>>>
>>>>>>> ext4_dio_read_iter
>>>>>>> ret = iomap_dio_rw(iocb, to, &ext4_iomap_ops, NULL, 0)
>>>>>>> file_accessed(iocb->ki_filp) <== this trigger UAF
>>>>>>>
>>>>>>> Ret can be -EIOCBQUEUED which means we will not wait for io
>>>>>>> completion in
>>>>>>> iomap_dio_rw. So the release for ovl_aio_req will be done when io
>>>>>>> completion routine call ovl_aio_rw_complete(or ovl_aio_cleanup_handler
>>>>>>> in ovl_read_iter will do this). But once io finish soon, we may already
>>>>>>> release ovl_aio_req before we call file_access in ext4_dio_read_iter.
>>>>>>> This can trigger the upper UAF.
>>>>>>>
>>>>>>> Fix it by introduce refcount in ovl_aio_req like what aio_kiocb has did.
>>>>>>
>>>>>> Looks good at a glance. Will review more fully.
>>>>>
>>>>> Hi,
>>>>>
>>>>> Any comments for this patch? :)
>>>
>>> Thanks for the patch. I found one issue: the fdput() needs to be moved to the
>>> destruction as well, since the iocb->ki_filp reference comes from aio_req->fd.
>>
>> Hi, it seems we will only use aio_req->iocb in ovl_aio_cleanup_handler
>> before we call fdput(aio_req->fd):
>
> Correct. However I'm taking about this call:
> file_accessed(iocb->ki_filp). If the fdput() is done from
> ovl_aio_cleanup_handler() which is called from ->ki_complete() then
> this would put the file, agains resulting in a UAF, only inside
> file_accessed() this time. The reason why you weren't seeing this,
> is probably that most of the time aio_req->fd is from
> file->private_data, which is the real file obtained at open time, and
> which isn't actually closed at fdput() (flags == 0).
Thanks for your analysis. Got it now!
>
>>
>> static void ovl_aio_cleanup_handler(struct ovl_aio_req *aio_req)
>> {
>> struct kiocb *iocb = &aio_req->iocb;
>> struct kiocb *orig_iocb = aio_req->orig_iocb;
>>
>> if (iocb->ki_flags & IOCB_WRITE) {
>> struct inode *inode = file_inode(orig_iocb->ki_filp);
>>
>> /* Actually acquired in ovl_write_iter() */
>> __sb_writers_acquired(file_inode(iocb->ki_filp)->i_sb,
>> SB_FREEZE_WRITE);
>> file_end_write(iocb->ki_filp);
>> <=== use iocb
>> ovl_copyattr(ovl_inode_real(inode), inode);
>> }
>>
>> orig_iocb->ki_pos = iocb->ki_pos;
>> fdput(aio_req->fd); <=== release aio_req->fd
>> kmem_cache_free(ovl_aio_request_cachep, aio_req);
>> }
>>
>> So call fdput(aio_req->fd) in ovl_aio_cleanup_handler or ovl_aio_put
>> seems all ok for me.
>>
>>>
>>> Other than that, it looks good.
>>>
>>> Minor things:
>>>
>>> - instead of setting refcount to 1 and incrementing it, just initialize it to 2
>>>
>>> - code deduplication can come after the fix (if at all), this helps backporting
>>
>> Agree.
>>
>>>
>>> - cleaned up header comment
>>>
>>> Here's the updated patch, can you please verify that I didn't break anything?
>>
>> Thanks! This patch can help pass the test!
>
> Great, thanks.
>
> Miklos
> .
>
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