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Subject: Re: [PATCH] aio: take an extra file reference before call vfs_poll()
From:   Hou Tao <houtao1@huawei.com>
To:     <linux-fsdevel@vger.kernel.org>, <linux-aio@kvack.org>,
        Christoph Hellwig <hch@lst.de>
CC:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Benjamin LaHaise <bcrl@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
References: <20190225090332.88640-1-houtao1@huawei.com>
 <b9976295-0324-dd98-2546-c8de6ff70a43@huawei.com>
Message-ID: <978dc206-d28e-fb5d-e857-8d16e160a87c@huawei.com>
Date:   Tue, 5 Mar 2019 09:17:07 +0800
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ping ?

On 2019/3/1 18:09, Hou Tao wrote:
> ping ?
> 
> On 2019/2/25 17:03, Hou Tao wrote:
>> Taking an extra file reference before call vfs_poll(), else
>> the file may be released by aio_poll_wake() if an expected
>> event is triggered immediately (e.g., by the close of a
>> pair of pipes) after the return of vfs_poll(), and we may
>> hit a use-after-free splat as shown below:
>>
>>  BUG: KASAN: use-after-free in perf_trace_lock_acquire+0x3ab/0x570
>>  Read of size 8 at addr ffff888379bfd4b0 by task syz-executor.1/4953
>>
>>  CPU: 0 PID: 4953 Comm: syz-executor.1 Not tainted 4.19.24
>>  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1
>>  Call Trace:
>>   __dump_stack lib/dump_stack.c:77 [inline]
>>   dump_stack+0xca/0x13e lib/dump_stack.c:113
>>   print_address_description+0x79/0x330 mm/kasan/report.c:256
>>   kasan_report_error mm/kasan/report.c:354 [inline]
>>   kasan_report+0x18a/0x2e0 mm/kasan/report.c:412
>>   trace_event_get_offsets_lock_acquire include/trace/events/lock.h:13 [inline]
>>   perf_trace_lock_acquire+0x3ab/0x570 include/trace/events/lock.h:13
>>   trace_lock_acquire include/trace/events/lock.h:13 [inline]
>>   lock_acquire+0x202/0x310 kernel/locking/lockdep.c:3899
>>   __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
>>   _raw_spin_lock+0x2c/0x40 kernel/locking/spinlock.c:144
>>   spin_lock include/linux/spinlock.h:329 [inline]
>>   aio_poll fs/aio.c:1750 [inline]
>>   io_submit_one+0xb90/0x1b30 fs/aio.c:1853
>>   __do_sys_io_submit fs/aio.c:1919 [inline]
>>   __se_sys_io_submit fs/aio.c:1890 [inline]
>>   __x64_sys_io_submit+0x19b/0x500 fs/aio.c:1890
>>   do_syscall_64+0xc8/0x580 arch/x86/entry/common.c:290
>>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>   ......
>>   Allocated by task 4953:
>>   set_track mm/kasan/kasan.c:460 [inline]
>>   kasan_kmalloc+0xa0/0xd0 mm/kasan/kasan.c:553
>>   kmem_cache_alloc_trace+0x12f/0x2d0 mm/slub.c:2733
>>   kmalloc include/linux/slab.h:513 [inline]
>>   kzalloc include/linux/slab.h:707 [inline]
>>   alloc_pipe_info+0xdf/0x410 fs/pipe.c:633
>>   get_pipe_inode fs/pipe.c:712 [inline]
>>   create_pipe_files+0x98/0x780 fs/pipe.c:744
>>   __do_pipe_flags+0x35/0x230 fs/pipe.c:781
>>   do_pipe2+0x87/0x150 fs/pipe.c:829
>>   __do_sys_pipe2 fs/pipe.c:847 [inline]
>>   __se_sys_pipe2 fs/pipe.c:845 [inline]
>>   __x64_sys_pipe2+0x55/0x80 fs/pipe.c:845
>>   do_syscall_64+0xc8/0x580 arch/x86/entry/common.c:290
>>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>
>>  Freed by task 4952:
>>   set_track mm/kasan/kasan.c:460 [inline]
>>   __kasan_slab_free+0x12e/0x180 mm/kasan/kasan.c:521
>>   slab_free_hook mm/slub.c:1371 [inline]
>>   slab_free_freelist_hook mm/slub.c:1398 [inline]
>>   slab_free mm/slub.c:2953 [inline]
>>   kfree+0xeb/0x2f0 mm/slub.c:3906
>>   put_pipe_info+0xb0/0xd0 fs/pipe.c:556
>>   pipe_release+0x1ab/0x240 fs/pipe.c:577
>>   __fput+0x27f/0x7f0 fs/file_table.c:278
>>   task_work_run+0x136/0x1b0 kernel/task_work.c:113
>>   tracehook_notify_resume include/linux/tracehook.h:193 [inline]
>>   exit_to_usermode_loop+0x1a7/0x1d0 arch/x86/entry/common.c:166
>>   prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
>>   syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
>>   do_syscall_64+0x461/0x580 arch/x86/entry/common.c:293
>>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>
>> Fixes: bfe4037e722e ("aio: implement IOCB_CMD_POLL")
>> Cc: stable@vger.kernel.org [4.19+]
>> Signed-off-by: Hou Tao <houtao1@huawei.com>
>> ---
>>  fs/aio.c | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>>
>> diff --git a/fs/aio.c b/fs/aio.c
>> index aaaaf4d12c73..ea2f5de4feac 100644
>> --- a/fs/aio.c
>> +++ b/fs/aio.c
>> @@ -1763,6 +1763,12 @@ static ssize_t aio_poll(struct aio_kiocb *aiocb, const struct iocb *iocb)
>>  	/* one for removal from waitqueue, one for this function */
>>  	refcount_set(&aiocb->ki_refcnt, 2);
>>  
>> +	/*
>> +	 * file may be released by aio_poll_wake() if an expected event
>> +	 * is triggered immediately after the return of vfs_poll(), so
>> +	 * an extra reference is needed here to prevent use-after-free.
>> +	 */
>> +	get_file(req->file);
>>  	mask = vfs_poll(req->file, &apt.pt) & req->events;
>>  	if (unlikely(!req->head)) {
>>  		/* we did not manage to set up a waitqueue, done */
>> @@ -1788,6 +1794,8 @@ static ssize_t aio_poll(struct aio_kiocb *aiocb, const struct iocb *iocb)
>>  	spin_unlock_irq(&ctx->ctx_lock);
>>  
>>  out:
>> +	/* release the extra reference for vfs_poll() */
>> +	fput(req->file);
>>  	if (unlikely(apt.error)) {
>>  		fput(req->file);
>>  		return apt.error;
>>
> 
> 
> .
>