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From: Huang Jianan via Linux-erofs <linux-erofs@lists.ozlabs.org>
To: Chengguang Xu <cgxu519@139.com>,
	linux-unionfs@vger.kernel.org, miklos@szeredi.hu,
	linux-erofs@lists.ozlabs.org, xiang@kernel.org, chao@kernel.org
Cc: zhangshiming@oppo.com, linux-kernel@vger.kernel.org, yh@oppo.com,
	guanyuwei@oppo.com, linux-fsdevel@vger.kernel.org,
	guoweichao@oppo.com
Subject: Re: [PATCH] ovl: fix null pointer when filesystem doesn't support direct IO
Date: Wed, 22 Sep 2021 11:39:18 +0800	[thread overview]
Message-ID: <76cfd82b-47c8-d5aa-e946-f9e53f78ad81@oppo.com> (raw)
In-Reply-To: <3633c6e5-028c-fc77-3b8e-da9903f97ac5@139.com>

在 2021/9/22 9:56, Chengguang Xu 写道:
> 在 2021/9/18 20:13, Huang Jianan 写道:
>> From: Huang Jianan <huangjianan@oppo.com>
>>
>> At present, overlayfs provides overlayfs inode to users. Overlayfs
>> inode provides ovl_aops with noop_direct_IO to avoid open failure
>> with O_DIRECT. But some compressed filesystems, such as erofs and
>> squashfs, don't support direct_IO.
>>
>> Users who use f_mapping->a_ops->direct_IO to check O_DIRECT support,
>> will read file through this way. This will cause overlayfs to access
>> a non-existent direct_IO function and cause panic due to null pointer:
>>
>> Kernel panic - not syncing: CFI failure (target: 0x0)
>> CPU: 6 PID: 247 Comm: loop0
>> Call Trace:
>>   panic+0x188/0x45c
>>   __cfi_slowpath+0x0/0x254
>>   __cfi_slowpath+0x200/0x254
>>   generic_file_read_iter+0x14c/0x150
>>   vfs_iocb_iter_read+0xac/0x164
>>   ovl_read_iter+0x13c/0x2fc
>>   lo_rw_aio+0x2bc/0x458
>>   loop_queue_work+0x4a4/0xbc0
>>   kthread_worker_fn+0xf8/0x1d0
>>   loop_kthread_worker_fn+0x24/0x38
>>   kthread+0x29c/0x310
>>   ret_from_fork+0x10/0x30
>>
>> The filesystem may only support direct_IO for some file types. For
>> example, erofs supports direct_IO for uncompressed files. So fall
>> back to buffered io only when the file doesn't support direct_IO to
>> fix this problem.
>
>
> IMO, return error to user seems better option than fall back to
>
> buffered io directly.
>
Agreed, I will send v2 to fix it.

Thanks,
Jianan
>
> Thanks,
>
> Chengguang
>
>
>>
>> Fixes: 5b910bd615ba ("ovl: fix GPF in swapfile_activate of file from 
>> overlayfs over xfs")
>> Signed-off-by: Huang Jianan <huangjianan@oppo.com>
>> ---
>>   fs/overlayfs/file.c | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
>> index d081faa55e83..998c60770b81 100644
>> --- a/fs/overlayfs/file.c
>> +++ b/fs/overlayfs/file.c
>> @@ -296,6 +296,10 @@ static ssize_t ovl_read_iter(struct kiocb *iocb, 
>> struct iov_iter *iter)
>>       if (ret)
>>           return ret;
>>   +    if ((iocb->ki_flags & IOCB_DIRECT) && 
>> (!real.file->f_mapping->a_ops ||
>> +        !real.file->f_mapping->a_ops->direct_IO))
>> +        iocb->ki_flags &= ~IOCB_DIRECT;
>> +
>>       old_cred = ovl_override_creds(file_inode(file)->i_sb);
>>       if (is_sync_kiocb(iocb)) {
>>           ret = vfs_iter_read(real.file, iter, &iocb->ki_pos,
>


  reply	other threads:[~2021-09-22  3:40 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-18 12:13 Huang Jianan via Linux-erofs
2021-09-22  1:56 ` Chengguang Xu
2021-09-22  3:39   ` Huang Jianan via Linux-erofs [this message]
2021-09-22  3:47 ` [PATCH v2] " Huang Jianan via Linux-erofs
2021-09-22  5:09   ` Chengguang Xu
2021-09-22  7:18     ` Huang Jianan via Linux-erofs
2021-09-22  7:23       ` [PATCH v3] " Huang Jianan via Linux-erofs
2021-09-22  8:06         ` Chengguang Xu
2021-09-22  8:24           ` Huang Jianan via Linux-erofs
2021-09-22 13:20             ` [PATCH v3] ovl: fix null pointer when filesystemdoesn'tsupportdirect IO Chengguang Xu
2021-09-22 14:00               ` Miklos Szeredi
2021-09-27  9:38                 ` Miklos Szeredi
2021-09-28  7:01                   ` Huang Jianan via Linux-erofs
2021-09-28  7:17                     ` Miklos Szeredi

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