From: Huang Jianan <huangjianan@oppo.com>
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: guoweichao@oppo.com, yh@oppo.com, zhangshiming@oppo.com,
guanyuwei@oppo.com, jnhuang95@gmail.com,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v3] ovl: fix null pointer when filesystem doesn't support direct IO
Date: Wed, 22 Sep 2021 16:24:56 +0800 [thread overview]
Message-ID: <919e929d-6af7-b729-9fd2-954cd1e52999@oppo.com> (raw)
In-Reply-To: <e42a183f-274c-425f-2012-3ff0003e1fcb@139.com>
在 2021/9/22 16:06, Chengguang Xu 写道:
> 在 2021/9/22 15:23, 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:
>
> I just looked around the code more closely, in open_with_fake_path(),
>
> do_dentry_open() has already checked O_DIRECT open flag and
> a_ops->direct_IO of underlying real address_space.
>
> Am I missing something?
>
>
It seems that loop_update_dio will set lo->use_dio after open file
without set O_DIRECT.
loop_update_dio will check f_mapping->a_ops->direct_IO but it deal with
ovl_aops with
noop _direct_IO.
So I think we still need a new aops?
Thanks,
Jianan
> Thanks,
>
> Chengguang
>
>
>>
>> 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 return
>> -EINVAL when the file doesn't support direct_IO to fix this problem.
>>
>> Fixes: 5b910bd615ba ("ovl: fix GPF in swapfile_activate of file from
>> overlayfs over xfs")
>> Signed-off-by: Huang Jianan <huangjianan@oppo.com>
>> ---
>> change since v2:
>> - Return error in ovl_open directly. (Chengguang Xu)
>>
>> Change since v1:
>> - Return error to user rather than fall back to buffered io.
>> (Chengguang Xu)
>>
>> fs/overlayfs/file.c | 4 ++++
>> 1 file changed, 4 insertions(+)
>>
>> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
>> index d081faa55e83..a0c99ea35daf 100644
>> --- a/fs/overlayfs/file.c
>> +++ b/fs/overlayfs/file.c
>> @@ -157,6 +157,10 @@ static int ovl_open(struct inode *inode, struct
>> file *file)
>> if (IS_ERR(realfile))
>> return PTR_ERR(realfile);
>> + if ((f->f_flags & O_DIRECT) && (!realfile->f_mapping->a_ops ||
>> + !realfile->f_mapping->a_ops->direct_IO))
>> + return -EINVAL;
>> +
>> file->private_data = realfile;
>> return 0;
>
next prev parent reply other threads:[~2021-09-22 8:25 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-18 12:13 [PATCH] ovl: fix null pointer when filesystem doesn't support direct IO Huang Jianan
2021-09-22 1:56 ` Chengguang Xu
2021-09-22 3:39 ` Huang Jianan
2021-09-22 3:47 ` [PATCH v2] " Huang Jianan
2021-09-22 5:09 ` Chengguang Xu
2021-09-22 7:18 ` Huang Jianan
2021-09-22 7:23 ` [PATCH v3] " Huang Jianan
2021-09-22 8:06 ` Chengguang Xu
2021-09-22 8:24 ` Huang Jianan [this message]
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
2021-09-28 7:17 ` Miklos Szeredi
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