linux-kernel - Re: [PATCH v3] ovl: fix null pointer when filesystemdoesn'tsupportdirect IO

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Date:   Tue, 28 Sep 2021 15:01:14 +0800
From:   Huang Jianan <huangjianan@...o.com>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     Chengguang Xu <cgxu519@....com>,
        overlayfs <linux-unionfs@...r.kernel.org>,
        linux-erofs@...ts.ozlabs.org, xiang@...nel.org, chao@...nel.org,
        guoweichao@...o.com, yh@...o.com, zhangshiming@...o.com,
        guanyuwei@...o.com, jnhuang95@...il.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Chengguang Xu <cgxu519@...ernel.net>
Subject: Re: [PATCH v3] ovl: fix null pointer when
 filesystemdoesn'tsupportdirect IO

在 2021/9/27 17:38, Miklos Szeredi 写道:
> On Wed, Sep 22, 2021 at 04:00:47PM +0200, Miklos Szeredi wrote:
>
>> First let's fix the oops: ovl_read_iter()/ovl_write_iter() must check
>> real file's ->direct_IO if IOCB_DIRECT is set in iocb->ki_flags and
>> return -EINVAL if not.
> And here's that fix.  Please test.

This patch can fix the oops.

Tested-by: Huang Jianan <huangjianan@...o.com>

Thanks,
Jianan

> Thanks,
> Miklos
>
> ---
> From: Miklos Szeredi <mszeredi@...hat.com>
> Subject: ovl: fix IOCB_DIRECT if underlying fs doesn't support direct IO
>
> Normally the check at open time suffices, but e.g loop device does set
> IOCB_DIRECT after doing its own checks (which are not sufficent for
> overlayfs).
>
> Make sure we don't call the underlying filesystem read/write method with
> the IOCB_DIRECT if it's not supported.
>
> Reported-by: Huang Jianan <huangjianan@...o.com>
> Fixes: 16914e6fc7e1 ("ovl: add ovl_read_iter()")
> Cc: <stable@...r.kernel.org> # v4.19
> Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
> ---
>   fs/overlayfs/file.c |   15 ++++++++++++++-
>   1 file changed, 14 insertions(+), 1 deletion(-)
>
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -296,6 +296,12 @@ static ssize_t ovl_read_iter(struct kioc
>   	if (ret)
>   		return ret;
>   
> +	ret = -EINVAL;
> +	if (iocb->ki_flags & IOCB_DIRECT &&
> +	    (!real.file->f_mapping->a_ops ||
> +	     !real.file->f_mapping->a_ops->direct_IO))
> +		goto out_fdput;
> +
>   	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,
> @@ -320,7 +326,7 @@ static ssize_t ovl_read_iter(struct kioc
>   out:
>   	revert_creds(old_cred);
>   	ovl_file_accessed(file);
> -
> +out_fdput:
>   	fdput(real);
>   
>   	return ret;
> @@ -349,6 +355,12 @@ static ssize_t ovl_write_iter(struct kio
>   	if (ret)
>   		goto out_unlock;
>   
> +	ret = -EINVAL;
> +	if (iocb->ki_flags & IOCB_DIRECT &&
> +	    (!real.file->f_mapping->a_ops ||
> +	     !real.file->f_mapping->a_ops->direct_IO))
> +		goto out_fdput;
> +
>   	if (!ovl_should_sync(OVL_FS(inode->i_sb)))
>   		ifl &= ~(IOCB_DSYNC | IOCB_SYNC);
>   
> @@ -384,6 +396,7 @@ static ssize_t ovl_write_iter(struct kio
>   	}
>   out:
>   	revert_creds(old_cred);
> +out_fdput:
>   	fdput(real);
>   
>   out_unlock: