Re: [PATCH 2/2] ecryptfs: don't allow mmap when the lower fs doesn't support it

[Jann Horn <jann@thejh.net>]

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On Tue, Jul 05, 2016 at 05:32:30PM -0400, jeffm@suse.com wrote:
> From: Jeff Mahoney <jeffm@suse.com>
> 
> There are legitimate reasons to disallow mmap on certain files, notably
> in sysfs or procfs.  We shouldn't emulate mmap support on file systems
> that don't offer support natively.
> 
> Signed-off-by: Jeff Mahoney <jeffm@suse.com>
> ---
>  fs/ecryptfs/file.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ecryptfs/file.c b/fs/ecryptfs/file.c
> index 7000b96..4aaa656 100644
> --- a/fs/ecryptfs/file.c
> +++ b/fs/ecryptfs/file.c
> @@ -169,6 +169,20 @@ out:
>  	return rc;
>  }
>  
> +
> +static int ecryptfs_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> +	struct dentry *dentry = ecryptfs_dentry_to_lower(file_dentry(file));
> +	/*
> +	 * Don't allow mmap on top of file systems that don't support it
> +	 * natively.  If FILESYSTEM_MAX_STACK_DEPTH > 2 or ecryptfs
> +	 * allows recursive mounting, this will need to be extended.

Or if another new stacking filesystem appears whose f_op->mmap just forwards
to lower_f_op->mmap - but thinking about it, in that scenario, my patch
would stop working, too.

At this point, I dislike both this patch and my own one because of their
lack of robustness. Well, at least e54ad7f1ee263ffa5a2de9c609d58dfa27b21cd9
should be solid. :/


> +	 */
> +	if (!d_inode(dentry)->i_fop->mmap)
> +		return -ENODEV;
> +	return generic_file_mmap(file, vma);
> +}
> +
>  /**
>   * ecryptfs_open
>   * @inode: inode speciying file to open
> @@ -403,7 +417,7 @@ const struct file_operations ecryptfs_main_fops = {
>  #ifdef CONFIG_COMPAT
>  	.compat_ioctl = ecryptfs_compat_ioctl,
>  #endif
> -	.mmap = generic_file_mmap,
> +	.mmap = ecryptfs_mmap,
>  	.open = ecryptfs_open,
>  	.flush = ecryptfs_flush,
>  	.release = ecryptfs_release,
> -- 
> 2.7.1
> 

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