linux-ext4 - Re: [PATCH 4/5] jfs: preserve i_mode if __jfs_set

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Date:   Thu, 13 Jul 2017 16:01:42 -0500
From:   Dave Kleikamp <dave.kleikamp@...cle.com>
To:     "Ernesto A. Fernández" 
        <ernesto.mnd.fernandez@...il.com>, Jan Kara <jack@...e.com>,
        "Theodore Ts'o" <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org, jfs-discussion@...ts.sourceforge.net,
        reiserfs-devel@...r.kernel.org
Subject: Re: [PATCH 4/5] jfs: preserve i_mode if __jfs_set_acl() fails

On 07/12/2017 04:55 AM, Ernesto A. Fernández wrote:
> When changing a file's acl mask, __jfs_set_acl() will first set the group
> bits of i_mode to the value of the mask, and only then set the actual
> extended attribute representing the new acl.
> 
> If the second part fails (due to lack of space, for example) and the file
> had no acl attribute to begin with, the system will from now on assume
> that the mask permission bits are actual group permission bits, potentially
> granting access to the wrong users.
> 
> Prevent this by only changing the inode mode after the acl has been set.

This looks good to me. I'll add it to the jfs queue.

Thanks,
Shaggy

> 
> Signed-off-by: Ernesto A. Fernández <ernesto.mnd.fernandez@...il.com>
> ---
>  fs/jfs/acl.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/jfs/acl.c b/fs/jfs/acl.c
> index 7bc186f..db5a385 100644
> --- a/fs/jfs/acl.c
> +++ b/fs/jfs/acl.c
> @@ -73,16 +73,17 @@ static int __jfs_set_acl(tid_t tid, struct inode *inode, int type,
>  	int rc;
>  	int size = 0;
>  	char *value = NULL;
> +	int update_mode = 0;
> +	umode_t mode = inode->i_mode;
>  
>  	switch (type) {
>  	case ACL_TYPE_ACCESS:
>  		ea_name = XATTR_NAME_POSIX_ACL_ACCESS;
>  		if (acl) {
> -			rc = posix_acl_update_mode(inode, &inode->i_mode, &acl);
> +			rc = posix_acl_update_mode(inode, &mode, &acl);
>  			if (rc)
>  				return rc;
> -			inode->i_ctime = current_time(inode);
> -			mark_inode_dirty(inode);
> +			update_mode = 1;
>  		}
>  		break;
>  	case ACL_TYPE_DEFAULT:
> @@ -105,8 +106,14 @@ static int __jfs_set_acl(tid_t tid, struct inode *inode, int type,
>  out:
>  	kfree(value);
>  
> -	if (!rc)
> +	if (!rc) {
>  		set_cached_acl(inode, type, acl);
> +		if (update_mode) {
> +			inode->i_mode = mode;
> +			inode->i_ctime = current_time(inode);
> +			mark_inode_dirty(inode);
> +		}
> +	}
>  
>  	return rc;
>  }
>