linux-ext4 - Re: [PATCH 2/5] ext2: preserve i_mode if ext2_set

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Message-ID: <20170717163304.GB22195@quack2.suse.cz>
Date:   Mon, 17 Jul 2017 18:33:04 +0200
From:   Jan Kara <jack@...e.cz>
To:     Ernesto A. Fernández 
        <ernesto.mnd.fernandez@...il.com>
Cc:     Jan Kara <jack@...e.com>, Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Dave Kleikamp <shaggy@...nel.org>, linux-ext4@...r.kernel.org,
        jfs-discussion@...ts.sourceforge.net,
        reiserfs-devel@...r.kernel.org
Subject: Re: [PATCH 2/5] ext2: preserve i_mode if ext2_set_acl() fails

On Wed 12-07-17 06:54:19, Ernesto A. Fernández wrote:
> When changing a file's acl mask, ext2_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.
> 
> Signed-off-by: Ernesto A. Fernández <ernesto.mnd.fernandez@...il.com>

Thanks for the patch! I have rebased it on top of the fix in that area that
is sitting in my tree and merged it to my tree.

								Honza

> ---
> A line in acl.c is too long, and checkpatch.pl complains about it when run
> against this patch. In case it matters, the next patch will fix that.
> 
>  fs/ext2/acl.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ext2/acl.c b/fs/ext2/acl.c
> index 79dafa7..4e04b7e 100644
> --- a/fs/ext2/acl.c
> +++ b/fs/ext2/acl.c
> @@ -185,16 +185,17 @@ ext2_set_acl(struct inode *inode, struct posix_acl *acl, int type)
>  	void *value = NULL;
>  	size_t size = 0;
>  	int error;
> +	int update_mode = 0;
> +	umode_t mode = inode->i_mode;
>  
>  	switch(type) {
>  		case ACL_TYPE_ACCESS:
>  			name_index = EXT2_XATTR_INDEX_POSIX_ACL_ACCESS;
>  			if (acl) {
> -				error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
> +				error = posix_acl_update_mode(inode, &mode, &acl);
>  				if (error)
>  					return error;
> -				inode->i_ctime = current_time(inode);
> -				mark_inode_dirty(inode);
> +				update_mode = 1;
>  			}
>  			break;
>  
> @@ -216,8 +217,14 @@ ext2_set_acl(struct inode *inode, struct posix_acl *acl, int type)
>  	error = ext2_xattr_set(inode, name_index, "", value, size, 0);
>  
>  	kfree(value);
> -	if (!error)
> +	if (!error) {
>  		set_cached_acl(inode, type, acl);
> +		if (update_mode) {
> +			inode->i_mode = mode;
> +			inode->i_ctime = current_time(inode);
> +			mark_inode_dirty(inode);
> +		}
> +	}
>  	return error;
>  }
>  
> -- 
> 2.1.4
> 
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR