Re: [PATCH] xfs: preserve i_mode if __xfs_set_acl() fails

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Mon, Aug 14, 2017 at 05:18:10AM -0300, Ernesto A. Fernández wrote:
> When changing a file's ACL mask, xfs_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.
> 
> To prevent this, perform the mode update and the ACL update as part of
> the same transaction, and restore the original mode to the vfs inode in
> case of failure. This requires a change in how extended attributes are
> deleted: commit the transaction even if there was no attribute to
> remove, to log the standard inode fields.
> 
> Signed-off-by: Ernesto A. Fernández <ernesto.mnd.fernandez@gmail.com>
> ---
> This issue is covered by generic/449 in xfstests. Several other filesystems
> are affected by this, some of them have already applied patches:
>   - 397e434 ext4: preserve i_mode if __ext4_set_acl() fails
>   - f070e5a jfs: preserve i_mode if __jfs_set_acl() fails
>   - fcea8ae reiserfs: preserve i_mode if __reiserfs_set_acl() fails
>   - fe26569 ext2: preserve i_mode if ext2_set_acl() fails
> The test won't exactly pass after this patch is applied. It will fail
> differently, this time claiming that the filesystem is inconsistent. This

I disagree that corrupting the filesystem is an acceptable strategy for
dealing with insufficient space to handle setfacl.

> probably has something to do with setting too many extended attributes, as
> it goes away if you change the attribute size in the test from 1k to 64k.

Hadn't you better look into why it does that and handle it?

--D

> 
>  fs/xfs/libxfs/xfs_attr.c | 13 +++++++++++--
>  fs/xfs/xfs_acl.c         | 39 ++++++++++++++-------------------------
>  2 files changed, 25 insertions(+), 27 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> index de7b9bd..c3193e1 100644
> --- a/fs/xfs/libxfs/xfs_attr.c
> +++ b/fs/xfs/libxfs/xfs_attr.c
> @@ -395,6 +395,7 @@ xfs_attr_remove(
>  	struct xfs_defer_ops	dfops;
>  	xfs_fsblock_t		firstblock;
>  	int			error;
> +	int			noattr = 0;
>  
>  	XFS_STATS_INC(mp, xs_attr_remove);
>  
> @@ -438,7 +439,12 @@ xfs_attr_remove(
>  	xfs_trans_ijoin(args.trans, dp, 0);
>  
>  	if (!xfs_inode_hasattr(dp)) {
> -		error = -ENOATTR;
> +		/*
> +		 * Commit even if there is no attr to remove, because when
> +		 * setting ACLs the caller may be changing the mode in the
> +		 * same transaction.
> +		 */
> +		noattr = 1;
>  	} else if (dp->i_d.di_aformat == XFS_DINODE_FMT_LOCAL) {
>  		ASSERT(dp->i_afp->if_flags & XFS_IFINLINE);
>  		error = xfs_attr_shortform_remove(&args);
> @@ -458,7 +464,7 @@ xfs_attr_remove(
>  	if (mp->m_flags & XFS_MOUNT_WSYNC)
>  		xfs_trans_set_sync(args.trans);
>  
> -	if ((flags & ATTR_KERNOTIME) == 0)
> +	if ((flags & ATTR_KERNOTIME) == 0 && !noattr)
>  		xfs_trans_ichgtime(args.trans, dp, XFS_ICHGTIME_CHG);
>  
>  	/*
> @@ -468,6 +474,9 @@ xfs_attr_remove(
>  	error = xfs_trans_commit(args.trans);
>  	xfs_iunlock(dp, XFS_ILOCK_EXCL);
>  
> +	if (!error && noattr)
> +		error = -ENOATTR;
> +
>  	return error;
>  
>  out:
> diff --git a/fs/xfs/xfs_acl.c b/fs/xfs/xfs_acl.c
> index 7034e17..1fe4363 100644
> --- a/fs/xfs/xfs_acl.c
> +++ b/fs/xfs/xfs_acl.c
> @@ -226,28 +226,13 @@ __xfs_set_acl(struct inode *inode, struct posix_acl *acl, int type)
>  	return error;
>  }
>  
> -static int
> -xfs_set_mode(struct inode *inode, umode_t mode)
> -{
> -	int error = 0;
> -
> -	if (mode != inode->i_mode) {
> -		struct iattr iattr;
> -
> -		iattr.ia_valid = ATTR_MODE | ATTR_CTIME;
> -		iattr.ia_mode = mode;
> -		iattr.ia_ctime = current_time(inode);
> -
> -		error = xfs_setattr_nonsize(XFS_I(inode), &iattr, XFS_ATTR_NOACL);
> -	}
> -
> -	return error;
> -}
> -
>  int
>  xfs_set_acl(struct inode *inode, struct posix_acl *acl, int type)
>  {
>  	int error = 0;
> +	int mode_changed = 0;
> +	umode_t old_mode = inode->i_mode;
> +	struct timespec old_ctime = inode->i_ctime;
>  
>  	if (!acl)
>  		goto set_acl;
> @@ -257,16 +242,20 @@ xfs_set_acl(struct inode *inode, struct posix_acl *acl, int type)
>  		return error;
>  
>  	if (type == ACL_TYPE_ACCESS) {
> -		umode_t mode;
> -
> -		error = posix_acl_update_mode(inode, &mode, &acl);
> -		if (error)
> -			return error;
> -		error = xfs_set_mode(inode, mode);
> +		error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
>  		if (error)
>  			return error;
> +		inode->i_ctime = current_time(inode);
> +		XFS_STATS_INC(XFS_I(inode)->i_mount, xs_ig_attrchg);
> +		mode_changed = 1;
>  	}
>  
>   set_acl:
> -	return __xfs_set_acl(inode, acl, type);
> +	error = __xfs_set_acl(inode, acl, type);
> +	if (error && mode_changed) {
> +		inode->i_mode = old_mode;
> +		inode->i_ctime = old_ctime;
> +		XFS_STATS_DEC(XFS_I(inode)->i_mount, xs_ig_attrchg);
> +	}
> +	return error;
>  }
> -- 
> 2.1.4
> 
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