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

[Bill O'Donnell <billodo@redhat.com>]

On Thu, Dec 07, 2017 at 11:31:51AM -0600, Bill O'Donnell wrote:
> 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
> 
> Sorry, I'm coming into this late, and might be missing something...
> is there a particular xfs configuration that you've set up on which
> generic/449 fails? On 4.15-rc1, I see no failures of g/449.

Oh, I see this was merged and fixes g/449:
commit 67f2ffe31d1a683170c2ba0ecc643e42a5fdd397
Author: Dave Chinner <dchinner@redhat.com>
Date:   Mon Oct 9 11:37:23 2017 -0700

    xfs: don't change inode mode if ACL update fails



> 
> Thanks-
> Bill
> 
> 
> 
> > 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
> > 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.
> > 
> >  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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