Re: [PATCH v3 2/4] xfs: initialize inode security on tmpfile creation

[Christoph Hellwig <hch@infradead.org>]

On Tue, Apr 15, 2014 at 04:04:32PM -0400, Stephen Smalley wrote:
> Is there a reason that xfs_init_security() isn't called from the inode
> allocation function (e.g. xfs_ialloc), as in ext4 (__ext4_new_inode
> calls ext4_init_security and also calls ext4_init_acl)?  That would have
> ensured that tmpfile inodes would have been labeled without requiring a
> separate change and more generally ensures complete coverage for all inodes.

Really just code structuring - we don't like callouts to high level VFS
functions from deep down in the guts of the filesystem.

> For SELinux, we need the tmpfile inodes to be labeled at creation time,
> not just if linked into the namespace, since they may be shared via
> local socket IPC or inherited across a label-changing exec and since we
> revalidate access on transfer or use.
> 
> Labeling based on the provided directory could be a bit random, although
> it will work out with current policy if the provided directory
> corresponds to existing tmpfile locations (e.g. /tmp, /var/tmp) and
> therefore already has a label associated with temporary files.
> Otherwise we might want some indication that it is a tmpfile passed into
> security_inode_init_security() so that we can always select a stable
> label irrespective of the directory.

Just check for I_LINKABLE in i_flags.