Re: [PATCH v1 1/1] Add Trusted Path Execution as a stackable LSM

[Matt Brown]

On 06/03/2017 02:33 AM, Al Viro wrote:
> On Sat, Jun 03, 2017 at 01:53:51AM -0400, Matt Brown wrote:
>
> > +static int tpe_bprm_set_creds(struct linux_binprm *bprm)
> > +{
> > +	struct file *file = bprm->file;
> > +	struct inode *inode = d_backing_inode(file->f_path.dentry->d_parent);
> > +	struct inode *file_inode = d_backing_inode(file->f_path.dentry);
>
> Bloody wonderful.  Do tell, what *does* prevent a race with rename(2) here,
> somehow making sure that your 'inode' won't get freed right under you?

Good catch. How does this look:

spin_lock(&inode->i_lock);
spin_lock(&file_inode->i_lock);
if (global_nonroot(inode->i_uid) && !uid_eq(inode->i_uid, cred->uid))
	reason1 = "directory not owned by user";
else if (inode->i_mode & 0002)
	reason1 = "file in world-writable directory";
else if ((inode->i_mode & 0020) && global_nonroot_gid(inode->i_gid))
	reason1 = "file in group-writable directory";
else if (file_inode->i_mode & 0002)
	reason1 = "file is world-writable";
spin_unlock(&inode->i_lock);
spin_unlock(&file_inode->i_lock);

and likewise for other places in the code?