On Sun, Jun 04, 2017 at 01:24:13AM -0400, Matt Brown wrote:

On 06/03/2017 02:33 AM, Al Viro wrote:

quoted

On Sat, Jun 03, 2017 at 01:53:51AM -0400, Matt Brown wrote:

quoted

+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?

No, it needs to take a reference on the parent dentry before using it, using
dget_parent(), I think, and then dropping it later with dput().  Taking i_lock
isn't needed.

Eric
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