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Date:   Fri, 18 Jan 2019 23:26:34 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Christian Brauner <christian@brauner.io>
Cc:     gregkh@linuxfoundation.org, devel@driverdev.osuosl.org,
        linux-fsdevel@vger.kernel.org, tkjos@google.com
Subject: Re: [PATCH 0/5] binderfs: debug galore
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References: <20190118145344.11532-1-christian@brauner.io>
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On Fri, Jan 18, 2019 at 03:53:39PM +0100, Christian Brauner wrote:
> Hey everyone,
> 
> Al gave me a really helpful review of binderfs and pointed out a range
> of bugs. The most obvious and serious ones have fortunately already been
> taken care of by patches sitting in Greg's char-misc-linus tree. The
> others are hopefully all covered in this patchset.

BTW, binderfs_binder_device_create() looks rather odd - it would be easier
to do this:
        inode_lock(d_inode(root));
	/* look it up */
        dentry = lookup_one_len(name, root, strlen(name));
	if (IS_ERR(dentry)) {
		/* some kind of error (ENOMEM, permissions) - report */
		inode_unlock(d_inode(root));
		ret = PTR_ERR(dentry);
		goto err;
	}
	if (d_really_is_positive(dentry)) {
		/* already exists */
		dput(dentry);
		inode_unlock(d_inode(root));
		ret = -EEXIST;
		goto err;
	}
	inode->i_private = device;
... and from that point on - as in your variant.  Another thing in there:
        name = kmalloc(name_len, GFP_KERNEL);
        if (!name)
                goto err;

        strscpy(name, req->name, name_len);
is an odd way to go; more straightforward would be
	req->name[BINDERFS_MAX_NAME] = '\0';	/* NUL-terminate */
	name = kmemdup(req->name, sizeof(req->name), GEP_KERNEL);
	if (!name)
		....