linux-kernel - Re: [PATCH v3 3/4] add kexec

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Date:   Thu, 2 May 2019 17:58:36 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     Prakhar Srivastava <prsriva02@...il.com>,
        linux-integrity@...r.kernel.org,
        linux-secuirty-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, ebiederm@...ssion.com,
        vgoyal@...hat.com, nayna@...ux.ibm.com
Subject: Re: [PATCH v3 3/4] add kexec_cmdline used to ima

On Thu, May 02, 2019 at 12:52:35PM -0400, Mimi Zohar wrote:
> On Mon, 2019-04-29 at 14:47 -0700, Prakhar Srivastava wrote:
> > From: Prakhar Srivastava <prsriva02@...il.com>

> kexec doesn't really know or care about IMA.  Other than the IMA call,
> itself, nothing should be added to kexec files.  As mentioned in 1/4,
> the IMA hook would be named something like ima_kexec_cmdline().

> > +	f = fdget(kernel_fd);
> > +	if (!f.file)
> > +		goto out;
> > +
> > +	size = (f.file->f_path.dentry->d_name.len + cmdline_len - 1+
> > +			ARRAY_SIZE(delimiter)) - 1;
> > +
> > +	buf = kzalloc(size, GFP_KERNEL);
> > +	if (!buf)
> > +		goto out;
> > +
> > +	memcpy(buf, f.file->f_path.dentry->d_name.name,
> > +		f.file->f_path.dentry->d_name.len);
> > +	memcpy(buf + f.file->f_path.dentry->d_name.len,
> > +		delimiter, ARRAY_SIZE(delimiter) - 1);
> > +	memcpy(buf + f.file->f_path.dentry->d_name.len +
> > +		ARRAY_SIZE(delimiter) - 1,
> > +		cmdline_ptr, cmdline_len - 1);

Another thing is that it's so obviously racy, it's not even funny.
Consider what rename(2) in parallel will do to that.