linux-kernel - Re: [PATCH 08a/30] kexec_file: split KEXEC_VERIFY_SIG into KEXEC_SIG and KEXEC_SIG

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Date:   Tue, 16 Jan 2018 16:31:51 +0000
From:   David Howells <dhowells@...hat.com>
To:     Jiri Bohac <jbohac@...e.cz>
Cc:     dhowells@...hat.com, linux-security-module@...r.kernel.org,
        gnomes@...rguk.ukuu.org.uk, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, jforbes@...hat.com,
        Chun-Yi Lee <joeyli.kernel@...il.com>
Subject: Re: [PATCH 08a/30] kexec_file: split KEXEC_VERIFY_SIG into KEXEC_SIG and KEXEC_SIG_FORCE

I think that your code isn't quite right.  Looking at the patched code:

    #ifdef CONFIG_KEXEC_SIG
	sig_err = arch_kexec_kernel_verify_sig(image, image->kernel_buf,
					   image->kernel_buf_len);
	if (sig_err)
		pr_debug("kernel signature verification failed.\n");
	else
		pr_debug("kernel signature verification successful.\n");
    #endif

	if (sig_err && IS_ENABLED(CONFIG_KEXEC_SIG_FORCE)) {
		ret = sig_err;
		goto out;
	}

If the signature check fails because the signature is bad, but
CONFIG_KEXEC_SIG_FORCE=n then it now won't fail when it should.

If sig_err is -EKEYREJECTED, -EKEYEXPIRED or -EKEYREVOKED then it must fail,
even if the signature check isn't forced.

David