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From: Rusty Russell <rusty@rustcorp.com.au>
To: Lucas De Marchi <lucas.de.marchi@gmail.com>
Cc: David Howells <dhowells@redhat.com>,
	dmitry.kasatkin@intel.com, zohar@linux.vnet.ibm.com,
	jmorris@namei.org, keyrings@linux-nfs.org,
	linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC] module: signature infrastructure
Date: Wed, 05 Sep 2012 09:49:55 +0930	[thread overview]
Message-ID: <874nndl3ro.fsf@rustcorp.com.au> (raw)
In-Reply-To: <CAKi4VALezG7VccXJfwvzr2UZrmAjCUp9eZRjGwqq6cWcExNqXA@mail.gmail.com>

Lucas De Marchi <lucas.de.marchi@gmail.com> writes:
> Hi Rusty,
>
> On Tue, Sep 4, 2012 at 2:55 AM, Rusty Russell <rusty@rustcorp.com.au> wrote:
>> @@ -2399,7 +2437,50 @@ static inline void kmemleak_load_module(const struct module *mod,
>>  }
>>  #endif
>>
>> -/* Sets info->hdr and info->len. */
>> +#ifdef CONFIG_MODULE_SIG
>> +static int module_sig_check(struct load_info *info,
>> +                           void *mod, unsigned long *len)
>> +{
>> +       int err;
>> +       unsigned long i, siglen;
>> +       char *sig = NULL;
>> +
>> +       /* This is not a valid module: ELF header is larger anyway. */
>> +       if (*len < sizeof(MODULE_SIG_STRING))
>> +               return -ENOEXEC;
>> +
>> +       for (i = 0; i < *len - (sizeof(MODULE_SIG_STRING)-1); i++) {
>> +               /* Our memcmp is dumb, speed it up a little. */
>> +               if (((char *)mod)[i] != MODULE_SIG_STRING[0])
>> +                       continue;
>
> Since the signature is appended to the module, why don't you go
> backwards, starting from *len - strlen(sizeof(MODULE_SIG_STRING)) and
> making this first comparison?

We've had this discussion multiple times.  Simple wins.  It's so
marginal, I don't really care, but I've changed it to:

	int err;
	unsigned long i, siglen, markerlen;
	char *sig = NULL;

	markerlen = strlen(MODULE_SIG_STRING);
	/* This is not a valid module: ELF header is larger anyway. */
	if (*len < markerlen)
		return -ENOEXEC;

	for (i = *len - markerlen; i > 0; i--) {
		/* Our memcmp is dumb, speed it up a little. */
		if (((char *)mod)[i] != MODULE_SIG_STRING[0])
			continue;
		if (memcmp(mod+i, MODULE_SIG_STRING, markerlen))
			continue;

		sig = mod + i + markerlen;
		siglen = *len - i - markerlen;
		*len = i;
		break;
	}

We could also implement memrchr(), or memrmem().  Hell, if we had
memmem() in the kernel I'd gladly use it.

> Or let the magic string as the last thing in the module and store the
> signature length, too. In this case no scanning is needed

Yes, they did that too, but append is simpler.  I don't even have to
think about endianness (Dmitry chose be32) or parsing (David chose
5-digit ascii numeric encoding).

Scanning the module is the least of our issues since we've just copied
it and we're about to SHA it.

Cheers,
Rusty.

  parent reply	other threads:[~2012-09-05  8:22 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-08-16  1:34 [PATCH 00/25] Crypto keys and module signing David Howells
2012-08-16  1:34 ` [PATCH 01/25] KEYS: Add payload preparsing opportunity prior to key instantiate or update David Howells
2012-08-16  1:34 ` [PATCH 02/25] MPILIB: Provide count_leading/trailing_zeros() based on arch functions David Howells
2012-09-10  7:13   ` Kasatkin, Dmitry
2012-09-13  5:14     ` James Morris
2012-09-13 14:09       ` Kasatkin, Dmitry
2012-08-16  1:34 ` [PATCH 03/25] KEYS: Create a key type that can be used for general cryptographic operations David Howells
2012-08-16  1:34 ` [PATCH 04/25] KEYS: Add signature verification facility David Howells
2012-08-16  1:35 ` [PATCH 05/25] KEYS: Asymmetric public-key algorithm crypto key subtype David Howells
2012-08-16  1:35 ` [PATCH 06/25] MPILIB: Reinstate mpi_cmp[_ui]() and export for RSA signature verification David Howells
2012-08-16  1:35 ` [PATCH 07/25] KEYS: RSA: Implement signature verification algorithm [PKCS#1 / RFC3447] David Howells
2012-08-16  1:35 ` [PATCH 08/25] KEYS: RSA: Fix signature verification for shorter signatures David Howells
2012-08-16  1:35 ` [PATCH 09/25] PGPLIB: PGP definitions (RFC 4880) David Howells
2012-08-16  1:36 ` [PATCH 10/25] PGPLIB: Basic packet parser David Howells
2012-08-16  1:36 ` [PATCH 11/25] PGPLIB: Signature parser David Howells
2012-08-16  1:36 ` [PATCH 12/25] KEYS: PGP data parser David Howells
2012-08-16  1:36 ` [PATCH 13/25] KEYS: PGP-based public key signature verification David Howells
2012-08-16  1:36 ` [PATCH 14/25] KEYS: PGP format signature parser David Howells
2012-08-16  1:36 ` [PATCH 15/25] KEYS: Provide PGP key description autogeneration David Howells
2012-08-16  1:37 ` [PATCH 16/25] KEYS: Provide a function to load keys from a PGP keyring blob David Howells
2012-08-16  1:37 ` [PATCH 17/25] MODSIGN: Provide gitignore and make clean rules for extra files David Howells
2012-08-16  1:37 ` [PATCH 18/25] MODSIGN: Provide Documentation and Kconfig options David Howells
2012-08-16  1:37 ` [PATCH 19/25] MODSIGN: Sign modules during the build process David Howells
2012-08-16  1:37 ` [PATCH 20/25] MODSIGN: Provide module signing public keys to the kernel David Howells
2012-08-31 14:33   ` Michal Marek
2012-08-16  1:38 ` [PATCH 21/25] MODSIGN: Module signature verification David Howells
2012-08-16  1:38 ` [PATCH 22/25] MODSIGN: Automatically generate module signing keys if missing David Howells
2012-08-16  1:38 ` [PATCH 23/25] MODSIGN: Panic the kernel if FIPS is enabled upon module signing failure David Howells
2012-08-16  1:38 ` [PATCH 24/25] MODSIGN: Allow modules to be signed with an unknown key unless enforcing David Howells
2012-08-16  1:38 ` [PATCH 25/25] MODSIGN: Fix documentation of signed-nokey behavior when not enforcing David Howells
2012-08-21  5:04 ` [PATCH 00/25] Crypto keys and module signing Rusty Russell
2012-08-22 10:50 ` David Howells
2012-08-22 11:52   ` Mimi Zohar
2012-08-22 16:07   ` Kasatkin, Dmitry
2012-09-04  5:55 ` [RFC] module: signature infrastructure Rusty Russell
2012-09-04 12:07   ` Kasatkin, Dmitry
2012-09-04 12:21     ` Kasatkin, Dmitry
2012-09-04 13:40       ` Mimi Zohar
2012-09-05  0:29     ` Rusty Russell
2012-09-05 13:34       ` Mimi Zohar
2012-09-06  2:05         ` Rusty Russell
2012-09-04 14:25   ` Lucas De Marchi
2012-09-04 15:04     ` Kasatkin, Dmitry
2012-09-05  0:19     ` Rusty Russell [this message]
2012-09-05 23:41       ` Lucas De Marchi
2012-09-06  7:55         ` Rusty Russell
2012-09-04 22:51   ` David Howells
2012-09-04 23:17     ` Kasatkin, Dmitry

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