Re: [PATCH v5 12/18] MODSIGN: Export module signature definitions

Thiago Jung Bauermann
2017-10-26T22:47:45Z

Mimi Zohar <zohar@linux.vnet.ibm.com> writes:

> On Tue, 2017-10-17 at 22:53 -0200, Thiago Jung Bauermann wrote:
>> IMA will use the module_signature format for append signatures, so export
>> the relevant definitions and factor out the code which verifies that the
>> appended signature trailer is valid.
>>
>> Also, create a CONFIG_MODULE_SIG_FORMAT option so that IMA can select it
>> and be able to use validate_module_signature without having to depend on
>> CONFIG_MODULE_SIG.
>>
>> Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
>
> Reviewed-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
>
> One minor comment below...

Thanks!

>> diff --git a/kernel/module_signing.c b/kernel/module_signing.c
>> index 937c844bee4a..204c60d4cc9f 100644
>> --- a/kernel/module_signing.c
>> +++ b/kernel/module_signing.c
>> @@ -11,36 +11,38 @@
>>
>> #include <linux/kernel.h>
>> #include <linux/errno.h>
>> +#include <linux/module_signature.h>
>> #include <linux/string.h>
>> #include <linux/verification.h>
>> #include <crypto/public_key.h>
>> #include "module-internal.h"
>>
>> -enum pkey_id_type {
>> - PKEY_ID_PGP, /* OpenPGP generated key ID */
>> - PKEY_ID_X509, /* X.509 arbitrary subjectKeyIdentifier */
>> - PKEY_ID_PKCS7, /* Signature in PKCS#7 message */
>> -};
>> -
>> -/*
>> - * Module signature information block.
>> - *
>> - * The constituents of the signature section are, in order:
>> +/**
>> + * validate_module_sig - validate that the given signature is sane
>> *
>> - * - Signer's name
>> - * - Key identifier
>> - * - Signature data
>> - * - Information block
>> + * @ms: Signature to validate.
>> + * @file_len: Size of the file to which @ms is appended.
>> */
>> -struct module_signature {
>> - u8 algo; /* Public-key crypto algorithm [0] */
>> - u8 hash; /* Digest algorithm [0] */
>> - u8 id_type; /* Key identifier type [PKEY_ID_PKCS7] */
>> - u8 signer_len; /* Length of signer's name [0] */
>> - u8 key_id_len; /* Length of key identifier [0] */
>> - u8 __pad[3];
>> - __be32 sig_len; /* Length of signature data */
>> -};
>> +int validate_module_sig(const struct module_signature *ms, size_t file_len)
>> +{
>> + if (be32_to_cpu(ms->sig_len) >= file_len - sizeof(*ms))
>> + return -EBADMSG;
>> + else if (ms->id_type != PKEY_ID_PKCS7) {
>> + pr_err("Module is not signed with expected PKCS#7 message\n");
>> + return -ENOPKG;
>> + } else if (ms->algo != 0 ||
>> + ms->hash != 0 ||
>> + ms->signer_len != 0 ||
>> + ms->key_id_len != 0 ||
>> + ms->__pad[0] != 0 ||
>> + ms->__pad[1] != 0 ||
>> + ms->__pad[2] != 0) {
>> + pr_err("PKCS#7 signature info has unexpected non-zero params\n");
>> + return -EBADMSG;
>> + }
>> +
>
> When moving code from one place to another, it's easier to review when
> there aren't code changes as well. In this case, the original code
> doesn't have "else clauses".

Indeed. I changed the code back to using separate if clauses, making
only the changes that are required for the refactoring.

> Here some of the if/then/else clauses
> have braces others don't. There shouldn't be a mixture.

Does this still apply when the if clauses are separate as in the
original code? Should the first if still have braces?

--
Thiago Jung Bauermann
IBM Linux Technology Center