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

Mimi Zohar
2017-10-26T23:13:47Z

On Thu, 2017-10-26 at 20:47 -0200, Thiago Jung Bauermann wrote:
> 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?

No, the original code was fine.