| Message ID | 1492546666-16615-6-git-send-email-bauerman@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Delegated to: | Herbert Xu |
| Headers | show |
On Tue, 2017-04-18 at 17:17 -0300, 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. Basically we want to generalize the concept of an appended signature. Referring to it as a "module signature format" seems a bit confusing. David, would you have a problem with changing the appended string from "~Module signature appended~\n" to something more generic? The appended signature format could be used by anything calling kernel_read_file() (eg. kexec kernel image/initramfs). Mimi > Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com> > --- > include/linux/module_signature.h | 45 ++++++++++++++++++++++++ > init/Kconfig | 6 +++- > kernel/Makefile | 2 +- > kernel/module_signing.c | 74 +++++++++++++++++----------------------- > 4 files changed, 82 insertions(+), 45 deletions(-) > > diff --git a/include/linux/module_signature.h b/include/linux/module_signature.h > new file mode 100644 > index 000000000000..b04f16559b47 > --- /dev/null > +++ b/include/linux/module_signature.h > @@ -0,0 +1,45 @@ > +/* Module signature handling. > + * > + * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved. > + * Written by David Howells (dhowells@redhat.com) > + * > + * This program is free software; you can redistribute it and/or > + * modify it under the terms of the GNU General Public Licence > + * as published by the Free Software Foundation; either version > + * 2 of the Licence, or (at your option) any later version. > + */ > + > +#ifndef _LINUX_MODULE_SIGNATURE_H > +#define _LINUX_MODULE_SIGNATURE_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: > + * > + * - Signer's name > + * - Key identifier > + * - Signature data > + * - Information block > + */ > +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_signature(const struct module_signature *ms, > + size_t file_len); > +int mod_verify_sig(const void *mod, unsigned long *_modlen); > + > +#endif /* _LINUX_MODULE_SIGNATURE_H */ > diff --git a/init/Kconfig b/init/Kconfig > index a92f27da4a27..891325e5aeff 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -2024,7 +2024,7 @@ config MODULE_SRCVERSION_ALL > config MODULE_SIG > bool "Module signature verification" > depends on MODULES > - select SYSTEM_DATA_VERIFICATION > + select MODULE_SIG_FORMAT > help > Check modules for valid signatures upon load: the signature > is simply appended to the module. For more information see > @@ -2039,6 +2039,10 @@ config MODULE_SIG > debuginfo strip done by some packagers (such as rpmbuild) and > inclusion into an initramfs that wants the module size reduced. > > +config MODULE_SIG_FORMAT > + def_bool n > + select SYSTEM_DATA_VERIFICATION > + > config MODULE_SIG_FORCE > bool "Require modules to be validly signed" > depends on MODULE_SIG > diff --git a/kernel/Makefile b/kernel/Makefile > index b302b4731d16..4451bbc70a08 100644 > --- a/kernel/Makefile > +++ b/kernel/Makefile > @@ -56,7 +56,7 @@ obj-y += up.o > endif > obj-$(CONFIG_UID16) += uid16.o > obj-$(CONFIG_MODULES) += module.o > -obj-$(CONFIG_MODULE_SIG) += module_signing.o > +obj-$(CONFIG_MODULE_SIG_FORMAT) += module_signing.o > obj-$(CONFIG_KALLSYMS) += kallsyms.o > obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o > obj-$(CONFIG_KEXEC_CORE) += kexec_core.o > diff --git a/kernel/module_signing.c b/kernel/module_signing.c > index 937c844bee4a..421e3e668714 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_signature - 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_signature(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; > + } > + > + return 0; > +} > > /* > * Verify the signature on a module. > @@ -49,6 +51,7 @@ int mod_verify_sig(const void *mod, unsigned long *_modlen) > { > struct module_signature ms; > size_t modlen = *_modlen, sig_len; > + int ret; > > pr_devel("==>%s(,%zu)\n", __func__, modlen); > > @@ -56,30 +59,15 @@ int mod_verify_sig(const void *mod, unsigned long *_modlen) > return -EBADMSG; > > memcpy(&ms, mod + (modlen - sizeof(ms)), sizeof(ms)); > - modlen -= sizeof(ms); > + > + ret = validate_module_signature(&ms, modlen); > + if (ret) > + return ret; > > sig_len = be32_to_cpu(ms.sig_len); > - if (sig_len >= modlen) > - return -EBADMSG; > - modlen -= sig_len; > + modlen -= sig_len + sizeof(ms); > *_modlen = modlen; > > - if (ms.id_type != PKEY_ID_PKCS7) { > - pr_err("Module is not signed with expected PKCS#7 message\n"); > - return -ENOPKG; > - } > - > - 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; > - } > - > return verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len, > NULL, VERIFYING_MODULE_SIGNATURE, > NULL, NULL);
Mimi Zohar <zohar@linux.vnet.ibm.com> wrote: > On Tue, 2017-04-18 at 17:17 -0300, 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. > > Basically we want to generalize the concept of an appended signature. > Referring to it as a "module signature format" seems a bit confusing. > > David, would you have a problem with changing the appended string from > "~Module signature appended~\n" to something more generic? Conceptually, no. Is it possible that doing so could break someone's module that they load on multiple versions of the kernel? Say a module that only exports things and doesn't use anything from the core or any other module. Also, it needs to reasonably long and distinct enough to prevent a false positive match. David
Am Donnerstag, 20. April 2017, 15:37:37 BRT schrieb David Howells: > Mimi Zohar <zohar@linux.vnet.ibm.com> wrote: > > On Tue, 2017-04-18 at 17:17 -0300, 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. > > > > Basically we want to generalize the concept of an appended signature. > > Referring to it as a "module signature format" seems a bit confusing. > > > > David, would you have a problem with changing the appended string from > > "~Module signature appended~\n" to something more generic? > > Conceptually, no. Is it possible that doing so could break someone's module > that they load on multiple versions of the kernel? Say a module that only > exports things and doesn't use anything from the core or any other module. I think that changing the appended string has limited value because very few people actually see them. It's just a marker. We could s/module_signature/ appended_signature/ in the code but keep the actual string unchanged. What do you think? Alternatively, we could change the string but accept both the old and the new string for backwards compatibility.
diff --git a/include/linux/module_signature.h b/include/linux/module_signature.h new file mode 100644 index 000000000000..b04f16559b47 --- /dev/null +++ b/include/linux/module_signature.h @@ -0,0 +1,45 @@ +/* Module signature handling. + * + * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved. + * Written by David Howells (dhowells@redhat.com) + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public Licence + * as published by the Free Software Foundation; either version + * 2 of the Licence, or (at your option) any later version. + */ + +#ifndef _LINUX_MODULE_SIGNATURE_H +#define _LINUX_MODULE_SIGNATURE_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: + * + * - Signer's name + * - Key identifier + * - Signature data + * - Information block + */ +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_signature(const struct module_signature *ms, + size_t file_len); +int mod_verify_sig(const void *mod, unsigned long *_modlen); + +#endif /* _LINUX_MODULE_SIGNATURE_H */ diff --git a/init/Kconfig b/init/Kconfig index a92f27da4a27..891325e5aeff 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -2024,7 +2024,7 @@ config MODULE_SRCVERSION_ALL config MODULE_SIG bool "Module signature verification" depends on MODULES - select SYSTEM_DATA_VERIFICATION + select MODULE_SIG_FORMAT help Check modules for valid signatures upon load: the signature is simply appended to the module. For more information see @@ -2039,6 +2039,10 @@ config MODULE_SIG debuginfo strip done by some packagers (such as rpmbuild) and inclusion into an initramfs that wants the module size reduced. +config MODULE_SIG_FORMAT + def_bool n + select SYSTEM_DATA_VERIFICATION + config MODULE_SIG_FORCE bool "Require modules to be validly signed" depends on MODULE_SIG diff --git a/kernel/Makefile b/kernel/Makefile index b302b4731d16..4451bbc70a08 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -56,7 +56,7 @@ obj-y += up.o endif obj-$(CONFIG_UID16) += uid16.o obj-$(CONFIG_MODULES) += module.o -obj-$(CONFIG_MODULE_SIG) += module_signing.o +obj-$(CONFIG_MODULE_SIG_FORMAT) += module_signing.o obj-$(CONFIG_KALLSYMS) += kallsyms.o obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o obj-$(CONFIG_KEXEC_CORE) += kexec_core.o diff --git a/kernel/module_signing.c b/kernel/module_signing.c index 937c844bee4a..421e3e668714 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_signature - 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_signature(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; + } + + return 0; +} /* * Verify the signature on a module. @@ -49,6 +51,7 @@ int mod_verify_sig(const void *mod, unsigned long *_modlen) { struct module_signature ms; size_t modlen = *_modlen, sig_len; + int ret; pr_devel("==>%s(,%zu)\n", __func__, modlen); @@ -56,30 +59,15 @@ int mod_verify_sig(const void *mod, unsigned long *_modlen) return -EBADMSG; memcpy(&ms, mod + (modlen - sizeof(ms)), sizeof(ms)); - modlen -= sizeof(ms); + + ret = validate_module_signature(&ms, modlen); + if (ret) + return ret; sig_len = be32_to_cpu(ms.sig_len); - if (sig_len >= modlen) - return -EBADMSG; - modlen -= sig_len; + modlen -= sig_len + sizeof(ms); *_modlen = modlen; - if (ms.id_type != PKEY_ID_PKCS7) { - pr_err("Module is not signed with expected PKCS#7 message\n"); - return -ENOPKG; - } - - 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; - } - return verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len, NULL, VERIFYING_MODULE_SIGNATURE, NULL, NULL);
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> --- include/linux/module_signature.h | 45 ++++++++++++++++++++++++ init/Kconfig | 6 +++- kernel/Makefile | 2 +- kernel/module_signing.c | 74 +++++++++++++++++----------------------- 4 files changed, 82 insertions(+), 45 deletions(-)