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Date: Tue, 30 Oct 2012 14:11:13 -0700
From: Kees Cook <keescook@...omium.org>
To: David Howells <dhowells@...hat.com>
Cc: rusty@...tcorp.com.au, pjones@...hat.com, jwboyer@...hat.com,
mjg@...hat.com, dmitry.kasatkin@...el.com,
zohar@...ux.vnet.ibm.com, keyrings@...ux-nfs.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 16/23] pefile: Parse a PE binary to find a key and a
signature contained therein
On Tue, Oct 30, 2012 at 12:21 PM, David Howells <dhowells@...hat.com> wrote:
> Parse a PE binary to find a key and a signature contained therein. Later
> patches will check the signature and add the key if the signature checks out.
>
> Signed-off-by: David Howells <dhowells@...hat.com>
> ---
>
> crypto/asymmetric_keys/Kconfig | 10 ++
> crypto/asymmetric_keys/Makefile | 8 +
> crypto/asymmetric_keys/pefile_parser.c | 178 ++++++++++++++++++++++++++++++++
> crypto/asymmetric_keys/pefile_parser.h | 31 ++++++
> 4 files changed, 226 insertions(+), 1 deletion(-)
> create mode 100644 crypto/asymmetric_keys/pefile_parser.c
> create mode 100644 crypto/asymmetric_keys/pefile_parser.h
>
>
> diff --git a/crypto/asymmetric_keys/Kconfig b/crypto/asymmetric_keys/Kconfig
> index 413f3f6..2e7315c 100644
> --- a/crypto/asymmetric_keys/Kconfig
> +++ b/crypto/asymmetric_keys/Kconfig
> @@ -31,7 +31,7 @@ config X509_CERTIFICATE_PARSER
> select ASN1
> select OID_REGISTRY
> help
> - This option procides support for parsing X.509 format blobs for key
> + This option provides support for parsing X.509 format blobs for key
> data and provides the ability to instantiate a crypto key from a
> public key packet found inside the certificate.
>
> @@ -44,4 +44,12 @@ config PKCS7_MESSAGE_PARSER
> This option provides support for parsing PKCS#7 format messages for
> signature data and provides the ability to verify the signature.
>
> +config PE_FILE_PARSER
> + tristate "PE binary-wrapped key parser"
> + depends on X509_CERTIFICATE_PARSER
> + depends on PKCS7_MESSAGE_PARSER
> + help
> + This option provides support for parsing signed PE binaries that
> + contain an X.509 certificate in an internal section.
> +
> endif # ASYMMETRIC_KEY_TYPE
> diff --git a/crypto/asymmetric_keys/Makefile b/crypto/asymmetric_keys/Makefile
> index b6b39e7..61905d3 100644
> --- a/crypto/asymmetric_keys/Makefile
> +++ b/crypto/asymmetric_keys/Makefile
> @@ -39,3 +39,11 @@ $(obj)/pkcs7_parser.o: $(obj)/pkcs7-asn1.h
> $(obj)/pkcs7-asn1.o: $(obj)/pkcs7-asn1.c $(obj)/pkcs7-asn1.h
>
> clean-files += pkcs7-asn1.c pkcs7-asn1.h
> +
> +#
> +# Signed PE binary-wrapped key handling
> +#
> +obj-$(CONFIG_PE_FILE_PARSER) += pefile_key_parser.o
> +
> +pefile_key_parser-y := \
> + pefile_parser.o
> diff --git a/crypto/asymmetric_keys/pefile_parser.c b/crypto/asymmetric_keys/pefile_parser.c
> new file mode 100644
> index 0000000..efae278
> --- /dev/null
> +++ b/crypto/asymmetric_keys/pefile_parser.c
> @@ -0,0 +1,178 @@
> +/* Parse a signed PE binary that wraps a key.
> + *
> + * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells (dhowells@...hat.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.
> + */
> +
> +#define pr_fmt(fmt) "PEFILE: "fmt
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include <linux/slab.h>
> +#include <linux/err.h>
> +#include <linux/pe.h>
> +#include <keys/asymmetric-subtype.h>
> +#include <keys/asymmetric-parser.h>
> +#include <crypto/hash.h>
> +#include "asymmetric_keys.h"
> +#include "public_key.h"
> +#include "pefile_parser.h"
> +
> +/*
> + * Parse a PE binary.
> + */
> +static int pefile_parse_binary(struct key_preparsed_payload *prep,
> + struct pefile_context *ctx)
> +{
> + const struct mz_hdr *mz = prep->data;
> + const struct pe_hdr *pe;
> + const struct pe32_opt_hdr *pe32;
> + const struct pe32plus_opt_hdr *pe64;
> + const struct data_directory *ddir;
> + const struct data_dirent *dde;
> + const struct section_header *secs, *sec;
> + unsigned loop;
> + size_t cursor, datalen = prep->datalen;
> +
> + kenter("");
> +
> +#define chkaddr(base, x, s) \
> + do { \
> + if ((x) < base || (s) >= datalen || (x) > datalen - (s)) \
> + return -ERANGE; \
> + } while(0)
> +
> + chkaddr(0, 0, sizeof(*mz));
> + if (mz->magic != MZ_MAGIC)
> + return -ELIBBAD;
> + cursor = sizeof(*mz);
> +
> + chkaddr(cursor, mz->peaddr, sizeof(*pe));
> + pe = prep->data + mz->peaddr;
> + if (pe->magic != PE_MAGIC)
> + return -ELIBBAD;
> + cursor = mz->peaddr + sizeof(*pe);
> +
> + chkaddr(0, cursor, sizeof(pe32->magic));
> + pe32 = prep->data + cursor;
> + pe64 = prep->data + cursor;
> +
> + switch (pe32->magic) {
> + case PE_OPT_MAGIC_PE32:
> + chkaddr(0, cursor, sizeof(*pe32));
> + ctx->image_checksum_offset =
> + (unsigned long)&pe32->csum - (unsigned long)prep->data;
> + ctx->header_size = pe32->header_size;
> + cursor += sizeof(*pe32);
> + ctx->n_data_dirents = pe32->data_dirs;
> + break;
> +
> + case PE_OPT_MAGIC_PE32PLUS:
> + chkaddr(0, cursor, sizeof(*pe64));
> + ctx->image_checksum_offset =
> + (unsigned long)&pe64->csum - (unsigned long)prep->data;
> + ctx->header_size = pe64->header_size;
> + cursor += sizeof(*pe64);
> + ctx->n_data_dirents = pe64->data_dirs;
> + break;
> +
> + default:
> + pr_devel("Unknown PEOPT magic = %04hx\n", pe32->magic);
> + return -ELIBBAD;
> + }
> +
> + pr_devel("checksum @ %x\n", ctx->image_checksum_offset);
> + pr_devel("header size = %x\n", ctx->header_size);
> +
> + chkaddr(0, cursor, sizeof(*ddir));
> + ddir = prep->data + cursor;
> + cursor += sizeof(*dde) * ctx->n_data_dirents;
This multiplication can push the cursor out of bounds. (n_data_dirents
is unverified).
> + ctx->cert_dirent_offset =
> + (unsigned long)&ddir->certs - (unsigned long)prep->data;
> + ctx->certs_size = ddir->certs.size;
> +
> + if (!ddir->certs.virtual_address || !ddir->certs.size) {
> + pr_devel("Unsigned PE binary\n");
> + return -EKEYREJECTED;
> + }
> +
> + chkaddr(cursor, ddir->certs.virtual_address, ddir->certs.size);
> + ctx->sig_offset = ddir->certs.virtual_address;
> + ctx->sig_len = ddir->certs.size;
> + pr_devel("cert = %x @%x [%*ph]\n",
> + ctx->sig_len, ctx->sig_offset,
> + ctx->sig_len, prep->data + ctx->sig_offset);
> +
> + /* Parse the section table, checking the parameters and looking for the
> + * section containing the list of keys.
> + */
> + ctx->n_sections = pe->sections;
> + chkaddr(0, cursor, sizeof(*sec) * ctx->n_sections);
> + ctx->secs = secs = prep->data + cursor;
> + cursor += sizeof(*sec) * ctx->n_sections;
Both of these cases of n_sections multiplications can wrap.
Ultimately, you can end up with cursor close to zero, but n_sections
being giant.
> + for (loop = 0; loop < ctx->n_sections; loop++) {
> + sec = &secs[loop];
> + chkaddr(cursor, sec->data_addr, sec->raw_data_size);
> + if (memcmp(sec->name, ".keylist", 8) == 0) {
> + ctx->keylist_offset = sec->data_addr;
> + ctx->keylist_len = sec->raw_data_size;
> + }
> + }
Which means this loop will walk past the end of the memory (loop is
bounded by n_sections, so secs[loop] can go past datalen). While
data_addr and raw_data_size will stay bounded, the read of sec->name
can be out of bounds. (Also, do you want a "break" in there after the
first .keylist is found, or is this intentionally "use last key
list"?)
> +
> + if (ctx->keylist_offset == 0) {
> + pr_devel("No .keylist section in PE binary\n");
> + return -ENOENT;
> + }
> +
> + pr_devel("keylist = %x @%x [%*ph]\n",
> + ctx->keylist_len, ctx->keylist_offset,
> + ctx->keylist_len, prep->data + ctx->keylist_offset);
> +
> + return 0;
> +}
> +
> +/*
> + * Parse a PE binary.
> + */
> +static int pefile_key_preparse(struct key_preparsed_payload *prep)
> +{
> + struct pefile_context ctx;
> + int ret;
> +
> + kenter("");
> +
> + memset(&ctx, 0, sizeof(ctx));
> + ret = pefile_parse_binary(prep, &ctx);
> + if (ret < 0)
> + return ret;
> +
> + return -ENOANO; // Not yet complete
> +}
> +
> +static struct asymmetric_key_parser pefile_key_parser = {
> + .owner = THIS_MODULE,
> + .name = "pefile",
> + .parse = pefile_key_preparse,
> +};
> +
> +/*
> + * Module stuff
> + */
> +static int __init pefile_key_init(void)
> +{
> + return register_asymmetric_key_parser(&pefile_key_parser);
> +}
> +
> +static void __exit pefile_key_exit(void)
> +{
> + unregister_asymmetric_key_parser(&pefile_key_parser);
> +}
> +
> +module_init(pefile_key_init);
> +module_exit(pefile_key_exit);
> diff --git a/crypto/asymmetric_keys/pefile_parser.h b/crypto/asymmetric_keys/pefile_parser.h
> new file mode 100644
> index 0000000..82bcaf6
> --- /dev/null
> +++ b/crypto/asymmetric_keys/pefile_parser.h
> @@ -0,0 +1,31 @@
> +/* PE Binary parser bits
> + *
> + * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
> + * Written by David Howells (dhowells@...hat.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.
> + */
> +#include "pkcs7_parser.h"
> +
> +struct pefile_context {
> + unsigned header_size;
> + unsigned image_checksum_offset;
> + unsigned cert_dirent_offset;
> + unsigned n_data_dirents;
> + unsigned n_sections;
> + unsigned certs_size;
> + unsigned sig_offset;
> + unsigned sig_len;
> + unsigned keylist_offset;
> + unsigned keylist_len;
> + const struct section_header *secs;
> + struct pkcs7_message *pkcs7;
> +
> + /* PKCS#7 MS Individual Code Signing content */
> + const void *digest; /* Digest */
> + unsigned digest_len; /* Digest length */
> + enum pkey_hash_algo digest_algo; /* Digest algorithm */
> +};
>
--
Kees Cook
Chrome OS Security
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