[PATCH v3 6/7] ima-evm-utils: Extract digest algorithms from hash_info.h

[Vitaly Chikunov <vt@altlinux.org>]

If configured with "--with-kernel-headers=PATH" try to extract hash
algorithms from "hash_info.h" from the kernel source tree or
kernel-headers package located in the specified path. (Otherwise, it
will be tried to get from the installed kernel.)

This also introduces two algorithm lists, one is built-in and another is
from the kernel source. (They should never contain conflicting algorithm
IDs by their append-only nature.) If the digest is not found in the
built-in list it will be searched in the list from kernel's
"hash_info.h".

This patch will allow evmctl to be just recompiled to work with digest
algorithms introduced in the newer kernels.

Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
---
Changes since v1:
- New patch.
Changes since v2:
- Update commit description.
- Update description of --with-kernel-headers.

 configure.ac      |  6 ++++++
 src/Makefile.am   |  6 ++++++
 src/hash_info.gen | 43 +++++++++++++++++++++++++++++++++++++++++++
 src/libimaevm.c   | 44 +++++++++++++++++++++++++++++++++++++++++++-
 4 files changed, 98 insertions(+), 1 deletion(-)
 create mode 100755 src/hash_info.gen

diff --git a/configure.ac b/configure.ac
index a5b4288..60f3684 100644
--- a/configure.ac
+++ b/configure.ac
@@ -27,12 +27,18 @@ AC_HEADER_STDC
 PKG_CHECK_MODULES(OPENSSL, [ openssl >= 0.9.8 ])
 AC_SUBST(OPENSSL_CFLAGS)
 AC_SUBST(OPENSSL_LIBS)
+AC_SUBST(KERNEL_HEADERS)
 AC_CHECK_HEADER(unistd.h)
 AC_CHECK_HEADERS(openssl/conf.h)
 
 AC_CHECK_HEADERS(sys/xattr.h, , [AC_MSG_ERROR([sys/xattr.h header not found. You need the c-library development package.])])
 AC_CHECK_HEADERS(keyutils.h, , [AC_MSG_ERROR([keyutils.h header not found. You need the libkeyutils development package.])])
 
+AC_ARG_WITH(kernel_headers, [AS_HELP_STRING([--with-kernel-headers=PATH],
+	    [specifies the Linux kernel-headers package location or kernel root directory you want to use])],
+	    [KERNEL_HEADERS="$withval"],
+	    [KERNEL_HEADERS=/lib/modules/$(uname -r)/source])
+
 #debug support - yes for a while
 PKG_ARG_ENABLE(debug, "yes", DEBUG, [Enable Debug support])
 if test $pkg_cv_enable_debug = yes; then
diff --git a/src/Makefile.am b/src/Makefile.am
index deb18fb..d74fc6f 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -9,6 +9,11 @@ libimaevm_la_LIBADD =  $(OPENSSL_LIBS)
 
 include_HEADERS = imaevm.h
 
+nodist_libimaevm_la_SOURCES = hash_info.h
+BUILT_SOURCES = hash_info.h
+hash_info.h: Makefile
+	./hash_info.gen $(KERNEL_HEADERS) >$@
+
 bin_PROGRAMS = evmctl
 
 evmctl_SOURCES = evmctl.c
@@ -18,5 +23,6 @@ evmctl_LDADD =  $(OPENSSL_LIBS) -lkeyutils libimaevm.la
 
 INCLUDES = -I$(top_srcdir) -include config.h
 
+CLEANFILES = hash_info.h
 DISTCLEANFILES = @DISTCLEANFILES@
 
diff --git a/src/hash_info.gen b/src/hash_info.gen
new file mode 100755
index 0000000..60fc750
--- /dev/null
+++ b/src/hash_info.gen
@@ -0,0 +1,43 @@
+#!/bin/sh
+#
+# Generate hash_info.h from kernel headers
+#
+# Copyright (C) 2018 <vt@altlinux.org>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2, or (at your option)
+# any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+KERNEL_HEADERS=$1
+HASH_INFO_H=uapi/linux/hash_info.h
+HASH_INFO=$KERNEL_HEADERS/include/$HASH_INFO_H
+
+# Allow to specify kernel-headers past include/
+if [ ! -e $HASH_INFO ]; then
+  HASH_INFO2=$KERNEL_HEADERS/$HASH_INFO_H
+  if [ -e $HASH_INFO2 ]; then
+    HASH_INFO=$HASH_INFO2
+  fi
+fi
+
+if [ ! -e $HASH_INFO ]; then
+  echo "/* $HASH_INFO is not found */"
+  HASH_INFO=/dev/null
+else
+  echo "/* $HASH_INFO is found */"
+fi
+
+echo "enum hash_algo {"
+grep HASH_ALGO_.*, $HASH_INFO
+printf "\tHASH_ALGO__LAST\n"
+echo "};"
+
+echo "const char *const hash_algo_name[HASH_ALGO__LAST] = {"
+sed -n 's/HASH_ALGO_\(.*\),/[HASH_ALGO_\1] = "\L\1\E",/p' $HASH_INFO
+echo "};"
diff --git a/src/libimaevm.c b/src/libimaevm.c
index 7b2b62c..cb4721b 100644
--- a/src/libimaevm.c
+++ b/src/libimaevm.c
@@ -50,6 +50,7 @@
 #include <string.h>
 #include <stdio.h>
 #include <assert.h>
+#include <ctype.h>
 
 #include <openssl/crypto.h>
 #include <openssl/pem.h>
@@ -58,6 +59,7 @@
 #include <openssl/err.h>
 
 #include "imaevm.h"
+#include "hash_info.h"
 
 const char *const pkey_hash_algo[PKEY_HASH__LAST] = {
 	[PKEY_HASH_MD4]		= "md4",
@@ -153,6 +155,17 @@ void dump(const void *ptr, int len)
 	do_dump(stdout, ptr, len, true);
 }
 
+const char *get_hash_algo_by_id(int algo)
+{
+	if (algo < PKEY_HASH__LAST)
+	    return pkey_hash_algo[algo];
+	if (algo < HASH_ALGO__LAST)
+	    return hash_algo_name[algo];
+
+	log_err("digest %d not found\n", algo);
+	return "unknown";
+}
+
 int get_filesize(const char *filename)
 {
 	struct stat stats;
@@ -528,15 +541,44 @@ int verify_hash_v2(const char *file, const unsigned char *hash, int size,
 	return 0;
 }
 
+/* compare algo names case insensitively and ignoring separators */
+static int algocmp(const char *a, const char *b)
+{
+	while (*a && *b) {
+		int cha, chb;
+
+		cha = tolower((unsigned char)*a++);
+		if (!isalnum(cha))
+			continue;
+		chb = tolower((unsigned char)*b++);
+		if (!isalnum(chb)) {
+			a--;
+			continue;
+		}
+		if (cha != chb)
+			return -1;
+	}
+	return *a || *b;
+}
+
 int get_hash_algo(const char *algo)
 {
 	int i;
 
+	/* first iterate over builtin algorithms */
 	for (i = 0; i < PKEY_HASH__LAST; i++)
 		if (pkey_hash_algo[i] &&
 		    !strcmp(algo, pkey_hash_algo[i]))
 			return i;
 
+	/* iterate over algorithms provided by kernel-headers */
+	for (i = 0; i < HASH_ALGO__LAST; i++) {
+		if (hash_algo_name[i] &&
+		    !algocmp(algo, hash_algo_name[i]))
+			return i;
+	}
+
+	log_info("digest %s not found, fall back to sha1\n", algo);
 	return PKEY_HASH_SHA1;
 }
 
@@ -611,7 +653,7 @@ int ima_verify_signature(const char *file, unsigned char *sig, int siglen,
 		return -1;
 	}
 	/* Use hash algorithm as retrieved from signature */
-	params.hash_algo = pkey_hash_algo[sig_hash_algo];
+	params.hash_algo = get_hash_algo_by_id(sig_hash_algo);
 
 	/*
 	 * Validate the signature based on the digest included in the
-- 
2.11.0