linux-kernel - [PATCH v3 1/3] ima: Introduce ima_get_current_hash

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Date:   Mon, 5 Jul 2021 11:09:20 +0200
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     <zohar@...ux.ibm.com>, <paul@...l-moore.com>
CC:     <stephen.smalley.work@...il.com>, <prsriva02@...il.com>,
        <tusharsu@...ux.microsoft.com>, <nramas@...ux.microsoft.com>,
        <linux-integrity@...r.kernel.org>,
        <linux-security-module@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <selinux@...r.kernel.org>,
        Roberto Sassu <roberto.sassu@...wei.com>
Subject: [PATCH v3 1/3] ima: Introduce ima_get_current_hash_algo()

This patch introduces the new function ima_get_current_hash_algo(), that
callers in the other kernel subsystems might use to obtain the hash
algorithm selected by IMA.

Its primary use will be to determine which algorithm has been used to
calculate the digest written by ima_measure_critical_data() to the location
passed as a new parameter (in a subsequent patch).

Since the hash algorithm does not change after the IMA setup phase, there
is no risk of races (obtaining a digest calculated with a different
algorithm than the one returned).

Reviewed-by: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
---
 include/linux/ima.h               | 7 +++++++
 security/integrity/ima/ima_main.c | 5 +++++
 2 files changed, 12 insertions(+)

diff --git a/include/linux/ima.h b/include/linux/ima.h
index 61d5723ec303..81e830d01ced 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -11,9 +11,11 @@
 #include <linux/fs.h>
 #include <linux/security.h>
 #include <linux/kexec.h>
+#include <crypto/hash_info.h>
 struct linux_binprm;
 
 #ifdef CONFIG_IMA
+extern enum hash_algo ima_get_current_hash_algo(void);
 extern int ima_bprm_check(struct linux_binprm *bprm);
 extern int ima_file_check(struct file *file, int mask);
 extern void ima_post_create_tmpfile(struct user_namespace *mnt_userns,
@@ -64,6 +66,11 @@ static inline const char * const *arch_get_ima_policy(void)
 #endif
 
 #else
+static inline enum hash_algo ima_get_current_hash_algo(void)
+{
+	return HASH_ALGO__LAST;
+}
+
 static inline int ima_bprm_check(struct linux_binprm *bprm)
 {
 	return 0;
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 287b90509006..8ef1fa357e0c 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -76,6 +76,11 @@ static int __init hash_setup(char *str)
 }
 __setup("ima_hash=", hash_setup);
 
+enum hash_algo ima_get_current_hash_algo(void)
+{
+	return ima_hash_algo;
+}
+
 /* Prevent mmap'ing a file execute that is already mmap'ed write */
 static int mmap_violation_check(enum ima_hooks func, struct file *file,
 				char **pathbuf, const char **pathname,
-- 
2.25.1