ima: Introduce ima_get_current_hash_algo()

Buffer measurements, unlike file measurements, are not accessible after the
measurement is done, as buffers are not suitable for use with the
integrity_iint_cache structure (there is no index, for files it is the
inode number). In the subsequent patches, the measurement (digest) will be
returned directly by the functions that perform the buffer measurement,
ima_measure_critical_data() and process_buffer_measurement().

A caller of those functions also needs to know the algorithm used to
calculate the digest. Instead of adding the algorithm as a new parameter to
the functions, this patch provides it separately with the new function
ima_get_current_hash_algo().

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).

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
[zohar@linux.ibm.com: annotate ima_hash_algo as __ro_after_init]
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

1 files changed, 7 insertions, 0 deletions

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;