ima: Return int in the functions to measure a buffer

ima_measure_critical_data() and process_buffer_measurement() currently
don't return a result as, unlike appraisal-related functions, the result is
not used by callers to deny an operation. Measurement-related functions
instead rely on the audit subsystem to notify the system administrator when
an error occurs.

However, ima_measure_critical_data() and process_buffer_measurement() are a
special case, as these are the only functions that can return a buffer
measurement (for files, there is ima_file_hash()). In a subsequent patch,
they will be modified to return the calculated digest.

In preparation to return the result of the digest calculation, this patch
modifies the return type from void to int, and returns 0 if the buffer has
been successfully measured, a negative value otherwise.

Given that the result of the measurement is still not necessary, this patch
does not modify the behavior of existing callers by processing the returned
value. For those, the return value is ignored.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Acked-by: Paul Moore <paul@paul-moore.com> (for the SELinux bits)
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

1 files changed, 9 insertions, 6 deletions

diff --git a/include/linux/ima.h b/include/linux/ima.h
index 81e830d01ced..60492263aa64 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -35,10 +35,10 @@ extern void ima_post_path_mknod(struct user_namespace *mnt_userns,
 extern int ima_file_hash(struct file *file, char *buf, size_t buf_size);
 extern int ima_inode_hash(struct inode *inode, char *buf, size_t buf_size);
 extern void ima_kexec_cmdline(int kernel_fd, const void *buf, int size);
-extern void ima_measure_critical_data(const char *event_label,
-				      const char *event_name,
-				      const void *buf, size_t buf_len,
-				      bool hash);
+extern int ima_measure_critical_data(const char *event_label,
+				     const char *event_name,
+				     const void *buf, size_t buf_len,
+				     bool hash);
 
 #ifdef CONFIG_IMA_APPRAISE_BOOTPARAM
 extern void ima_appraise_parse_cmdline(void);
@@ -144,10 +144,13 @@ static inline int ima_inode_hash(struct inode *inode, char *buf, size_t buf_size
 
 static inline void ima_kexec_cmdline(int kernel_fd, const void *buf, int size) {}
 
-static inline void ima_measure_critical_data(const char *event_label,
+static inline int ima_measure_critical_data(const char *event_label,
 					     const char *event_name,
 					     const void *buf, size_t buf_len,
-					     bool hash) {}
+					     bool hash)
+{
+	return -ENOENT;
+}
 
 #endif /* CONFIG_IMA */