[PATCH 2/5] IMA: Define an IMA hook to measure LSM data

Lakshmi Ramasubramanian
2020-06-13T02:41:54Z

LSM requires an IMA hook to be defined by the IMA subsystem to measure
the data gathered from the security modules.

Define a new IMA hook, namely ima_lsm_state(), that the LSM will call
to measure the data gathered from the security modules.

Sample IMA log entry for LSM measurement:

10 47eed9... ima-buf sha256:402f6b... lsm-state:selinux 656e61626c65643d313b656e666f7263696e673d30

Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
---
include/linux/ima.h | 4 ++++
security/integrity/ima/ima_main.c | 30 ++++++++++++++++++++++++++++++
2 files changed, 34 insertions(+)

diff --git a/include/linux/ima.h b/include/linux/ima.h
index 9164e1534ec9..56681a648b3d 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -26,6 +26,7 @@ extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
extern void ima_post_path_mknod(struct dentry *dentry);
extern int ima_file_hash(struct file *file, char *buf, size_t buf_size);
extern void ima_kexec_cmdline(const void *buf, int size);
+extern void ima_lsm_state(const char *lsm_name, const void *buf, int size);

#ifdef CONFIG_IMA_KEXEC
extern void ima_add_kexec_buffer(struct kimage *image);
@@ -104,6 +105,9 @@ static inline int ima_file_hash(struct file *file, char *buf, size_t buf_size)
}

static inline void ima_kexec_cmdline(const void *buf, int size) {}
+
+static inline void ima_lsm_state(const char *lsm_name,
+ const void *buf, int size) {}
#endif /* CONFIG_IMA */

#ifndef CONFIG_IMA_KEXEC
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index c1583d98c5e5..34be962054fb 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -827,6 +827,36 @@ void ima_kexec_cmdline(const void *buf, int size)
KEXEC_CMDLINE, 0, NULL);
}

+/**
+ * ima_lsm_state - measure LSM specific state
+ * @lsm_name: Name of the LSM
+ * @buf: pointer to buffer containing LSM specific state
+ * @size: Number of bytes in buf
+ *
+ * Buffers can only be measured, not appraised.
+ */
+void ima_lsm_state(const char *lsm_name, const void *buf, int size)
+{
+ const char *eventname = "lsm-state:";
+ char *lsmstatestring;
+ int lsmstatelen;
+
+ if (!lsm_name || !buf || !size)
+ return;
+
+ lsmstatelen = strlen(eventname) + strlen(lsm_name) + 1;
+ lsmstatestring = kzalloc(lsmstatelen, GFP_KERNEL);
+ if (!lsmstatestring)
+ return;
+
+ strcpy(lsmstatestring, eventname);
+ strcat(lsmstatestring, lsm_name);
+
+ process_buffer_measurement(buf, size, lsmstatestring,
+ LSM_STATE, 0, NULL);
+ kfree(lsmstatestring);
+}
+
static int __init init_ima(void)
{
int error;
--
2.27.0