[PATCH 2/3] kexec: call LSM hook for kexec_load syscall

Mimi Zohar
2018-05-11T01:37:08Z

In order for LSMs and IMA-appraisal to differentiate between the
kexec_load and kexec_file_load_syscalls, an LSM call needs to be added
to the original kexec_load syscall. From a technical perspective there
is no need for defining a new LSM hook, as the existing
security_kernel_kexec_load() works just fine. However, the name is
confusing. For this reason, instead of defining a new LSM hook, this
patch defines security_kexec_load() as a wrapper for the existing LSM
security_kernel_file_read() hook.

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Matthew Garrett <mjg59@google.com>
Cc: Casey Schaufler <casey@schaufler-ca.com>

Changelog v1:
- Define and call security_kexec_load(), a wrapper for
security_kernel_read_file().
---
include/linux/security.h | 6 ++++++
kernel/kexec.c | 11 +++++++++++
security/security.c | 6 ++++++
3 files changed, 23 insertions(+)

diff --git a/include/linux/security.h b/include/linux/security.h
index 63030c85ee19..26f6d85903ed 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -323,6 +323,7 @@ int security_kernel_module_request(char *kmod_name);
int security_kernel_read_file(struct file *file, enum kernel_read_file_id id);
int security_kernel_post_read_file(struct file *file, char *buf, loff_t size,
enum kernel_read_file_id id);
+int security_kexec_load(void);
int security_task_fix_setuid(struct cred *new, const struct cred *old,
int flags);
int security_task_setpgid(struct task_struct *p, pid_t pgid);
@@ -922,6 +923,11 @@ static inline int security_kernel_post_read_file(struct file *file,
return 0;
}

+static inline int security_kexec_load(void)
+{
+ return 0;
+}
+
static inline int security_task_fix_setuid(struct cred *new,
const struct cred *old,
int flags)
diff --git a/kernel/kexec.c b/kernel/kexec.c
index aed8fb2564b3..6b44b0e9a60b 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -11,6 +11,7 @@
#include <linux/capability.h>
#include <linux/mm.h>
#include <linux/file.h>
+#include <linux/security.h>
#include <linux/kexec.h>
#include <linux/mutex.h>
#include <linux/list.h>
@@ -195,11 +196,21 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
static inline int kexec_load_check(unsigned long nr_segments,
unsigned long flags)
{
+ int result;
+
/* We only trust the superuser with rebooting the system. */
if (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
return -EPERM;

/*
+ * Allow LSMs and IMA to differentiate between kexec_load and
+ * kexec_file_load syscalls.
+ */
+ result = security_kexec_load();
+ if (result < 0)
+ return result;
+
+ /*
* Verify we have a legal set of flags
* This leaves us room for future extensions.
*/
diff --git a/security/security.c b/security/security.c
index 68f46d849abe..0f3390000156 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1044,6 +1044,12 @@ int security_kernel_read_file(struct file *file, enum kernel_read_file_id id)
}
EXPORT_SYMBOL_GPL(security_kernel_read_file);

+int security_kexec_load()
+{
+ return security_kernel_read_file(NULL, READING_KEXEC_IMAGE);
+}
+EXPORT_SYMBOL_GPL(security_kexec_load);
+
int security_kernel_post_read_file(struct file *file, char *buf, loff_t size,
enum kernel_read_file_id id)
{
--
2.7.5