[PATCH 3/7] security: introduce kernel_fw_from_file hook

Kees Cook
2014-07-14T21:38:41Z

In order to validate the contents of firmware being loaded, there must be
a hook to evaluate any loaded firmware that wasn't built into the kernel
itself. Without this, there is a risk that a root user could load malicious
firmware designed to mount an attack against kernel memory (e.g. via DMA).

Signed-off-by: Kees Cook <keescook@chromium.org>
---
include/linux/security.h | 16 ++++++++++++++++
security/capability.c | 6 ++++++
security/security.c | 6 ++++++
3 files changed, 28 insertions(+)

diff --git a/include/linux/security.h b/include/linux/security.h
index 9c6b9722ff48..dbb80b3e99d7 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -702,6 +702,14 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
* @inode points to the inode to use as a reference.
* The current task must be the one that nominated @inode.
* Return 0 if successful.
+ * @kernel_fw_from_file:
+ * Load firmware from userspace.
+ * @file contains the file structure pointing to the file containing
+ * the firmware to load. If the module is being loaded from a blob,
+ * this argument will be NULL.
+ * @buf pointer to buffer containing firmware contents.
+ * @size length of the firmware contents.
+ * Return 0 if permission is granted.
* @kernel_module_request:
* Ability to trigger the kernel to automatically upcall to userspace for
* userspace to load a kernel module with the given name.
@@ -1565,6 +1573,7 @@ struct security_operations {
void (*cred_transfer)(struct cred *new, const struct cred *old);
int (*kernel_act_as)(struct cred *new, u32 secid);
int (*kernel_create_files_as)(struct cred *new, struct inode *inode);
+ int (*kernel_fw_from_file)(struct file *file, char *buf, size_t size);
int (*kernel_module_request)(char *kmod_name);
int (*kernel_module_from_file)(struct file *file);
int (*task_fix_setuid) (struct cred *new, const struct cred *old,
@@ -1837,6 +1846,7 @@ int security_prepare_creds(struct cred *new, const struct cred *old, gfp_t gfp);
void security_transfer_creds(struct cred *new, const struct cred *old);
int security_kernel_act_as(struct cred *new, u32 secid);
int security_kernel_create_files_as(struct cred *new, struct inode *inode);
+int security_kernel_fw_from_file(struct file *file, char *buf, size_t size);
int security_kernel_module_request(char *kmod_name);
int security_kernel_module_from_file(struct file *file);
int security_task_fix_setuid(struct cred *new, const struct cred *old,
@@ -2363,6 +2373,12 @@ static inline int security_kernel_create_files_as(struct cred *cred,
return 0;
}

+static inline int security_kernel_fw_from_file(struct file *file,
+ char *buf, size_t size)
+{
+ return 0;
+}
+
static inline int security_kernel_module_request(char *kmod_name)
{
return 0;
diff --git a/security/capability.c b/security/capability.c
index e76373de3129..a74fde6a7468 100644
--- a/security/capability.c
+++ b/security/capability.c
@@ -401,6 +401,11 @@ static int cap_kernel_create_files_as(struct cred *new, struct inode *inode)
return 0;
}

+static int cap_kernel_fw_from_file(struct file *file, char *buf, size_t size)
+{
+ return 0;
+}
+
static int cap_kernel_module_request(char *kmod_name)
{
return 0;
@@ -1015,6 +1020,7 @@ void __init security_fixup_ops(struct security_operations *ops)
set_to_cap_if_null(ops, cred_transfer);
set_to_cap_if_null(ops, kernel_act_as);
set_to_cap_if_null(ops, kernel_create_files_as);
+ set_to_cap_if_null(ops, kernel_fw_from_file);
set_to_cap_if_null(ops, kernel_module_request);
set_to_cap_if_null(ops, kernel_module_from_file);
set_to_cap_if_null(ops, task_fix_setuid);
diff --git a/security/security.c b/security/security.c
index 31614e9e96e5..35d37d0f0d49 100644
--- a/security/security.c
+++ b/security/security.c
@@ -845,6 +845,12 @@ int security_kernel_create_files_as(struct cred *new, struct inode *inode)
return security_ops->kernel_create_files_as(new, inode);
}

+int security_kernel_fw_from_file(struct file *file, char *buf, size_t size)
+{
+ return security_ops->kernel_fw_from_file(file, buf, size);
+}
+EXPORT_SYMBOL_GPL(security_kernel_fw_from_file);
+
int security_kernel_module_request(char *kmod_name)
{
return security_ops->kernel_module_request(kmod_name);
--
1.7.9.5