[PATCH v3 0/2] security: introduce kernel_fw_from_file hook

[PATCH v3 0/2] security: introduce kernel_fw_from_file hook

[Kees Cook]

This adds an LSM hook to the existing firmware loading logic so that
the LSM can reason about the origin and contents of a firmware coming
from userspace.

Thanks,

-Kees

v3:
- correctly return LSM error to userspace (ming.lei)
- finalize memory map before calling LSM hook (tiwai)
v2:
- further clarify header comments (jmorris)

[PATCH v3 1/2] security: introduce kernel_fw_from_file hook

[Kees Cook]

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 |   17 +++++++++++++++++
 security/capability.c    |    6 ++++++
 security/security.c      |    6 ++++++
 3 files changed, 29 insertions(+)

diff --git a/include/linux/security.h b/include/linux/security.h
index 9c6b9722ff48..623f90e5f38d 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -702,6 +702,15 @@ 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 (not called for built-in firmware).
+ *	@file contains the file structure pointing to the file containing
+ *	the firmware to load. This argument will be NULL if the firmware
+ *	was loaded via the uevent-triggered blob-based interface exposed
+ *	by CONFIG_FW_LOADER_USER_HELPER.
+ *	@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 +1574,7 @@ 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 +1847,7 @@ 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 +2374,12 @@ 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

[PATCH v3 2/2] firmware_class: perform new LSM checks

[Kees Cook]

This attaches LSM hooks to the existing firmware loading interfaces:
filesystem-found firmware and demand-loaded blobs. On errors, loads
are aborted and the failure code is returned to userspace.

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/base/firmware_class.c |   30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index d276e33880be..63f165c59da8 100644
--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c
@@ -28,6 +28,7 @@
 #include <linux/suspend.h>
 #include <linux/syscore_ops.h>
 #include <linux/reboot.h>
+#include <linux/security.h>
 
 #include <generated/utsrelease.h>
 
@@ -308,12 +309,17 @@ static int fw_read_file_contents(struct file *file, struct firmware_buf *fw_buf)
 	if (rc != size) {
 		if (rc > 0)
 			rc = -EIO;
-		vfree(buf);
-		return rc;
+		goto fail;
 	}
+	rc = security_kernel_fw_from_file(file, buf, size);
+	if (rc)
+		goto fail;
 	fw_buf->data = buf;
 	fw_buf->size = size;
 	return 0;
+fail:
+	vfree(buf);
+	return rc;
 }
 
 static int fw_get_filesystem_firmware(struct device *device,
@@ -617,6 +623,7 @@ static ssize_t firmware_loading_store(struct device *dev,
 {
 	struct firmware_priv *fw_priv = to_firmware_priv(dev);
 	struct firmware_buf *fw_buf;
+	ssize_t written = count;
 	int loading = simple_strtol(buf, NULL, 10);
 	int i;
 
@@ -640,6 +647,8 @@ static ssize_t firmware_loading_store(struct device *dev,
 		break;
 	case 0:
 		if (test_bit(FW_STATUS_LOADING, &fw_buf->status)) {
+			int rc;
+
 			set_bit(FW_STATUS_DONE, &fw_buf->status);
 			clear_bit(FW_STATUS_LOADING, &fw_buf->status);
 
@@ -649,10 +658,23 @@ static ssize_t firmware_loading_store(struct device *dev,
 			 * see the mapped 'buf->data' once the loading
 			 * is completed.
 			 * */
-			if (fw_map_pages_buf(fw_buf))
+			rc = fw_map_pages_buf(fw_buf);
+			if (rc)
 				dev_err(dev, "%s: map pages failed\n",
 					__func__);
+			else
+				rc = security_kernel_fw_from_file(NULL,
+						fw_buf->data, fw_buf->size);
+
+			/*
+			 * Same logic as fw_load_abort, only the DONE bit
+			 * is ignored and we set ABORT only on failure.
+			 */
 			list_del_init(&fw_buf->pending_list);
+			if (rc) {
+				set_bit(FW_STATUS_ABORT, &fw_buf->status);
+				written = rc;
+			}
 			complete_all(&fw_buf->completion);
 			break;
 		}
@@ -666,7 +688,7 @@ static ssize_t firmware_loading_store(struct device *dev,
 	}
 out:
 	mutex_unlock(&fw_lock);
-	return count;
+	return written;
 }
 
 static DEVICE_ATTR(loading, 0644, firmware_loading_show, firmware_loading_store);
-- 
1.7.9.5

Re: [PATCH v3 0/2] security: introduce kernel_fw_from_file hook

[Takashi Iwai]

At Tue, 22 Jul 2014 11:28:59 -0700,
Kees Cook wrote:
n> 
> This adds an LSM hook to the existing firmware loading logic so that
> the LSM can reason about the origin and contents of a firmware coming
> from userspace.
> 
> Thanks,
> 
> -Kees
> 
> v3:
> - correctly return LSM error to userspace (ming.lei)
> - finalize memory map before calling LSM hook (tiwai)
> v2:
> - further clarify header comments (jmorris)

To both patches,
  Reviewed-by: Takashi Iwai <tiwai@suse.de>


thanks,

Takashi