security: introduce kernel_module_from_file hook

Now that kernel module origins can be reasoned about, provide a hook to
the LSMs to make policy decisions about the module file. This will let
Chrome OS enforce that loadable kernel modules can only come from its
read-only hash-verified root filesystem. Other LSMs can, for example,
read extended attributes for signatures, etc.

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Acked-by: Eric Paris <eparis@redhat.com>
Acked-by: Mimi Zohar <zohar@us.ibm.com>
Acked-by: James Morris <james.l.morris@oracle.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/include/linux/security.h b/include/linux/security.h
index 05e88bdcf7d95cbe493bfa8ed890010bd0094890..0f6afc657f778f2e682e7fb108e97b6788a53973 100644 (file)
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -694,6 +694,12 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
  *     userspace to load a kernel module with the given name.
  *     @kmod_name name of the module requested by the kernel
  *     Return 0 if successful.
+ * @kernel_module_from_file:
+ *     Load a kernel module from userspace.
+ *     @file contains the file structure pointing to the file containing
+ *     the kernel module to load. If the module is being loaded from a blob,
+ *     this argument will be NULL.
+ *     Return 0 if permission is granted.
  * @task_fix_setuid:
  *     Update the module's state after setting one or more of the user
  *     identity attributes of the current process.  The @flags parameter
@@ -1508,6 +1514,7 @@ struct security_operations {
        int (*kernel_act_as)(struct cred *new, u32 secid);
        int (*kernel_create_files_as)(struct cred *new, struct inode *inode);
        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,
                                int flags);
        int (*task_setpgid) (struct task_struct *p, pid_t pgid);
@@ -1765,6 +1772,7 @@ 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_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,
                             int flags);
 int security_task_setpgid(struct task_struct *p, pid_t pgid);
@@ -2278,6 +2286,11 @@ static inline int security_kernel_module_request(char *kmod_name)
        return 0;
 }
 
+static inline int security_kernel_module_from_file(struct file *file)
+{
+       return 0;
+}
+
 static inline int security_task_fix_setuid(struct cred *new,
                                           const struct cred *old,
                                           int flags)

diff --git a/kernel/module.c b/kernel/module.c
index 1395ca382fb51ffac1728a7716645799417d743b..a1d2ed8bab9322973be382bd311f6694e66f4c51 100644 (file)
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -29,6 +29,7 @@
 #include <linux/vmalloc.h>
 #include <linux/elf.h>
 #include <linux/proc_fs.h>
+#include <linux/security.h>
 #include <linux/seq_file.h>
 #include <linux/syscalls.h>
 #include <linux/fcntl.h>
@@ -2485,10 +2486,16 @@ static int elf_header_check(struct load_info *info)
 static int copy_module_from_user(const void __user *umod, unsigned long len,
                                  struct load_info *info)
 {
+       int err;
+
        info->len = len;
        if (info->len < sizeof(*(info->hdr)))
                return -ENOEXEC;
 
+       err = security_kernel_module_from_file(NULL);
+       if (err)
+               return err;
+
        /* Suck in entire file: we'll want most of it. */
        info->hdr = vmalloc(info->len);
        if (!info->hdr)
@@ -2515,6 +2522,10 @@ static int copy_module_from_fd(int fd, struct load_info *info)
        if (!file)
                return -ENOEXEC;
 
+       err = security_kernel_module_from_file(file);
+       if (err)
+               goto out;
+
        err = vfs_getattr(file->f_vfsmnt, file->f_dentry, &stat);
        if (err)
                goto out;

diff --git a/security/capability.c b/security/capability.c
index b14a30c234b885199fd6f8dac080a343255a7d1f..0fe5a026aef8d22ac83619dd0bbc2ba50965b63e 100644 (file)
--- a/security/capability.c
+++ b/security/capability.c
@@ -395,6 +395,11 @@ static int cap_kernel_module_request(char *kmod_name)
        return 0;
 }
 
+static int cap_kernel_module_from_file(struct file *file)
+{
+       return 0;
+}
+
 static int cap_task_setpgid(struct task_struct *p, pid_t pgid)
 {
        return 0;
@@ -967,6 +972,7 @@ void __init security_fixup_ops(struct security_operations *ops)
        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_module_request);
+       set_to_cap_if_null(ops, kernel_module_from_file);
        set_to_cap_if_null(ops, task_fix_setuid);
        set_to_cap_if_null(ops, task_setpgid);
        set_to_cap_if_null(ops, task_getpgid);

diff --git a/security/security.c b/security/security.c
index 8dcd4ae10a5fba06086ed31998c78c77ec32469c..ce88630de15d7f0b92ca03443d2627e85c87e166 100644 (file)
--- a/security/security.c
+++ b/security/security.c
@@ -820,6 +820,11 @@ int security_kernel_module_request(char *kmod_name)
        return security_ops->kernel_module_request(kmod_name);
 }
 
+int security_kernel_module_from_file(struct file *file)
+{
+       return security_ops->kernel_module_from_file(file);
+}
+
 int security_task_fix_setuid(struct cred *new, const struct cred *old,
                             int flags)
 {