LSM: Introduce kernel_post_load_data() hook

There are a few places in the kernel where LSMs would like to have
visibility into the contents of a kernel buffer that has been loaded or
read. While security_kernel_post_read_file() (which includes the
buffer) exists as a pairing for security_kernel_read_file(), no such
hook exists to pair with security_kernel_load_data().

Earlier proposals for just using security_kernel_post_read_file() with a
NULL file argument were rejected (i.e. "file" should always be valid for
the security_..._file hooks, but it appears at least one case was
left in the kernel during earlier refactoring. (This will be fixed in
a subsequent patch.)

Since not all cases of security_kernel_load_data() can have a single
contiguous buffer made available to the LSM hook (e.g. kexec image
segments are separately loaded), there needs to be a way for the LSM to
reason about its expectations of the hook coverage. In order to handle
this, add a "contents" argument to the "kernel_load_data" hook that
indicates if the newly added "kernel_post_load_data" hook will be called
with the full contents once loaded. That way, LSMs requiring full contents
can choose to unilaterally reject "kernel_load_data" with contents=false
(which is effectively the existing hook coverage), but when contents=true
they can allow it and later evaluate the "kernel_post_load_data" hook
once the buffer is loaded.

With this change, LSMs can gain coverage over non-file-backed data loads
(e.g. init_module(2) and firmware userspace helper), which will happen
in subsequent patches.

Additionally prepare IMA to start processing these cases.

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: KP Singh <kpsingh@google.com>
Link: https://lore.kernel.org/r/20201002173828.2099543-9-keescook@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

4 files changed, 36 insertions, 5 deletions

diff --git a/include/linux/ima.h b/include/linux/ima.h
index 64804f78408b..af9fb8c5f16a 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -20,7 +20,9 @@ extern void ima_post_create_tmpfile(struct inode *inode);
 extern void ima_file_free(struct file *file);
 extern int ima_file_mmap(struct file *file, unsigned long prot);
 extern int ima_file_mprotect(struct vm_area_struct *vma, unsigned long prot);
-extern int ima_load_data(enum kernel_load_data_id id);
+extern int ima_load_data(enum kernel_load_data_id id, bool contents);
+extern int ima_post_load_data(char *buf, loff_t size,
+			      enum kernel_load_data_id id, char *description);
 extern int ima_read_file(struct file *file, enum kernel_read_file_id id);
 extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
 			      enum kernel_read_file_id id);
@@ -78,7 +80,14 @@ static inline int ima_file_mprotect(struct vm_area_struct *vma,
 	return 0;
 }
 
-static inline int ima_load_data(enum kernel_load_data_id id)
+static inline int ima_load_data(enum kernel_load_data_id id, bool contents)
+{
+	return 0;
+}
+
+static inline int ima_post_load_data(char *buf, loff_t size,
+				     enum kernel_load_data_id id,
+				     char *description)
 {
 	return 0;
 }
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 2a8c74d99015..83c6f1f5cc1e 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -184,7 +184,9 @@ LSM_HOOK(void, LSM_RET_VOID, cred_getsecid, const struct cred *c, u32 *secid)
 LSM_HOOK(int, 0, kernel_act_as, struct cred *new, u32 secid)
 LSM_HOOK(int, 0, kernel_create_files_as, struct cred *new, struct inode *inode)
 LSM_HOOK(int, 0, kernel_module_request, char *kmod_name)
-LSM_HOOK(int, 0, kernel_load_data, enum kernel_load_data_id id)
+LSM_HOOK(int, 0, kernel_load_data, enum kernel_load_data_id id, bool contents)
+LSM_HOOK(int, 0, kernel_post_load_data, char *buf, loff_t size,
+	 enum kernel_read_file_id id, char *description)
 LSM_HOOK(int, 0, kernel_read_file, struct file *file,
 	 enum kernel_read_file_id id)
 LSM_HOOK(int, 0, kernel_post_read_file, struct file *file, char *buf,
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 9e2e3e63719d..6bb4f1a0158c 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -635,7 +635,17 @@
  * @kernel_load_data:
  *	Load data provided by userspace.
  *	@id kernel load data identifier
+ *	@contents if a subsequent @kernel_post_load_data will be called.
  *	Return 0 if permission is granted.
+ * @kernel_post_load_data:
+ *	Load data provided by a non-file source (usually userspace buffer).
+ *	@buf pointer to buffer containing the data contents.
+ *	@size length of the data contents.
+ *	@id kernel load data identifier
+ *	@description a text description of what was loaded, @id-specific
+ *	Return 0 if permission is granted.
+ *	This must be paired with a prior @kernel_load_data call that had
+ *	@contents set to true.
  * @kernel_read_file:
  *	Read a file specified by userspace.
  *	@file contains the file structure pointing to the file being read
diff --git a/include/linux/security.h b/include/linux/security.h
index 42df0d9b4c37..51c8e4e6b7cc 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -387,7 +387,10 @@ void security_cred_getsecid(const struct cred *c, u32 *secid);
 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_load_data(enum kernel_load_data_id id);
+int security_kernel_load_data(enum kernel_load_data_id id, bool contents);
+int security_kernel_post_load_data(char *buf, loff_t size,
+				   enum kernel_load_data_id id,
+				   char *description);
 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);
@@ -1014,7 +1017,14 @@ static inline int security_kernel_module_request(char *kmod_name)
 	return 0;
 }
 
-static inline int security_kernel_load_data(enum kernel_load_data_id id)
+static inline int security_kernel_load_data(enum kernel_load_data_id id, bool contents)
+{
+	return 0;
+}
+
+static inline int security_kernel_post_load_data(char *buf, loff_t size,
+						 enum kernel_load_data_id id,
+						 char *description)
 {
 	return 0;
 }