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>

1 files changed, 17 insertions, 3 deletions

diff --git a/security/security.c b/security/security.c
index 19d3150f68f4..531b855826fc 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1695,17 +1695,31 @@ int security_kernel_post_read_file(struct file *file, char *buf, loff_t size,
 }
 EXPORT_SYMBOL_GPL(security_kernel_post_read_file);
 
-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 ret;
 
-	ret = call_int_hook(kernel_load_data, 0, id);
+	ret = call_int_hook(kernel_load_data, 0, id, contents);
 	if (ret)
 		return ret;
-	return ima_load_data(id);
+	return ima_load_data(id, contents);
 }
 EXPORT_SYMBOL_GPL(security_kernel_load_data);
 
+int security_kernel_post_load_data(char *buf, loff_t size,
+				   enum kernel_load_data_id id,
+				   char *description)
+{
+	int ret;
+
+	ret = call_int_hook(kernel_post_load_data, 0, buf, size, id,
+			    description);
+	if (ret)
+		return ret;
+	return ima_post_load_data(buf, size, id, description);
+}
+EXPORT_SYMBOL_GPL(security_kernel_post_load_data);
+
 int security_task_fix_setuid(struct cred *new, const struct cred *old,
 			     int flags)
 {