On Wed, Jul 29, 2020 at 7:59 PM Kees Cook keescook@chromium.org wrote:
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
Thanks for adding this! Would be really useful for us.
Reviewed-by: KP Singh kpsingh@google.com
drivers/base/firmware_loader/fallback.c | 2 +-
[...]
index 5de45010fb1a..1a5c68196faf 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -4019,7 +4019,7 @@ static int selinux_kernel_read_file(struct file *file, return rc; }
-static int selinux_kernel_load_data(enum kernel_load_data_id id) +static int selinux_kernel_load_data(enum kernel_load_data_id id, bool contents) { int rc = 0;
-- 2.25.1