[PATCH 5.15 697/731] LoadPin: Ignore the "contents" argument of the LSM hooks

Greg Kroah-Hartman
2022-12-28T16:00:26Z

From: Kees Cook <keescook@chromium.org>

[ Upstream commit 1a17e5b513ceebf21100027745b8731b4728edf7 ]

LoadPin only enforces the read-only origin of kernel file reads. Whether
or not it was a partial read isn't important. Remove the overly
conservative checks so that things like partial firmware reads will
succeed (i.e. reading a firmware header).

Fixes: 2039bda1fa8d ("LSM: Add "contents" flag to kernel_read_file hook")
Cc: Paul Moore <paul@paul-moore.com>
Cc: James Morris <jmorris@namei.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: linux-security-module@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Serge Hallyn <serge@hallyn.com>
Tested-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://lore.kernel.org/r/20221209195453.never.494-kees@kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
security/loadpin/loadpin.c | 30 ++++++++++++++++++------------
1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c
index b12f7d986b1e..5fce105a372d 100644
--- a/security/loadpin/loadpin.c
+++ b/security/loadpin/loadpin.c
@@ -118,21 +118,11 @@ static void loadpin_sb_free_security(struct super_block *mnt_sb)
}
}

-static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
- bool contents)
+static int loadpin_check(struct file *file, enum kernel_read_file_id id)
{
struct super_block *load_root;
const char *origin = kernel_read_file_id_str(id);

- /*
- * If we will not know that we'll be seeing the full contents
- * then we cannot trust a load will be complete and unchanged
- * off disk. Treat all contents=false hooks as if there were
- * no associated file struct.
- */
- if (!contents)
- file = NULL;
-
/* If the file id is excluded, ignore the pinning. */
if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
ignore_read_file_id[id]) {
@@ -187,9 +177,25 @@ static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
return 0;
}

+static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
+ bool contents)
+{
+ /*
+ * LoadPin only cares about the _origin_ of a file, not its
+ * contents, so we can ignore the "are full contents available"
+ * argument here.
+ */
+ return loadpin_check(file, id);
+}
+
static int loadpin_load_data(enum kernel_load_data_id id, bool contents)
{
- return loadpin_read_file(NULL, (enum kernel_read_file_id) id, contents);
+ /*
+ * LoadPin only cares about the _origin_ of a file, not its
+ * contents, so a NULL file is passed, and we can ignore the
+ * state of "contents".
+ */
+ return loadpin_check(NULL, (enum kernel_read_file_id) id);
}

static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
--
2.35.1