LoadPin: Ignore the "contents" argument of the LSM hooks

[ 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>

diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c
index de41621..110a5ab 100644 (file)
--- a/security/loadpin/loadpin.c
+++ b/security/loadpin/loadpin.c
@@ -122,21 +122,11 @@ 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]) {
@@ -192,9 +182,25 @@ 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 = {