LoadPin: Annotate struct dm_verity_loadpin_trusted_root_digest with __counted_by

Prepare for the coming implementation by GCC and Clang of the __counted_by attribute. Flexible array members annotated with __counted_by can have their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family functions).

As found with Coccinelle[1], add __counted_by for struct dm_verity_loadpin_trusted_root_digest. Additionally, since the element count member must be set before accessing
the annotated flexible array member, move its initialization earlier.

[1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

---
 include/linux/dm-verity-loadpin.h | 2 +-
 security/loadpin/loadpin.c        | 3 +--
 2 files changed, 2 insertions(+), 3 deletions(-)

index 552b817ab102..3ac6dbaeaa37 100644
@@ -12,7 +12,7 @@ extern struct list_head dm_verity_loadpin_trusted_root_digests;
 struct dm_verity_loadpin_trusted_root_digest {
 	struct list_head node;
 	unsigned int len;
-	u8 data[];
+	u8 data[] __counted_by(len);
 };
 
 #if IS_ENABLED(CONFIG_SECURITY_LOADPIN_VERITY)

index ebae964f7cc9..a9d40456a064 100644
@@ -336,6 +336,7 @@ static int read_trusted_verity_root_digests(unsigned int fd)
 			rc = -ENOMEM;
 			goto err;
 		}
+		trd->len = len;
 
 		if (hex2bin(trd->data, d, len)) {
 			kfree(trd);

@@ -343,8 +344,6 @@ static int read_trusted_verity_root_digests(unsigned int fd)
 			goto err;
 		}
 
-		trd->len = len;
-
 		list_add_tail(&trd->node, &dm_verity_loadpin_trusted_root_digests);
 	}
 

2.34.1

Applied to for-next/hardening, thanks!

[1/1] LoadPin: Annotate struct dm_verity_loadpin_trusted_root_digest with __counted_by

      https://git.kernel.org/kees/c/5f536ac6a5a7

Take care,

Kees Cook