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

Cc: Alasdair Kergon <agk@redhat.com>
Cc: Mike Snitzer <snitzer@kernel.org>
Cc: dm-devel@redhat.com
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
Link: https://lore.kernel.org/r/20230817235955.never.762-kees@kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/include/linux/dm-verity-loadpin.h b/include/linux/dm-verity-loadpin.h
index 552b817ab102e29e7ac573bc28e32b6dacc62bb5..3ac6dbaeaa37b35057a59b81c0d4a299bffeb70d 100644 (file)
--- a/include/linux/dm-verity-loadpin.h
+++ b/include/linux/dm-verity-loadpin.h
@@ -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)

diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c
index ebae964f7cc9a47e020ef0f08f3f6139bd204f91..a9d40456a064579dbf6cef774410806efd62d890 100644 (file)
--- a/security/loadpin/loadpin.c
+++ b/security/loadpin/loadpin.c
@@ -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);
        }