[PATCH] selinux: Annotate struct sidtab_str_cache with __counted_by

[Kees Cook]

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 sidtab_str_cache.

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

Cc: Paul Moore <paul@xxxxxxxxxxxxxx>
Cc: Stephen Smalley <stephen.smalley.work@xxxxxxxxx>
Cc: Eric Paris <eparis@xxxxxxxxxxxxxx>
Cc: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
Cc: selinux@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 security/selinux/ss/sidtab.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/security/selinux/ss/sidtab.c b/security/selinux/ss/sidtab.c
index d8ead463b8df..732fd8e22a12 100644
--- a/security/selinux/ss/sidtab.c
+++ b/security/selinux/ss/sidtab.c
@@ -25,7 +25,7 @@ struct sidtab_str_cache {
 	struct list_head lru_member;
 	struct sidtab_entry *parent;
 	u32 len;
-	char str[];
+	char str[] __counted_by(len);
 };
 
 #define index_to_sid(index) ((index) + SECINITSID_NUM + 1)
-- 
2.34.1