crypto: af_alg - Annotate struct af_alg_iv with __counted_by

Add the __counted_by() compiler attribute to the flexible array member
'iv' to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
CONFIG_FORTIFY_SOURCE.

Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Link: https://patch.msgid.link/20260105122402.2685-2-thorsten.blum@linux.dev
Signed-off-by: Kees Cook <kees@kernel.org>

Author: toblux

include/uapi/linux/if_alg.h

@@ -42,7 +42,7 @@ struct sockaddr_alg_new {
 
 struct af_alg_iv {
 	__u32	ivlen;
-	__u8	iv[];
+	__u8	iv[] __counted_by(ivlen);
 };
 
 /* Socket options */