less size_t please (was Re: [PATCH net] xfrm: fix integer overflow in xfrm_replay_state_esn_len())
From: Alexey Dobriyan
Date: Thu Jan 30 2025 - 08:45:04 EST
> -static inline unsigned int xfrm_replay_state_esn_len(struct xfrm_replay_state_esn *replay_esn)
> +static inline size_t xfrm_replay_state_esn_len(struct xfrm_replay_state_esn *replay_esn)
> {
> - return sizeof(*replay_esn) + replay_esn->bmp_len * sizeof(__u32);
> + return size_add(sizeof(*replay_esn), size_mul(replay_esn->bmp_len, sizeof(__u32)));
Please don't do this.
You can (and should!) make calculations and check for overflow at the
same time. It's very efficient.
> 1) Use size_add() and size_mul(). This change is necessary for 32bit systems.
This bloats code on 32-bit.
int len;
if (__builtin_mul_overflow(replay_esn->bmp_len, 4, &len)) {
return true;
}
if (__builtin_add_overflow(len, sizeof(*replay_esn), &len)) {
return true;
}
*plen = len;
return false;