Re: [PATCH iwl-next] ice: prevent integer overflow

[Simon Horman <horms@kernel.org>]

On Fri, Mar 20, 2026 at 06:05:44AM +0100, Aleksandr Loktionov wrote:
> From: Lukasz Czapnik <lukasz.czapnik@intel.com>
> 
> In ice_sched_bw_to_rl_profile(), the loop over 64 bits computes the
> scheduler timestamp rate as:
> 
>   ts_rate = div64_long((s64)hw->psm_clk_freq,
>                        pow_result * ICE_RL_PROF_TS_MULTIPLIER);
> 
> where pow_result = BIT_ULL(i). For large values of i, the product
> pow_result * ICE_RL_PROF_TS_MULTIPLIER overflows u64 before being used
> as the divisor, producing incorrect ts_rate values and potentially
> undefined behaviour.
> 
> Fix this by pre-computing ts_freq = hw->psm_clk_freq /
> ICE_RL_PROF_TS_MULTIPLIER once before the loop and then dividing only
> by pow_result inside the loop. The division order avoids the overflow
> while preserving the same mathematical result. Declare ts_freq as s64
> to match the type domain of the surrounding arithmetic and avoid a
> redundant cast at the use site.
> 
> While at it, scope the loop variable i to the for statement itself.
> 
> Fixes: 1ddef455f4a8 ("ice: Add NDO callback to set the maximum per-queue bitrate")
> Signed-off-by: Lukasz Czapnik <lukasz.czapnik@intel.com>
> Signed-off-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>

Reviewed-by: Simon Horman <horms@kernel.org>