linux-kernel - Re: [PATCH] ACPI / CPPC: Fix negative array index read in cppc_set

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Date:   Sat, 16 Dec 2017 02:47:30 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     "Gustavo A. R. Silva" <garsilva@...eddedor.com>
Cc:     Len Brown <lenb@...nel.org>,
        George Cherian <george.cherian@...ium.com>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ACPI / CPPC: Fix negative array index read in cppc_set_perf

On Wednesday, December 13, 2017 11:45:41 PM CET Gustavo A. R. Silva wrote:
> If pcc_ss_id is less than 0, there is a negative array index read
> before verifying pcc_ss_id is not a negative value.
> 
> Fix this by removing the code that triggers this issue.
> 
> Notice that this code is already properly placed after the check
> on pcc_ss_id at line 1182: pcc_ss_data = pcc_data[pcc_ss_id];
> 
> Addresses-Coverity-ID: 1426090 ("Negative array index read")
> Fixes: 1ecbd7170d65 ("ACPI / CPPC: Fix KASAN global out of bounds warning")
> Signed-off-by: Gustavo A. R. Silva <garsilva@...eddedor.com>
> ---
>  drivers/acpi/cppc_acpi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 30e84cc..06ea474 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -1171,7 +1171,7 @@ int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
>  	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
>  	struct cpc_register_resource *desired_reg;
>  	int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpu);
> -	struct cppc_pcc_data *pcc_ss_data = pcc_data[pcc_ss_id];
> +	struct cppc_pcc_data *pcc_ss_data;
>  	int ret = 0;
>  
>  	if (!cpc_desc || pcc_ss_id < 0) {
> 

I applied a patch from Coling Ian King that did the same thing and was
posted eaelier.

Thanks,
Rafael