Re: [PATCH v2] The value may overflow

[Mathieu Desnoyers]

On 9/4/23 05:42, Denis Arefev wrote:
> The value of an arithmetic expression 1 << (cpu - sdp->mynode->grplo)
> is subject to overflow due to a failure to cast operands to a larger
> data type before performing arithmetic

The patch title should identify more precisely its context, e.g.:

"srcu: Fix srcu_struct node grpmask overflow on 64-bit systems"

Also, as I stated in my reply to the previous version, the patch commit
message should describe the impact of the bug it fixes.

Thanks,

Mathieu


> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> Signed-off-by: Denis Arefev <arefev@xxxxxxxxx>
> ---
> v2: Added fixes to the srcu_schedule_cbs_snp function as suggested by
> Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
>   kernel/rcu/srcutree.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index 20d7a238d675..6c18e6005ae1 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -223,7 +223,7 @@ static bool init_srcu_struct_nodes(struct srcu_struct *ssp, gfp_t gfp_flags)
>   				snp->grplo = cpu;
>   			snp->grphi = cpu;
>   		}
> -		sdp->grpmask = 1 << (cpu - sdp->mynode->grplo);
> +		sdp->grpmask = 1UL << (cpu - sdp->mynode->grplo);
>   	}
>   	smp_store_release(&ssp->srcu_sup->srcu_size_state, SRCU_SIZE_WAIT_BARRIER);
>   	return true;
> @@ -833,7 +833,7 @@ static void srcu_schedule_cbs_snp(struct srcu_struct *ssp, struct srcu_node *snp
>   	int cpu;
>   
>   	for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) {
> -		if (!(mask & (1 << (cpu - snp->grplo))))
> +		if (!(mask & (1UL << (cpu - snp->grplo))))
>   			continue;
>   		srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, cpu), delay);
>   	}

--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com