linux-kernel - Re: [PATCH v1] drivers/vhost/vhost: fix overflow checks in vhost

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Message-ID: <20221207100028-mutt-send-email-mst@kernel.org>
Date:   Wed, 7 Dec 2022 10:01:53 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Daniil Tatianin <d-tatianin@...dex-team.ru>
Cc:     Jason Wang <jasowang@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] drivers/vhost/vhost: fix overflow checks in
 vhost_overflow

On Wed, Dec 07, 2022 at 04:46:31PM +0300, Daniil Tatianin wrote:
> The if statement would erroneously check for > ULONG_MAX, which could
> never evaluate to true. Check for equality instead.
> 
> Found by Linux Verification Center (linuxtesting.org) with the SVACE
> static analysis tool.
> 
> Signed-off-by: Daniil Tatianin <d-tatianin@...dex-team.ru>

It can trigger on a 32 bit system. I'd also expect more analysis
of the code flow than "this can not trigger switch to a condition
that can" to accompany a patch.

> ---
>  drivers/vhost/vhost.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 40097826cff0..8df706e7bc6c 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -730,7 +730,7 @@ static bool log_access_ok(void __user *log_base, u64 addr, unsigned long sz)
>  /* Make sure 64 bit math will not overflow. */
>  static bool vhost_overflow(u64 uaddr, u64 size)
>  {
> -	if (uaddr > ULONG_MAX || size > ULONG_MAX)
> +	if (uaddr == ULONG_MAX || size == ULONG_MAX)
>  		return true;
>  
>  	if (!size)
> -- 
> 2.25.1