linux-kernel - Re: [PATCH v2 5/5] ucounts: Handle wrapping in is_ucounts

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Message-ID: <a616b08c-dcec-4a00-ca55-a333063157e9@linuxfoundation.org>
Date:   Wed, 16 Feb 2022 10:28:35 -0700
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-kernel@...r.kernel.org
Cc:     Alexey Gladkov <legion@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Shuah Khan <shuah@...nel.org>,
        Christian Brauner <brauner@...nel.org>,
        Solar Designer <solar@...nwall.com>,
        Ran Xiaokai <ran.xiaokai@....com.cn>,
        containers@...ts.linux-foundation.org,
        Michal Koutný <mkoutny@...e.com>,
        linux-api@...r.kernel.org, stable@...r.kernel.org,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v2 5/5] ucounts: Handle wrapping in is_ucounts_overlimit

On 2/16/22 8:58 AM, Eric W. Biederman wrote:
> While examining is_ucounts_overlimit and reading the various messages
> I realized that is_ucounts_overlimit fails to deal with counts that
> may have wrapped.
> 
> Being wrapped should be a transitory state for counts and they should
> never be wrapped for long, but it can happen so handle it.
> 
> Cc: stable@...r.kernel.org
> Fixes: 21d1c5e386bc ("Reimplement RLIMIT_NPROC on top of ucounts")
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> ---
>   kernel/ucount.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/ucount.c b/kernel/ucount.c
> index 65b597431c86..06ea04d44685 100644
> --- a/kernel/ucount.c
> +++ b/kernel/ucount.c
> @@ -350,7 +350,8 @@ bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsign
>   	if (rlimit > LONG_MAX)
>   		max = LONG_MAX;
>   	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
> -		if (get_ucounts_value(iter, type) > max)
> +		long val = get_ucounts_value(iter, type);
> +		if (val < 0 || val > max)
>   			return true;
>   		max = READ_ONCE(iter->ns->ucount_max[type]);
>   	}
> 

This addresses the concerns about overflow.

Reviewed-by: Shuah Khan <skhan@...uxfoundation.org>

thanks,
-- Shuah