linux-kernel - Re: [PATCH] ucounts: fix counter leak in inc_rlimit_get

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Message-ID: <ZyNS9J7TOQ84AkYz@example.org>
Date: Thu, 31 Oct 2024 10:50:44 +0100
From: Alexey Gladkov <legion@...nel.org>
To: Andrei Vagin <avagin@...gle.com>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>,
	Kees Cook <kees@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] ucounts: fix counter leak in inc_rlimit_get_ucounts()

On Thu, Oct 31, 2024 at 04:56:01AM +0000, Andrei Vagin wrote:
> The inc_rlimit_get_ucounts() increments the specified rlimit counter and
> then checks its limit. If the value exceeds the limit, the function
> returns an error without decrementing the counter.
> 
> Fixes: 15bc01effefe ("ucounts: Fix signal ucount refcounting")
> Tested-by: Roman Gushchin <roman.gushchin@...ux.dev>
> Co-debugged-by: Roman Gushchin <roman.gushchin@...ux.dev>
> Cc: Kees Cook <kees@...nel.org>
> Cc: Andrei Vagin <avagin@...gle.com>
> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
> Cc: Alexey Gladkov <legion@...nel.org>
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Andrei Vagin <avagin@...gle.com>
> ---
>  kernel/ucount.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/ucount.c b/kernel/ucount.c
> index 8c07714ff27d..16c0ea1cb432 100644
> --- a/kernel/ucount.c
> +++ b/kernel/ucount.c
> @@ -328,13 +328,12 @@ long inc_rlimit_get_ucounts(struct ucounts *ucounts, enum rlimit_type type)
>  		if (new != 1)
>  			continue;
>  		if (!get_ucounts(iter))
> -			goto dec_unwind;
> +			goto unwind;
>  	}
>  	return ret;
> -dec_unwind:
> +unwind:
>  	dec = atomic_long_sub_return(1, &iter->rlimit[type]);
>  	WARN_ON_ONCE(dec < 0);
> -unwind:
>  	do_dec_rlimit_put_ucounts(ucounts, iter, type);
>  	return 0;
>  }

Agree. The do_dec_rlimit_put_ucounts() decreases rlimit up to iter but
does not include it.

Except for a small NAK because the patch changes goto for get_ucounts()
and not for rlimit overflow check.

Acked-by: Alexey Gladkov <legion@...nel.org>

-- 
Rgrds, legion