linux-kernel - Re: [PATCH] mm/mlock: fix potential imbalanced rlimit ucounts adjustment

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Date:   Sun, 13 Mar 2022 19:40:08 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Miaohe Lin <linmiaohe@...wei.com>
cc:     akpm@...ux-foundation.org, Herbert.van.den.Bergh@...cle.com,
        chris.mason@...cle.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/mlock: fix potential imbalanced rlimit ucounts
 adjustment

On Thu, 10 Mar 2022, Miaohe Lin wrote:

> user_shm_lock forgets to set allowed to 0 when get_ucounts fails. So
> the later user_shm_unlock might do the extra dec_rlimit_ucounts. Fix
> this by resetting allowed to 0.
> 
> Fixes: 5ed44a401ddf ("do not limit locked memory when RLIMIT_MEMLOCK is RLIM_INFINITY")
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>

NAK.  user_shm_lock() remembers to declare "int allowed = 0" on entry.

> ---
>  mm/mlock.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 29372c0eebe5..efd2dd2943de 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -733,6 +733,7 @@ int user_shm_lock(size_t size, struct ucounts *ucounts)
>  	}
>  	if (!get_ucounts(ucounts)) {
>  		dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked);
> +		allowed = 0;
>  		goto out;
>  	}
>  	allowed = 1;
> -- 
> 2.23.0
> 
> 
>