linux-kernel - Re: [PATCH] memcg_write_event_control(): fix a user-triggerable oops

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Message-ID: <ZqNLEc54NVP40Kpn@tiehlicka>
Date: Fri, 26 Jul 2024 09:06:57 +0200
From: Michal Hocko <mhocko@...e.com>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memcg_write_event_control(): fix a user-triggerable oops

On Fri 26-07-24 06:43:57, Al Viro wrote:
> We are *not* guaranteed that anything past the terminating NUL
> is mapped (let alone initialized with anything sane).
>     

Fixes: 0dea116876ee ("cgroup: implement eventfd-based generic API for notifications")

> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
> diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c
> index 2aeea4d8bf8e..417c96f2da28 100644
> --- a/mm/memcontrol-v1.c
> +++ b/mm/memcontrol-v1.c
> @@ -1842,9 +1842,12 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
>  	buf = endp + 1;
>  
>  	cfd = simple_strtoul(buf, &endp, 10);
> -	if ((*endp != ' ') && (*endp != '\0'))
> +	if (*endp == '\0')
> +		buf = endp;
> +	else if (*endp == ' ')
> +		buf = endp + 1;
> +	else
>  		return -EINVAL;
> -	buf = endp + 1;
>  
>  	event = kzalloc(sizeof(*event), GFP_KERNEL);
>  	if (!event)

-- 
Michal Hocko
SUSE Labs