linux-kernel - Re: [PATCH v2] powerpc/rtas_flash: fix a potential buffer overflow

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Message-ID: <20210714185224.Horde.SuBZAzTXvfB6J6HsqQkOog6@messagerie.c-s.fr>
Date:   Wed, 14 Jul 2021 18:52:24 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Yi Zhuang <zhuangyi1@...wei.com>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        hegdevasant@...ux.vnet.ibm.com, paulus@...ba.org,
        benh@...nel.crashing.org
Subject: Re: [PATCH v2] powerpc/rtas_flash: fix a potential buffer overflow

Yi Zhuang <zhuangyi1@...wei.com> a écrit :

> Since snprintf() returns the possible output size instead of the
> actual output size, the available flash_msg length returned by
> get_validate_flash_msg may exceed the given buffer limit when
> simple_read_from_buffer calls copy_to_user
>
> Reported-by: kernel test robot <lkp@...el.com>
> Fixes: a94a14720eaf5 powerpc/rtas_flash: Fix validate_flash buffer  
> overflow issue
> Signed-off-by: Yi Zhuang <zhuangyi1@...wei.com>
> ---
>  arch/powerpc/kernel/rtas_flash.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kernel/rtas_flash.c  
> b/arch/powerpc/kernel/rtas_flash.c
> index a99179d83538..062f0724c2ff 100644
> --- a/arch/powerpc/kernel/rtas_flash.c
> +++ b/arch/powerpc/kernel/rtas_flash.c
> @@ -470,9 +470,14 @@ static int get_validate_flash_msg(struct  
> rtas_validate_flash_t *args_buf,
>  	if (args_buf->status >= VALIDATE_TMP_UPDATE) {
>  		n = sprintf(msg, "%d\n", args_buf->update_results);
>  		if ((args_buf->update_results >= VALIDATE_CUR_UNKNOWN) ||
> -		    (args_buf->update_results == VALIDATE_TMP_UPDATE))
> +		    (args_buf->update_results == VALIDATE_TMP_UPDATE)) {
>  			n += snprintf(msg + n, msglen - n, "%s\n",
>  					args_buf->buf);
> +			if (n >= msglen) {

n cannot be greater than msglen


> +				n = msglen;
> +				printk(KERN_ERR "FLASH: msg too long.\n");
> +			}
> +		}
>  	} else {
>  		n = sprintf(msg, "%d\n", args_buf->status);
>  	}
> --
> 2.26.0.106.g9fadedd