Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Anders Larsen <al@alarsen.net>
To:     Tong Zhang <ztong0001@gmail.com>
Cc:     linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1] qnx4_match: do not over run the buffer
Date:   Sat, 21 Nov 2020 22:40:17 +0100
Message-ID: <2474566.rpppqFFLNx@alarsen.net>
In-Reply-To: <20201120212120.2502522-1-ztong0001@gmail.com>
References: <20201120212120.2502522-1-ztong0001@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 7Bit
Content-Type: text/plain; charset="us-ascii"
Precedence: bulk

On Friday, 2020-11-20 22:21 Tong Zhang wrote:
> the di_fname may not terminated by '\0', use strnlen to prevent buffer
> overrun
> 
> ---
>  fs/qnx4/namei.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
> index 8d72221735d7..c0e79094f578 100644
> --- a/fs/qnx4/namei.c
> +++ b/fs/qnx4/namei.c
> @@ -40,7 +40,7 @@ static int qnx4_match(int len, const char *name,
>  	} else {
>  		namelen = QNX4_SHORT_NAME_MAX;
>  	}
> -	thislen = strlen( de->di_fname );
> +	thislen = strnlen( de->di_fname, QNX4_SHORT_NAME_MAX );

that should be
+	thislen = strnlen( de->di_fname, namelen );
otherwise the length of a filename would always be limited to QNX4_SHORT_NAME_MAX (16) characters.

>  	if ( thislen > namelen )
>  		thislen = namelen;

These two lines can be dropped now, as the result of strnlen() cannot exceed namelen anyway.

Cheers
Anders