linux-kernel - Re: [PATCH v1] qnx4_match: do not over run the buffer

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Date:   Sat, 21 Nov 2020 22:40:17 +0100
From:   Anders Larsen <al@...rsen.net>
To:     Tong Zhang <ztong0001@...il.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] qnx4_match: do not over run the buffer

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