linux-hardening - Re: [PATCH v2] scsi: zfcp: Replace strlcpy() with strscpy()

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Date: Mon, 4 Dec 2023 18:17:31 +0100
From: Benjamin Block <bblock@...ux.ibm.com>
To: Kees Cook <keescook@...omium.org>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>
Cc: Steffen Maier <maier@...ux.ibm.com>, Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Azeem Shaikh <azeemshaikh38@...il.com>, linux-s390@...r.kernel.org,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] scsi: zfcp: Replace strlcpy() with strscpy()

Hello Kees, Martin, James,

On Thu, Nov 30, 2023 at 12:41:00PM -0800, Kees Cook wrote:
> strlcpy() reads the entire source buffer first. This read may exceed
> the destination size limit. This is both inefficient and can lead
> to linear read overflows if a source string is not NUL-terminated[1].
> Additionally, it returns the size of the source string, not the
> resulting size of the destination string. In an effort to remove strlcpy()
> completely[2], replace strlcpy() here with strscpy().
> 
> Overflow should be impossible here, but actually check for buffer sizes
> being identical with BUILD_BUG_ON(), and include a run-time check as
> well.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy [1]
> Link: https://github.com/KSPP/linux/issues/89 [2]

> ---
>  drivers/s390/scsi/zfcp_fc.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/s390/scsi/zfcp_fc.c b/drivers/s390/scsi/zfcp_fc.c
> index 4f0d0e55f0d4..d6516ab00437 100644
> --- a/drivers/s390/scsi/zfcp_fc.c
> +++ b/drivers/s390/scsi/zfcp_fc.c
> @@ -900,8 +900,19 @@ static void zfcp_fc_rspn(struct zfcp_adapter *adapter,
>  	zfcp_fc_ct_ns_init(&rspn_req->ct_hdr, FC_NS_RSPN_ID,
>  			   FC_SYMBOLIC_NAME_SIZE);
>  	hton24(rspn_req->rspn.fr_fid.fp_fid, fc_host_port_id(shost));
> -	len = strlcpy(rspn_req->rspn.fr_name, fc_host_symbolic_name(shost),
> -		      FC_SYMBOLIC_NAME_SIZE);
> +
> +	BUILD_BUG_ON(sizeof(rspn_req->name) !=
> +			sizeof(fc_host_symbolic_name(shost)));
> +	BUILD_BUG_ON(sizeof(rspn_req->name) !=
> +			type_max(typeof(rspn_req->rspn.fr_name_len)) + 1);
> +	len = strscpy(rspn_req->name, fc_host_symbolic_name(shost),
> +		      sizeof(rspn_req->name));
> +	/*
> +	 * It should be impossible for this to truncate (see BUILD_BUG_ON()
> +	 * above), but be robust anyway.
> +	 */
> +	if (WARN_ON(len < 0))
> +		len = sizeof(rspn_req->name) - 1;

Looks good to me.


Acked-by: Benjamin Block <bblock@...ux.ibm.com>


>  	rspn_req->rspn.fr_name_len = len;

Martin, James, can you please pick this up for the v6.8 queue?


-- 
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