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

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Date: Mon, 20 Nov 2023 13:40:49 +0100
From: Benjamin Block <bblock@...ux.ibm.com>
To: Kees Cook <keescook@...omium.org>, Steffen Maier <maier@...ux.ibm.com>
Cc: 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-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
        Mailing List linux-scsi <linux-scsi@...r.kernel.org>
Subject: Re: [PATCH] scsi: zfcp: Replace strlcpy() with strscpy()

Hey Kees,

thanks for the patch.

can you please send this patch to linux-scsi and CC the SCSI Maintainers
(Martin and James) instead (having linux-s390 on CC is fine)? zFCP doesn't go
via s390, being a SCSI driver.

On Thu, Nov 16, 2023 at 11:14:35AM -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().
> 
> Be explicitly robust in the face of truncation, which should be an
> impossible state.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy [1]
> Link: https://github.com/KSPP/linux/issues/89 [2]
> Cc: Steffen Maier <maier@...ux.ibm.com>
> Cc: Benjamin Block <bblock@...ux.ibm.com>
> Cc: Heiko Carstens <hca@...ux.ibm.com>
> Cc: Vasily Gorbik <gor@...ux.ibm.com>
> Cc: Alexander Gordeev <agordeev@...ux.ibm.com>
> Cc: Christian Borntraeger <borntraeger@...ux.ibm.com>
> Cc: Sven Schnelle <svens@...ux.ibm.com>
> Cc: Azeem Shaikh <azeemshaikh38@...il.com>
> Cc: linux-s390@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  drivers/s390/scsi/zfcp_fc.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/s390/scsi/zfcp_fc.c b/drivers/s390/scsi/zfcp_fc.c
> index 4f0d0e55f0d4..1a29f10767fc 100644
> --- a/drivers/s390/scsi/zfcp_fc.c
> +++ b/drivers/s390/scsi/zfcp_fc.c
> @@ -900,8 +900,15 @@ 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);
> +	len = strscpy(rspn_req->name, fc_host_symbolic_name(shost),
> +		      sizeof(rspn_req->name));

This is corrct.

> +	/*
> +	 * It should be impossible for this to truncate, as
> +	 * sizeof(rspn_req->name) is equal to max size of
> +	 * fc_host_symbolic_name(shost), but check anyway.
> +	 */
> +	if (len < 0)
> +		len = sizeof(rspn_req->name) - 1;

I'd rather have a compile-time check, whether the array sizes of
`rspn_req->name` and `fc_host_symbolic_name(shost)` run out of sync, or
against our expectations.

Something like:

	len = strscpy(rspn_req->name, fc_host_symbolic_name(shost),
		      sizeof(rspn_req->name));
	BUILD_BUG_ON(sizeof(rspn_req->name) !=
			     sizeof(fc_host_symbolic_name(shost)) ||
		     sizeof(rspn_req->name) !=
			     1 << sizeof(rspn_req->rspn.fr_name_len) * 8);
	rspn_req->rspn.fr_name_len = len;

Then the last assignment should also be correct; and if something changes -
unexpectedly, because this follows a FC standard - we need to adapt the code
anyway I'd think.

Or am I missing something?

>	rspn_req->rspn.fr_name_len = len;
>  
>	sg_init_one(&fc_req->sg_req, rspn_req, sizeof(*rspn_req));
> -- 
> 2.34.1
> 

-- 
Best Regards, Benjamin Block        /        Linux on IBM Z Kernel Development
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