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Date: Tue, 24 Oct 2023 17:42:10 -0700
From: Kees Cook <keescook@...omium.org>
To: Justin Stitt <justinstitt@...gle.com>
Cc: James Smart <james.smart@...adcom.com>,
	Ram Vegesna <ram.vegesna@...adcom.com>,
	"James E.J. Bottomley" <jejb@...ux.ibm.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	linux-scsi@...r.kernel.org, target-devel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] scsi: elx: libefc: replace deprecated strncpy with
 strscpy

On Mon, Oct 23, 2023 at 09:58:32PM +0000, Justin Stitt wrote:
> strncpy() is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces.
> 
> A suitable replacement is `strscpy` [2] due to the fact that it
> guarantees NUL-termination on the destination buffer without
> unnecessarily NUL-padding.
> 
> There seems to not be any uses of `current_state_name` other than in
> these assignments. Judging from context surrounding these assignments,
> especially considering the string literal "invalid" being assigned, we
> want both current_state_name and prev_state_name to be NUL-terminated
> strings.

I'm nervous that "node" may be either passed over the link or in
IO memory, so the behavior change of not %NUL-padding these may trip
something at run-time. Unless someone says otherwise, let's stay on the
safe side and use strscpy_pad() for "invalid" and handler, and memcpy()
for the swap.

Looking at "handler", it's always less than 64, so we don't need to
worry about early truncation -- it's always __func__, and none of them
are very long:

$ git grep efc_node_evt_set | grep -v __func__
drivers/scsi/elx/libefc/efc_node.h:efc_node_evt_set(struct efc_sm_ctx *ctx, enum efc_sm_event evt,

$ git grep efc_node_evt_set | grep __func__ | cut -d: -f1 | sort -u
drivers/scsi/elx/libefc/efc_device.c
drivers/scsi/elx/libefc/efc_fabric.c
drivers/scsi/elx/libefc/efc_node.c

$ grep -E '^_?_?efc' drivers/scsi/elx/libefc/efc_{fabric,device,node}.c \
  | cut -d'(' -f1 | cut -d: -f2 | wc -L
37

-Kees

> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> ---
> Note: build-tested only.
> 
> Found with: $ rg "strncpy\("
> ---
>  drivers/scsi/elx/libefc/efc_node.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/elx/libefc/efc_node.h b/drivers/scsi/elx/libefc/efc_node.h
> index e9c600ac45d5..3a16703d0f97 100644
> --- a/drivers/scsi/elx/libefc/efc_node.h
> +++ b/drivers/scsi/elx/libefc/efc_node.h
> @@ -26,12 +26,12 @@ efc_node_evt_set(struct efc_sm_ctx *ctx, enum efc_sm_event evt,
>  	struct efc_node *node = ctx->app;
>  
>  	if (evt == EFC_EVT_ENTER) {
> -		strncpy(node->current_state_name, handler,
> +		strscpy(node->current_state_name, handler,
>  			sizeof(node->current_state_name));
>  	} else if (evt == EFC_EVT_EXIT) {
> -		strncpy(node->prev_state_name, node->current_state_name,
> +		strscpy(node->prev_state_name, node->current_state_name,
>  			sizeof(node->prev_state_name));
> -		strncpy(node->current_state_name, "invalid",
> +		strscpy(node->current_state_name, "invalid",
>  			sizeof(node->current_state_name));
>  	}
>  	node->prev_evt = node->current_evt;
> 
> ---
> base-commit: 9c5d00cb7b6bbc5a7965d9ab7d223b5402d1f02c
> change-id: 20231023-strncpy-drivers-scsi-elx-libefc-efc_node-h-cbbf753197b7
> 
> Best regards,
> --
> Justin Stitt <justinstitt@...gle.com>
> 
> 

-- 
Kees Cook

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