linux-kernel - Re: [PATCH 10/11] staging: greybus: change strncpy() to strscpy()

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Date: Tue, 9 Apr 2024 10:09:21 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Arnd Bergmann <arnd@...nel.org>, Alex Elder <elder@...nel.org>
Cc: linux-kernel@...r.kernel.org, Viresh Kumar <vireshk@...nel.org>,
	Johan Hovold <johan@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	Christophe JAILLET <christophe.jaillet@...adoo.fr>,
	greybus-dev@...ts.linaro.org, linux-staging@...ts.linux.dev
Subject: Re: [PATCH 10/11] staging: greybus: change strncpy() to strscpy()

On Mon, Apr 08, 2024 at 08:26:00PM +0200, Arnd Bergmann wrote:
> On Thu, Mar 28, 2024, at 16:00, Dan Carpenter wrote:
> > On Thu, Mar 28, 2024 at 03:04:54PM +0100, Arnd Bergmann wrote:
> >> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> >> ---
> >> This is from randconfig testing with random gcc versions, a .config to
> >> reproduce is at https://pastebin.com/r13yezkU
> >> ---
> >>  drivers/staging/greybus/fw-management.c | 4 ++--
> >>  1 file changed, 2 insertions(+), 2 deletions(-)
> >> 
> >> diff --git a/drivers/staging/greybus/fw-management.c b/drivers/staging/greybus/fw-management.c
> >> index 3054f084d777..35bfdd5f32d2 100644
> >> --- a/drivers/staging/greybus/fw-management.c
> >> +++ b/drivers/staging/greybus/fw-management.c
> >> @@ -303,13 +303,13 @@ static int fw_mgmt_backend_fw_update_operation(struct fw_mgmt *fw_mgmt,
> >>  	struct gb_fw_mgmt_backend_fw_update_request request;
> >>  	int ret;
> >>  
> >> -	strncpy(request.firmware_tag, tag, GB_FIRMWARE_TAG_MAX_SIZE);
> >> +	ret = strscpy(request.firmware_tag, tag, GB_FIRMWARE_TAG_MAX_SIZE);
> >
> > This needs to be strscpy_pad() or it risks an information leak.
> 
> Right, I think I misread the code thinking that the strncpy()
> destination was user provided, but I see now that this copy is
> from user-provided data into the stack, so the padding is indeed
> stale stack data.
> 
> I could not find out whether this gets copied back to userspace,
> but adding the padding is safer indeed.
> 

Grey bus is a bus, I'm not sure what's on the other end of the bus but
I think we've generally said that the data needs to be zeroed...
Although if that is true, why didn't I make this a Smatch warning?

regards,
dan carpenter