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

From: Dan Carpenter <dan.carpenter@linaro.org>
To: Arnd Bergmann <arnd@kernel.org>, Alex Elder <elder@kernel.org>
Cc: linux-kernel@vger.kernel.org, Viresh Kumar <vireshk@kernel.org>,
	Johan Hovold <johan@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
	greybus-dev@lists.linaro.org, linux-staging@lists.linux.dev
Subject: Re: [PATCH 10/11] staging: greybus: change strncpy() to strscpy()
Date: Tue, 9 Apr 2024 10:09:21 +0300	[thread overview]
Message-ID: <3bdbb7aa-d9b4-40ec-836b-ae5978cda9e0@moroto.mountain> (raw)
In-Reply-To: <1622d9ff-feed-4a12-9d8d-3f00088c9edf@app.fastmail.com>

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@arndb.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