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

Dan Carpenter
2024-04-09T07:09:27Z

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