Re: [PATCH] usb: gadget: function: printer: Replace strlcpy with strscpy

[Azeem Shaikh]

On Tue, Jun 13, 2023 at 3:30 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> On Tue, Jun 13, 2023 at 12:43:41AM +0000, Azeem Shaikh 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].
> > In an effort to remove strlcpy() completely [2], replace
> > strlcpy() here with strscpy().
> >
> > Direct replacement is safe here since return value of -E2BIG
> > is used to check for truncation instead of sizeof(dest).
>
> Perhaps say "PAGE_SIZE" here instead of sizeof(dest)?
>

Ack.

> >
> > [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
> > [2] https://github.com/KSPP/linux/issues/89
> >
> > Signed-off-by: Azeem Shaikh <azeemshaikh38@xxxxxxxxx>
> > ---
> >  drivers/usb/gadget/function/f_printer.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/usb/gadget/function/f_printer.c b/drivers/usb/gadget/function/f_printer.c
> > index 28db3e336e7d..10dc7c55c25f 100644
> > --- a/drivers/usb/gadget/function/f_printer.c
> > +++ b/drivers/usb/gadget/function/f_printer.c
> > @@ -1211,8 +1211,8 @@ static ssize_t f_printer_opts_pnp_string_show(struct config_item *item,
> >       if (!opts->pnp_string)
> >               goto unlock;
> >
> > -     result = strlcpy(page, opts->pnp_string, PAGE_SIZE);
> > -     if (result >= PAGE_SIZE) {
> > +     result = strscpy(page, opts->pnp_string, PAGE_SIZE);
> > +     if (result == -E2BIG) {
>
> I think "< 1" might be a better test here.
>

Curious, why "< 1" instead of "< 0"?

> >               result = PAGE_SIZE;
> >       } else if (page[result - 1] != '\n' && result + 1 < PAGE_SIZE) {
> >               page[result++] = '\n';
> > --
> > 2.41.0.162.gfafddb0af9-goog
> >
> >
>
> -Kees
>
> --
> Kees Cook