linux-hardening - Re: [PATCH] usbip: usbip_host: Replace strlcpy with strscpy

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Date:   Wed, 14 Jun 2023 10:10:59 -0400
From:   Azeem Shaikh <azeemshaikh38@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Valentina Manea <valentina.manea.m@...il.com>,
        Shuah Khan <shuah@...nel.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        linux-hardening@...r.kernel.org, Hongren Zheng <i@...ithal.me>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usbip: usbip_host: Replace strlcpy with strscpy

On Tue, Jun 13, 2023 at 3:31 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Tue, Jun 13, 2023 at 12:44:02AM +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).
> >
> > [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@...il.com>
> > ---
> >  drivers/usb/usbip/stub_main.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/usb/usbip/stub_main.c b/drivers/usb/usbip/stub_main.c
> > index e8c3131a8543..a92a284f5abb 100644
> > --- a/drivers/usb/usbip/stub_main.c
> > +++ b/drivers/usb/usbip/stub_main.c
> > @@ -174,8 +174,8 @@ static ssize_t match_busid_store(struct device_driver *dev, const char *buf,
> >               return -EINVAL;
> >
> >       /* busid needs to include \0 termination */
> > -     len = strlcpy(busid, buf + 4, BUSID_SIZE);
> > -     if (sizeof(busid) <= len)
> > +     len = strscpy(busid, buf + 4, BUSID_SIZE);
> > +     if (len == -E2BIG)
> >               return -EINVAL;
>
> "len" is never used again, so maybe:
>
>         if (strscpy(...) < 0)
>                 return -EINVAL;
>
> -Kees
>

Thanks. Sent v2.

> >
> >       if (!strncmp(buf, "add ", 4)) {
> > --
> > 2.41.0.162.gfafddb0af9-goog
> >
> >
>
> --
> Kees Cook