linux-kernel - Re: [PATCH v3] scsi: target: Replace strlcpy with strscpy

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Message-ID: <202308311402.8F9854D6A@keescook>
Date:   Thu, 31 Aug 2023 14:02:36 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Azeem Shaikh <azeemshaikh38@...il.com>
Cc:     "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-hardening@...r.kernel.org, linux-scsi@...r.kernel.org,
        target-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] scsi: target: Replace strlcpy with strscpy

On Thu, Aug 31, 2023 at 03:20:47PM -0400, Azeem Shaikh wrote:
> On Thu, Aug 31, 2023 at 2:42 PM Kees Cook <keescook@...omium.org> wrote:
> >
> > On Thu, Aug 31, 2023 at 02:36:38PM +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 -errno
> > > 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>
> > > ---
> > > v3:
> > >  * Address readability comment.
> > >
> > > v2:
> > >  * Replace all instances of strlcpy in this file instead of just 1.
> > >  * https://lore.kernel.org/all/20230830210724.4156575-1-azeemshaikh38@gmail.com/
> > >
> > > v1:
> > >  * https://lore.kernel.org/all/20230830200717.4129442-1-azeemshaikh38@gmail.com/
> > >
> > >  drivers/target/target_core_configfs.c |   24 ++++++++++++------------
> > >  1 file changed, 12 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/drivers/target/target_core_configfs.c b/drivers/target/target_core_configfs.c
> > > index 936e5ff1b209..d5860c1c1f46 100644
> > > --- a/drivers/target/target_core_configfs.c
> > > +++ b/drivers/target/target_core_configfs.c
> > > @@ -1392,16 +1392,16 @@ static ssize_t target_wwn_vendor_id_store(struct config_item *item,
> > >       /* +2 to allow for a trailing (stripped) '\n' and null-terminator */
> > >       unsigned char buf[INQUIRY_VENDOR_LEN + 2];
> > >       char *stripped = NULL;
> > > -     size_t len;
> > > +     ssize_t len;
> > >       ssize_t ret;
> > >
> > > -     len = strlcpy(buf, page, sizeof(buf));
> > > -     if (len < sizeof(buf)) {
> > > +     len = strscpy(buf, page, sizeof(buf));
> > > +     if (len > 0) {
> > >               /* Strip any newline added from userspace. */
> > >               stripped = strstrip(buf);
> > >               len = strlen(stripped);
> > >       }
> > > -     if (len > INQUIRY_VENDOR_LEN) {
> > > +     if (len < 0 || len > INQUIRY_VENDOR_LEN) {
> >
> > Agh, sorry I missed this before: the first "if" needs to be "len >= 0"
> > otherwise this:
> >
> >         ret = target_check_inquiry_data(stripped);
> >
> > will be passing a NULL pointer...
> >
> 
> Hmm, the current implementation of strscpy never returns 0. If
> sizeof(buf) is 0, it'll return -E2BIG. Do you still prefer that I
> update this to check for len >= 0?

Oh right! Nevermind, then. Fine as-is. :)

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook