From: Justin Stitt <justinstitt@google.com>
To: Kees Cook <kees@kernel.org>
Cc: James Smart <james.smart@broadcom.com>,
Dick Kennedy <dick.kennedy@broadcom.com>,
"James E.J. Bottomley" <jejb@linux.ibm.com>,
"Martin K. Petersen" <martin.petersen@oracle.com>,
linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-hardening@vger.kernel.org
Subject: Re: [PATCH] scsi: lpfc: replace deprecated strncpy with strscpy
Date: Fri, 23 Feb 2024 12:02:22 -0800 [thread overview]
Message-ID: <CAFhGd8rTBqqQvr9vhpbfcSv6cpj5JSPVPSftqOPyWkZEWBP1AQ@mail.gmail.com> (raw)
In-Reply-To: <BE9C61AA-633F-4CD1-BE5E-B01DC947626E@kernel.org>
Hi,
On Wed, Feb 21, 2024 at 6:38 PM Kees Cook <kees@kernel.org> wrote:
>
>
>
> On February 21, 2024 4:41:52 PM PST, Justin Stitt <justinstitt@google.com> wrote:
> >strncpy() is deprecated for use on NUL-terminated destination strings
> >[1] and as such we should prefer more robust and less ambiguous string
> >interfaces.
> >
> >We expect ae->value_string to be NUL-terminated because there's a
> >comment that says as much; these attr strings are also used with other
> >string APIs, further cementing the fact.
> >
> >Now, the question of whether or not to NUL-pad the destination buffer:
> >lpfc_fdmi_rprt_defer() initializes vports (all zero-initialized), then
> >we call lpfc_fdmi_cmd() with each vport and a mask. Then, inside of
> >lpfc_fdmi_cmd() we check each bit in the mask to invoke the proper
> >callback. Importantly, the zero-initialized vport is passed in as the
> >"attr" parameter. Seeing this:
> >| struct lpfc_fdmi_attr_string *ae = attr;
> >... we can tell that ae->value_string is entirely zero-initialized. Due
> >to this, NUL-padding is _not_ required as it would be redundant.
> >
> >Conveniently, strscpy also returns the number of bytes copied into the
> >destination buffer, eliminating the need for strnlen!
> >
> >Considering the above, a suitable replacement is `strscpy` [2].
> >
> >Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> >Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
> >Link: https://github.com/KSPP/linux/issues/90
> >Cc: linux-hardening@vger.kernel.org
> >Signed-off-by: Justin Stitt <justinstitt@google.com>
> >---
> > drivers/scsi/lpfc/lpfc_ct.c | 5 ++---
> > 1 file changed, 2 insertions(+), 3 deletions(-)
> >
> >diff --git a/drivers/scsi/lpfc/lpfc_ct.c b/drivers/scsi/lpfc/lpfc_ct.c
> >index baae1f8279e0..42594ec87290 100644
> >--- a/drivers/scsi/lpfc/lpfc_ct.c
> >+++ b/drivers/scsi/lpfc/lpfc_ct.c
> >@@ -2569,9 +2569,8 @@ lpfc_fdmi_set_attr_string(void *attr, uint16_t attrtype, char *attrstring)
> > * 64 bytes or less.
> > */
> >
> >- strncpy(ae->value_string, attrstring, sizeof(ae->value_string));
> >- len = strnlen(ae->value_string, sizeof(ae->value_string));
> >- /* round string length to a 32bit boundary. Ensure there's a NULL */
> >+ len = strscpy(ae->value_string, attrstring, sizeof(ae->value_string));
>
> This could be < 0 on error, and at least lpfc_fdmi_hba_attr_os_ver() may present more than 64 bytes...
Am I putting too much faith in this comment?
static inline int lpfc_fdmi_set_attr_string(void *attr, uint16_t
attrtype, char *attrstring)
...
/*
* We are trusting the caller that if a fdmi string field
* is capped at 64 bytes, the caller passes in a string of
* 64 bytes or less.
*/
...
I see lpfc_fdmi_hba_attr_os_ver() calls lpfc_fdmi_set_attr_string()
with an attrstring sized at 256 bytes:
char buf[256] = { 0 };
Can we really return -E2BIG from strscpy() if the dest buffer is the
same size as the source buffer?
I'm happy to just make the standard strncpy -> strscpy replacement and
drop the len assignment. Let me know what you think, Kees.
>
> -Kees
>
>
> >+ /* round string length to a 32bit boundary */
> > len += (len & 3) ? (4 - (len & 3)) : 4;
> > /* size is Type/Len (4 bytes) plus string length */
> > size = FOURBYTES + len;
> >
> >---
> >base-commit: 39133352cbed6626956d38ed72012f49b0421e7b
> >change-id: 20240222-strncpy-drivers-scsi-lpfc-lpfc_ct-c-f54b67eeeb68
> >
> >Best regards,
> >--
> >Justin Stitt <justinstitt@google.com>
> >
> >
>
> --
> Kees Cook
Thanks
Justin
next prev parent reply other threads:[~2024-02-23 20:02 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-22 0:41 [PATCH] scsi: lpfc: replace deprecated strncpy with strscpy Justin Stitt
2024-02-22 2:37 ` Kees Cook
2024-02-23 20:02 ` Justin Stitt [this message]
2024-02-23 23:44 ` Kees Cook
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAFhGd8rTBqqQvr9vhpbfcSv6cpj5JSPVPSftqOPyWkZEWBP1AQ@mail.gmail.com \
--to=justinstitt@google.com \
--cc=dick.kennedy@broadcom.com \
--cc=james.smart@broadcom.com \
--cc=jejb@linux.ibm.com \
--cc=kees@kernel.org \
--cc=linux-hardening@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-scsi@vger.kernel.org \
--cc=martin.petersen@oracle.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).