[v1] scsi: zfcp: Replace strlcpy() with strscpy()

[PATCH] scsi: zfcp: Replace strlcpy() with strscpy()

Posted by Kees Cook 2 years, 1 month ago

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].
Additionally, it returns the size of the source string, not the
resulting size of the destination string. In an effort to remove strlcpy()
completely[2], replace strlcpy() here with strscpy().

Be explicitly robust in the face of truncation, which should be an
impossible state.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy [1]
Link: https://github.com/KSPP/linux/issues/89 [2]
Cc: Steffen Maier <maier@linux.ibm.com>
Cc: Benjamin Block <bblock@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Azeem Shaikh <azeemshaikh38@gmail.com>
Cc: linux-s390@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/s390/scsi/zfcp_fc.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/scsi/zfcp_fc.c b/drivers/s390/scsi/zfcp_fc.c
index 4f0d0e55f0d4..1a29f10767fc 100644
--- a/drivers/s390/scsi/zfcp_fc.c
+++ b/drivers/s390/scsi/zfcp_fc.c
@@ -900,8 +900,15 @@ static void zfcp_fc_rspn(struct zfcp_adapter *adapter,
 	zfcp_fc_ct_ns_init(&rspn_req->ct_hdr, FC_NS_RSPN_ID,
 			   FC_SYMBOLIC_NAME_SIZE);
 	hton24(rspn_req->rspn.fr_fid.fp_fid, fc_host_port_id(shost));
-	len = strlcpy(rspn_req->rspn.fr_name, fc_host_symbolic_name(shost),
-		      FC_SYMBOLIC_NAME_SIZE);
+	len = strscpy(rspn_req->name, fc_host_symbolic_name(shost),
+		      sizeof(rspn_req->name));
+	/*
+	 * It should be impossible for this to truncate, as
+	 * sizeof(rspn_req->name) is equal to max size of
+	 * fc_host_symbolic_name(shost), but check anyway.
+	 */
+	if (len < 0)
+		len = sizeof(rspn_req->name) - 1;
 	rspn_req->rspn.fr_name_len = len;
 
 	sg_init_one(&fc_req->sg_req, rspn_req, sizeof(*rspn_req));
-- 
2.34.1

Re: [PATCH] scsi: zfcp: Replace strlcpy() with strscpy()

Posted by Benjamin Block 2 years, 1 month ago

Hey Kees,

thanks for the patch.

can you please send this patch to linux-scsi and CC the SCSI Maintainers
(Martin and James) instead (having linux-s390 on CC is fine)? zFCP doesn't go
via s390, being a SCSI driver.

On Thu, Nov 16, 2023 at 11:14:35AM -0800, Kees Cook 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].
> Additionally, it returns the size of the source string, not the
> resulting size of the destination string. In an effort to remove strlcpy()
> completely[2], replace strlcpy() here with strscpy().
> 
> Be explicitly robust in the face of truncation, which should be an
> impossible state.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy [1]
> Link: https://github.com/KSPP/linux/issues/89 [2]
> Cc: Steffen Maier <maier@linux.ibm.com>
> Cc: Benjamin Block <bblock@linux.ibm.com>
> Cc: Heiko Carstens <hca@linux.ibm.com>
> Cc: Vasily Gorbik <gor@linux.ibm.com>
> Cc: Alexander Gordeev <agordeev@linux.ibm.com>
> Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
> Cc: Sven Schnelle <svens@linux.ibm.com>
> Cc: Azeem Shaikh <azeemshaikh38@gmail.com>
> Cc: linux-s390@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  drivers/s390/scsi/zfcp_fc.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/s390/scsi/zfcp_fc.c b/drivers/s390/scsi/zfcp_fc.c
> index 4f0d0e55f0d4..1a29f10767fc 100644
> --- a/drivers/s390/scsi/zfcp_fc.c
> +++ b/drivers/s390/scsi/zfcp_fc.c
> @@ -900,8 +900,15 @@ static void zfcp_fc_rspn(struct zfcp_adapter *adapter,
>	zfcp_fc_ct_ns_init(&rspn_req->ct_hdr, FC_NS_RSPN_ID,
>			   FC_SYMBOLIC_NAME_SIZE);
>	hton24(rspn_req->rspn.fr_fid.fp_fid, fc_host_port_id(shost));
> -	len = strlcpy(rspn_req->rspn.fr_name, fc_host_symbolic_name(shost),
> -		      FC_SYMBOLIC_NAME_SIZE);
> +	len = strscpy(rspn_req->name, fc_host_symbolic_name(shost),
> +		      sizeof(rspn_req->name));

This is corrct.

> +	/*
> +	 * It should be impossible for this to truncate, as
> +	 * sizeof(rspn_req->name) is equal to max size of
> +	 * fc_host_symbolic_name(shost), but check anyway.
> +	 */
> +	if (len < 0)
> +		len = sizeof(rspn_req->name) - 1;

I'd rather have a compile-time check, whether the array sizes of
`rspn_req->name` and `fc_host_symbolic_name(shost)` run out of sync, or
against our expectations.

Something like:

	len = strscpy(rspn_req->name, fc_host_symbolic_name(shost),
		      sizeof(rspn_req->name));
	BUILD_BUG_ON(sizeof(rspn_req->name) !=
			     sizeof(fc_host_symbolic_name(shost)) ||
		     sizeof(rspn_req->name) !=
			     1 << sizeof(rspn_req->rspn.fr_name_len) * 8);
	rspn_req->rspn.fr_name_len = len;

Then the last assignment should also be correct; and if something changes -
unexpectedly, because this follows a FC standard - we need to adapt the code
anyway I'd think.

Or am I missing something?

>	rspn_req->rspn.fr_name_len = len;
>  
>	sg_init_one(&fc_req->sg_req, rspn_req, sizeof(*rspn_req));
> -- 
> 2.34.1
> 

-- 
Best Regards, Benjamin Block        /        Linux on IBM Z Kernel Development
IBM Deutschland Research & Development GmbH    /   https://www.ibm.com/privacy
Vors. Aufs.-R.: Gregor Pillen         /         Geschäftsführung: David Faller
Sitz der Ges.: Böblingen     /    Registergericht: AmtsG Stuttgart, HRB 243294

Re: [PATCH] scsi: zfcp: Replace strlcpy() with strscpy()

Posted by Alexander Gordeev 2 years, 1 month ago

On Thu, Nov 16, 2023 at 11:14:35AM -0800, Kees Cook wrote:

Hi Kees,

> diff --git a/drivers/s390/scsi/zfcp_fc.c b/drivers/s390/scsi/zfcp_fc.c
> index 4f0d0e55f0d4..1a29f10767fc 100644
> --- a/drivers/s390/scsi/zfcp_fc.c
> +++ b/drivers/s390/scsi/zfcp_fc.c
> @@ -900,8 +900,15 @@ static void zfcp_fc_rspn(struct zfcp_adapter *adapter,
>  	zfcp_fc_ct_ns_init(&rspn_req->ct_hdr, FC_NS_RSPN_ID,
>  			   FC_SYMBOLIC_NAME_SIZE);
>  	hton24(rspn_req->rspn.fr_fid.fp_fid, fc_host_port_id(shost));
> -	len = strlcpy(rspn_req->rspn.fr_name, fc_host_symbolic_name(shost),
> -		      FC_SYMBOLIC_NAME_SIZE);
> +	len = strscpy(rspn_req->name, fc_host_symbolic_name(shost),
> +		      sizeof(rspn_req->name));

Could you please explain why do you copy to rspn_req->name instead
of rspn_req->rspn.fr_name?

> +	/*
> +	 * It should be impossible for this to truncate, as
> +	 * sizeof(rspn_req->name) is equal to max size of
> +	 * fc_host_symbolic_name(shost), but check anyway.
> +	 */
> +	if (len < 0)
> +		len = sizeof(rspn_req->name) - 1;
>  	rspn_req->rspn.fr_name_len = len;
>  
>  	sg_init_one(&fc_req->sg_req, rspn_req, sizeof(*rspn_req));

Thanks!

Re: [PATCH] scsi: zfcp: Replace strlcpy() with strscpy()

Posted by Alexander Gordeev 2 years, 1 month ago

On Fri, Nov 17, 2023 at 07:19:48PM +0100, Alexander Gordeev wrote:
> > @@ -900,8 +900,15 @@ static void zfcp_fc_rspn(struct zfcp_adapter *adapter,
> >  	zfcp_fc_ct_ns_init(&rspn_req->ct_hdr, FC_NS_RSPN_ID,
> >  			   FC_SYMBOLIC_NAME_SIZE);
> >  	hton24(rspn_req->rspn.fr_fid.fp_fid, fc_host_port_id(shost));
> > -	len = strlcpy(rspn_req->rspn.fr_name, fc_host_symbolic_name(shost),
> > -		      FC_SYMBOLIC_NAME_SIZE);
> > +	len = strscpy(rspn_req->name, fc_host_symbolic_name(shost),
> > +		      sizeof(rspn_req->name));
> 
> Could you please explain why do you copy to rspn_req->name instead
> of rspn_req->rspn.fr_name?

Please, ignore this (stupid Friday evening) quesiton.

Although the use of sizeof() is right thing, FC_SYMBOLIC_NAME_SIZE
is so ubiquotous in this source that it probably makes sense to
address in a separate cleanup.

@Steffen, @Benjamin, could you please comment in this and below?

> > +	/*
> > +	 * It should be impossible for this to truncate, as
> > +	 * sizeof(rspn_req->name) is equal to max size of
> > +	 * fc_host_symbolic_name(shost), but check anyway.
> > +	 */
> > +	if (len < 0)
> > +		len = sizeof(rspn_req->name) - 1;

Not sure if this check is really needed. It could have been done
for strlcpy() also, but as you say - should not ever happen.

> >  	rspn_req->rspn.fr_name_len = len;
> >  
> >  	sg_init_one(&fc_req->sg_req, rspn_req, sizeof(*rspn_req));

Thanks!