diff mbox series

staging: rtl8723bs: Check for NULL header value

Message ID 20220113002001.3498383-1-keescook@chromium.org (mailing list archive)
State Changes Requested
Headers show
Series staging: rtl8723bs: Check for NULL header value | expand

Commit Message

Kees Cook Jan. 13, 2022, 12:20 a.m. UTC
When building with -Warray-bounds, the following warning is emitted:

In file included from ./include/linux/string.h:253,
                 from ./arch/x86/include/asm/page_32.h:22,
                 from ./arch/x86/include/asm/page.h:14,
                 from ./arch/x86/include/asm/thread_info.h:12,
                 from ./include/linux/thread_info.h:60,
                 from ./arch/x86/include/asm/preempt.h:7,
                 from ./include/linux/preempt.h:78,
                 from ./include/linux/rcupdate.h:27,
                 from ./include/linux/rculist.h:11,
                 from ./include/linux/sched/signal.h:5,
                 from ./drivers/staging/rtl8723bs/include/drv_types.h:17,
                 from drivers/staging/rtl8723bs/core/rtw_recv.c:7:
In function 'memcpy',
    inlined from 'wlanhdr_to_ethhdr' at drivers/staging/rtl8723bs/core/rtw_recv.c:1554:2:
./include/linux/fortify-string.h:41:33: warning: '__builtin_memcpy' offset [0, 5] is out of the bounds [0, 0] [-Warray-bounds]
   41 | #define __underlying_memcpy     __builtin_memcpy
      |                                 ^

This is because the compiler sees it is possible for "ptr" to be a NULL
value, and concludes that it has zero size and attempts to copy to it
would overflow. Instead, detect the NULL return and error out early.

Cc: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Phillip Potter <phil@philpotter.co.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Michael Straube <straube.linux@gmail.com>
Cc: Fabio Aiuto <fabioaiuto83@gmail.com>
Cc: linux-staging@lists.linux.dev
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/staging/rtl8723bs/core/rtw_recv.c | 3 +++
 1 file changed, 3 insertions(+)

Comments

Dan Carpenter Jan. 13, 2022, 4:41 a.m. UTC | #1
On Wed, Jan 12, 2022 at 04:20:01PM -0800, Kees Cook wrote:
> When building with -Warray-bounds, the following warning is emitted:
> 
> In file included from ./include/linux/string.h:253,
>                  from ./arch/x86/include/asm/page_32.h:22,
>                  from ./arch/x86/include/asm/page.h:14,
>                  from ./arch/x86/include/asm/thread_info.h:12,
>                  from ./include/linux/thread_info.h:60,
>                  from ./arch/x86/include/asm/preempt.h:7,
>                  from ./include/linux/preempt.h:78,
>                  from ./include/linux/rcupdate.h:27,
>                  from ./include/linux/rculist.h:11,
>                  from ./include/linux/sched/signal.h:5,
>                  from ./drivers/staging/rtl8723bs/include/drv_types.h:17,
>                  from drivers/staging/rtl8723bs/core/rtw_recv.c:7:
> In function 'memcpy',
>     inlined from 'wlanhdr_to_ethhdr' at drivers/staging/rtl8723bs/core/rtw_recv.c:1554:2:
> ./include/linux/fortify-string.h:41:33: warning: '__builtin_memcpy' offset [0, 5] is out of the bounds [0, 0] [-Warray-bounds]
>    41 | #define __underlying_memcpy     __builtin_memcpy
>       |                                 ^
> 
> This is because the compiler sees it is possible for "ptr" to be a NULL
> value,

It's not really possible though.  I bet it's just saying that because of
the NULL check in get_recvframe_data().  Meanwhile we already have
dereferenced "precvframe" so GCC should know that the NULL check can
never be true.

> and concludes that it has zero size and attempts to copy to it
> would overflow. Instead, detect the NULL return and error out early.
> 
> Cc: Larry Finger <Larry.Finger@lwfinger.net>
> Cc: Phillip Potter <phil@philpotter.co.uk>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Michael Straube <straube.linux@gmail.com>
> Cc: Fabio Aiuto <fabioaiuto83@gmail.com>
> Cc: linux-staging@lists.linux.dev
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  drivers/staging/rtl8723bs/core/rtw_recv.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/staging/rtl8723bs/core/rtw_recv.c b/drivers/staging/rtl8723bs/core/rtw_recv.c
> index 41bfca549c64..61135c49322b 100644
> --- a/drivers/staging/rtl8723bs/core/rtw_recv.c
> +++ b/drivers/staging/rtl8723bs/core/rtw_recv.c
> @@ -1513,6 +1513,9 @@ static signed int wlanhdr_to_ethhdr(union recv_frame *precvframe)
>  	u8 *ptr = get_recvframe_data(precvframe) ; /*  point to frame_ctrl field */
>  	struct rx_pkt_attrib *pattrib = &precvframe->u.hdr.attrib;
>  
> +	if (!ptr)
> +		return _FAIL;
> +

Can we put a comment to say /* Silence GCC false positive with -Warray-bounds */

We should have a standard comment so that we can grep for this ten years
from now an remove any outdated work arounds.

regards,
dan carpenter
Greg KH Jan. 13, 2022, 9:13 a.m. UTC | #2
On Wed, Jan 12, 2022 at 04:20:01PM -0800, Kees Cook wrote:
> When building with -Warray-bounds, the following warning is emitted:
> 
> In file included from ./include/linux/string.h:253,
>                  from ./arch/x86/include/asm/page_32.h:22,
>                  from ./arch/x86/include/asm/page.h:14,
>                  from ./arch/x86/include/asm/thread_info.h:12,
>                  from ./include/linux/thread_info.h:60,
>                  from ./arch/x86/include/asm/preempt.h:7,
>                  from ./include/linux/preempt.h:78,
>                  from ./include/linux/rcupdate.h:27,
>                  from ./include/linux/rculist.h:11,
>                  from ./include/linux/sched/signal.h:5,
>                  from ./drivers/staging/rtl8723bs/include/drv_types.h:17,
>                  from drivers/staging/rtl8723bs/core/rtw_recv.c:7:
> In function 'memcpy',
>     inlined from 'wlanhdr_to_ethhdr' at drivers/staging/rtl8723bs/core/rtw_recv.c:1554:2:
> ./include/linux/fortify-string.h:41:33: warning: '__builtin_memcpy' offset [0, 5] is out of the bounds [0, 0] [-Warray-bounds]
>    41 | #define __underlying_memcpy     __builtin_memcpy
>       |                                 ^
> 
> This is because the compiler sees it is possible for "ptr" to be a NULL
> value, and concludes that it has zero size and attempts to copy to it
> would overflow. Instead, detect the NULL return and error out early.
> 
> Cc: Larry Finger <Larry.Finger@lwfinger.net>
> Cc: Phillip Potter <phil@philpotter.co.uk>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Michael Straube <straube.linux@gmail.com>
> Cc: Fabio Aiuto <fabioaiuto83@gmail.com>
> Cc: linux-staging@lists.linux.dev
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  drivers/staging/rtl8723bs/core/rtw_recv.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/staging/rtl8723bs/core/rtw_recv.c b/drivers/staging/rtl8723bs/core/rtw_recv.c
> index 41bfca549c64..61135c49322b 100644
> --- a/drivers/staging/rtl8723bs/core/rtw_recv.c
> +++ b/drivers/staging/rtl8723bs/core/rtw_recv.c
> @@ -1513,6 +1513,9 @@ static signed int wlanhdr_to_ethhdr(union recv_frame *precvframe)
>  	u8 *ptr = get_recvframe_data(precvframe) ; /*  point to frame_ctrl field */
>  	struct rx_pkt_attrib *pattrib = &precvframe->u.hdr.attrib;
>  
> +	if (!ptr)
> +		return _FAIL;

This will never happen, so let's not paper over compiler issues with
stuff like this please.

As the call to get_recvframe_data() is only done in one place in this
driver (in all drivers that look like this as well), it can just be
replaced with the real code instead of the nonsensical test for NULL and
then the compiler should be happy.

I'll gladly take that fix instead of this one, as that would be the
correct solution here.

thanks,

greg k-h
Kees Cook Jan. 13, 2022, 6:29 p.m. UTC | #3
On Thu, Jan 13, 2022 at 10:13:46AM +0100, Greg Kroah-Hartman wrote:
> On Wed, Jan 12, 2022 at 04:20:01PM -0800, Kees Cook wrote:
> > When building with -Warray-bounds, the following warning is emitted:
> > 
> > In file included from ./include/linux/string.h:253,
> >                  from ./arch/x86/include/asm/page_32.h:22,
> >                  from ./arch/x86/include/asm/page.h:14,
> >                  from ./arch/x86/include/asm/thread_info.h:12,
> >                  from ./include/linux/thread_info.h:60,
> >                  from ./arch/x86/include/asm/preempt.h:7,
> >                  from ./include/linux/preempt.h:78,
> >                  from ./include/linux/rcupdate.h:27,
> >                  from ./include/linux/rculist.h:11,
> >                  from ./include/linux/sched/signal.h:5,
> >                  from ./drivers/staging/rtl8723bs/include/drv_types.h:17,
> >                  from drivers/staging/rtl8723bs/core/rtw_recv.c:7:
> > In function 'memcpy',
> >     inlined from 'wlanhdr_to_ethhdr' at drivers/staging/rtl8723bs/core/rtw_recv.c:1554:2:
> > ./include/linux/fortify-string.h:41:33: warning: '__builtin_memcpy' offset [0, 5] is out of the bounds [0, 0] [-Warray-bounds]
> >    41 | #define __underlying_memcpy     __builtin_memcpy
> >       |                                 ^
> > 
> > This is because the compiler sees it is possible for "ptr" to be a NULL
> > value, and concludes that it has zero size and attempts to copy to it
> > would overflow. Instead, detect the NULL return and error out early.
> > 
> > Cc: Larry Finger <Larry.Finger@lwfinger.net>
> > Cc: Phillip Potter <phil@philpotter.co.uk>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: Michael Straube <straube.linux@gmail.com>
> > Cc: Fabio Aiuto <fabioaiuto83@gmail.com>
> > Cc: linux-staging@lists.linux.dev
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> >  drivers/staging/rtl8723bs/core/rtw_recv.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/staging/rtl8723bs/core/rtw_recv.c b/drivers/staging/rtl8723bs/core/rtw_recv.c
> > index 41bfca549c64..61135c49322b 100644
> > --- a/drivers/staging/rtl8723bs/core/rtw_recv.c
> > +++ b/drivers/staging/rtl8723bs/core/rtw_recv.c
> > @@ -1513,6 +1513,9 @@ static signed int wlanhdr_to_ethhdr(union recv_frame *precvframe)
> >  	u8 *ptr = get_recvframe_data(precvframe) ; /*  point to frame_ctrl field */
> >  	struct rx_pkt_attrib *pattrib = &precvframe->u.hdr.attrib;
> >  
> > +	if (!ptr)
> > +		return _FAIL;
> 
> This will never happen, so let's not paper over compiler issues with
> stuff like this please.
> 
> As the call to get_recvframe_data() is only done in one place in this
> driver (in all drivers that look like this as well), it can just be
> replaced with the real code instead of the nonsensical test for NULL and
> then the compiler should be happy.
> 
> I'll gladly take that fix instead of this one, as that would be the
> correct solution here.

I changed it around, but it doesn't help. I assume this is because we
build with -fno-delete-null-pointer-checks, so the compiler continues
to assume it's possible for the incoming argument to be NULL.

Should I rearrange this to do a NULL check for precvframe before all the
assignments in addition to removing get_recvframe_data()?

-Kees
Greg KH Jan. 13, 2022, 6:51 p.m. UTC | #4
On Thu, Jan 13, 2022 at 10:29:04AM -0800, Kees Cook wrote:
> On Thu, Jan 13, 2022 at 10:13:46AM +0100, Greg Kroah-Hartman wrote:
> > On Wed, Jan 12, 2022 at 04:20:01PM -0800, Kees Cook wrote:
> > > When building with -Warray-bounds, the following warning is emitted:
> > > 
> > > In file included from ./include/linux/string.h:253,
> > >                  from ./arch/x86/include/asm/page_32.h:22,
> > >                  from ./arch/x86/include/asm/page.h:14,
> > >                  from ./arch/x86/include/asm/thread_info.h:12,
> > >                  from ./include/linux/thread_info.h:60,
> > >                  from ./arch/x86/include/asm/preempt.h:7,
> > >                  from ./include/linux/preempt.h:78,
> > >                  from ./include/linux/rcupdate.h:27,
> > >                  from ./include/linux/rculist.h:11,
> > >                  from ./include/linux/sched/signal.h:5,
> > >                  from ./drivers/staging/rtl8723bs/include/drv_types.h:17,
> > >                  from drivers/staging/rtl8723bs/core/rtw_recv.c:7:
> > > In function 'memcpy',
> > >     inlined from 'wlanhdr_to_ethhdr' at drivers/staging/rtl8723bs/core/rtw_recv.c:1554:2:
> > > ./include/linux/fortify-string.h:41:33: warning: '__builtin_memcpy' offset [0, 5] is out of the bounds [0, 0] [-Warray-bounds]
> > >    41 | #define __underlying_memcpy     __builtin_memcpy
> > >       |                                 ^
> > > 
> > > This is because the compiler sees it is possible for "ptr" to be a NULL
> > > value, and concludes that it has zero size and attempts to copy to it
> > > would overflow. Instead, detect the NULL return and error out early.
> > > 
> > > Cc: Larry Finger <Larry.Finger@lwfinger.net>
> > > Cc: Phillip Potter <phil@philpotter.co.uk>
> > > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > > Cc: Michael Straube <straube.linux@gmail.com>
> > > Cc: Fabio Aiuto <fabioaiuto83@gmail.com>
> > > Cc: linux-staging@lists.linux.dev
> > > Signed-off-by: Kees Cook <keescook@chromium.org>
> > > ---
> > >  drivers/staging/rtl8723bs/core/rtw_recv.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/drivers/staging/rtl8723bs/core/rtw_recv.c b/drivers/staging/rtl8723bs/core/rtw_recv.c
> > > index 41bfca549c64..61135c49322b 100644
> > > --- a/drivers/staging/rtl8723bs/core/rtw_recv.c
> > > +++ b/drivers/staging/rtl8723bs/core/rtw_recv.c
> > > @@ -1513,6 +1513,9 @@ static signed int wlanhdr_to_ethhdr(union recv_frame *precvframe)
> > >  	u8 *ptr = get_recvframe_data(precvframe) ; /*  point to frame_ctrl field */
> > >  	struct rx_pkt_attrib *pattrib = &precvframe->u.hdr.attrib;
> > >  
> > > +	if (!ptr)
> > > +		return _FAIL;
> > 
> > This will never happen, so let's not paper over compiler issues with
> > stuff like this please.
> > 
> > As the call to get_recvframe_data() is only done in one place in this
> > driver (in all drivers that look like this as well), it can just be
> > replaced with the real code instead of the nonsensical test for NULL and
> > then the compiler should be happy.
> > 
> > I'll gladly take that fix instead of this one, as that would be the
> > correct solution here.
> 
> I changed it around, but it doesn't help. I assume this is because we
> build with -fno-delete-null-pointer-checks, so the compiler continues
> to assume it's possible for the incoming argument to be NULL.

That's a broken compiler then.

> Should I rearrange this to do a NULL check for precvframe before all the
> assignments in addition to removing get_recvframe_data()?

If you walk the call-chain back, you will see that precvframe can't ever
be NULL here (which is why this code doesn't crash), so don't check for
something that is impossible to ever hit please just because the
compiler is broken.

thanks,

greg k-h
Kees Cook Jan. 15, 2022, 4:14 a.m. UTC | #5
On Thu, Jan 13, 2022 at 07:51:24PM +0100, Greg Kroah-Hartman wrote:
> On Thu, Jan 13, 2022 at 10:29:04AM -0800, Kees Cook wrote:
> > On Thu, Jan 13, 2022 at 10:13:46AM +0100, Greg Kroah-Hartman wrote:
> > > On Wed, Jan 12, 2022 at 04:20:01PM -0800, Kees Cook wrote:
> > > > When building with -Warray-bounds, the following warning is emitted:
> > > > 
> > > > In file included from ./include/linux/string.h:253,
> > > >                  from ./arch/x86/include/asm/page_32.h:22,
> > > >                  from ./arch/x86/include/asm/page.h:14,
> > > >                  from ./arch/x86/include/asm/thread_info.h:12,
> > > >                  from ./include/linux/thread_info.h:60,
> > > >                  from ./arch/x86/include/asm/preempt.h:7,
> > > >                  from ./include/linux/preempt.h:78,
> > > >                  from ./include/linux/rcupdate.h:27,
> > > >                  from ./include/linux/rculist.h:11,
> > > >                  from ./include/linux/sched/signal.h:5,
> > > >                  from ./drivers/staging/rtl8723bs/include/drv_types.h:17,
> > > >                  from drivers/staging/rtl8723bs/core/rtw_recv.c:7:
> > > > In function 'memcpy',
> > > >     inlined from 'wlanhdr_to_ethhdr' at drivers/staging/rtl8723bs/core/rtw_recv.c:1554:2:
> > > > ./include/linux/fortify-string.h:41:33: warning: '__builtin_memcpy' offset [0, 5] is out of the bounds [0, 0] [-Warray-bounds]
> > > >    41 | #define __underlying_memcpy     __builtin_memcpy
> > > >       |                                 ^
> > > > 
> > > > This is because the compiler sees it is possible for "ptr" to be a NULL
> > > > value, and concludes that it has zero size and attempts to copy to it
> > > > would overflow. Instead, detect the NULL return and error out early.
> > > > 
> > > > Cc: Larry Finger <Larry.Finger@lwfinger.net>
> > > > Cc: Phillip Potter <phil@philpotter.co.uk>
> > > > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > > > Cc: Michael Straube <straube.linux@gmail.com>
> > > > Cc: Fabio Aiuto <fabioaiuto83@gmail.com>
> > > > Cc: linux-staging@lists.linux.dev
> > > > Signed-off-by: Kees Cook <keescook@chromium.org>
> > > > ---
> > > >  drivers/staging/rtl8723bs/core/rtw_recv.c | 3 +++
> > > >  1 file changed, 3 insertions(+)
> > > > 
> > > > diff --git a/drivers/staging/rtl8723bs/core/rtw_recv.c b/drivers/staging/rtl8723bs/core/rtw_recv.c
> > > > index 41bfca549c64..61135c49322b 100644
> > > > --- a/drivers/staging/rtl8723bs/core/rtw_recv.c
> > > > +++ b/drivers/staging/rtl8723bs/core/rtw_recv.c
> > > > @@ -1513,6 +1513,9 @@ static signed int wlanhdr_to_ethhdr(union recv_frame *precvframe)
> > > >  	u8 *ptr = get_recvframe_data(precvframe) ; /*  point to frame_ctrl field */
> > > >  	struct rx_pkt_attrib *pattrib = &precvframe->u.hdr.attrib;
> > > >  
> > > > +	if (!ptr)
> > > > +		return _FAIL;
> > > 
> > > This will never happen, so let's not paper over compiler issues with
> > > stuff like this please.
> > > 
> > > As the call to get_recvframe_data() is only done in one place in this
> > > driver (in all drivers that look like this as well), it can just be
> > > replaced with the real code instead of the nonsensical test for NULL and
> > > then the compiler should be happy.
> > > 
> > > I'll gladly take that fix instead of this one, as that would be the
> > > correct solution here.
> > 
> > I changed it around, but it doesn't help. I assume this is because we
> > build with -fno-delete-null-pointer-checks, so the compiler continues
> > to assume it's possible for the incoming argument to be NULL.
> 
> That's a broken compiler then.
> 
> > Should I rearrange this to do a NULL check for precvframe before all the
> > assignments in addition to removing get_recvframe_data()?
> 
> If you walk the call-chain back, you will see that precvframe can't ever
> be NULL here (which is why this code doesn't crash), so don't check for
> something that is impossible to ever hit please just because the
> compiler is broken.

I agree that the _original_ precvframe is always non-NULL, but the pointer
landing at memcpy() gets updated along the way. It seems the new problem
is that recvframe_pull() may return NULL and nothing is checking for that.
Adding this silences the warning:

diff --git a/drivers/staging/r8188eu/core/rtw_recv.c b/drivers/staging/r8188eu/core/rtw_recv.c
index 49a02d6239d6..946e659ae97a 100644
--- a/drivers/staging/r8188eu/core/rtw_recv.c
+++ b/drivers/staging/r8188eu/core/rtw_recv.c
@@ -1223,10 +1223,14 @@ static int wlanhdr_to_ethhdr(struct recv_frame *precvframe)
 		eth_type = 0x8712;
 		/*  append rx status for mp test packets */
 		ptr = recvframe_pull(precvframe, (rmv_len - sizeof(struct ethhdr) + 2) - 24);
+		if (!ptr)
+			return _FAIL;
 		memcpy(ptr, get_rxmem(precvframe), 24);
 		ptr += 24;
 	} else {
 		ptr = recvframe_pull(precvframe, (rmv_len - sizeof(struct ethhdr) + (bsnaphdr ? 2 : 0)));
+		if (!ptr)
+			return _FAIL;
 	}
 
 	memcpy(ptr, pattrib->dst, ETH_ALEN);

> 
> thanks,
> 
> greg k-h
diff mbox series

Patch

diff --git a/drivers/staging/rtl8723bs/core/rtw_recv.c b/drivers/staging/rtl8723bs/core/rtw_recv.c
index 41bfca549c64..61135c49322b 100644
--- a/drivers/staging/rtl8723bs/core/rtw_recv.c
+++ b/drivers/staging/rtl8723bs/core/rtw_recv.c
@@ -1513,6 +1513,9 @@  static signed int wlanhdr_to_ethhdr(union recv_frame *precvframe)
 	u8 *ptr = get_recvframe_data(precvframe) ; /*  point to frame_ctrl field */
 	struct rx_pkt_attrib *pattrib = &precvframe->u.hdr.attrib;
 
+	if (!ptr)
+		return _FAIL;
+
 	if (pattrib->encrypt)
 		recvframe_pull_tail(precvframe, pattrib->icv_len);