Subject: Re: [PATCH v2 2/5] treewide: Replace open-coded flex arrays in unions

From: Kees Cook <[email-masked]>
Date: Fri, 27 Aug 2021 09:08:19 -0700

On Thu, Aug 26, 2021 at 08:24:52AM +0200, Marc Kleine-Budde wrote:
> On 25.08.2021 22:04:55, Kees Cook wrote:
> > In support of enabling -Warray-bounds and -Wzero-length-bounds and
> > correctly handling run-time memcpy() bounds checking, replace all
> > open-coded flexible arrays (i.e. 0-element arrays) in unions with the
> > flex_array() helper macro.
> > 
> > This fixes warnings such as:
> > 
> > fs/hpfs/anode.c: In function 'hpfs_add_sector_to_btree':
> > fs/hpfs/anode.c:209:27: warning: array subscript 0 is outside the bounds of an interior zero-length array 'struct bplus_internal_node[0]' [-Wzero-length-bounds]
> >   209 |    anode->btree.u.internal[0].down = cpu_to_le32(a);
> >       |    ~~~~~~~~~~~~~~~~~~~~~~~^~~
> > In file included from fs/hpfs/hpfs_fn.h:26,
> >                  from fs/hpfs/anode.c:10:
> > fs/hpfs/hpfs.h:412:32: note: while referencing 'internal'
> >   412 |     struct bplus_internal_node internal[0]; /* (internal) 2-word entries giving
> >       |                                ^~~~~~~~
> > 
> > drivers/net/can/usb/etas_es58x/es58x_fd.c: In function 'es58x_fd_tx_can_msg':
> > drivers/net/can/usb/etas_es58x/es58x_fd.c:360:35: warning: array subscript 65535 is outside the bounds of an interior zero-length array 'u8[0]' {aka 'unsigned char[]'} [-Wzero-length-bounds]
> >   360 |  tx_can_msg = (typeof(tx_can_msg))&es58x_fd_urb_cmd->raw_msg[msg_len];
> >       |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > In file included from drivers/net/can/usb/etas_es58x/es58x_core.h:22,
> >                  from drivers/net/can/usb/etas_es58x/es58x_fd.c:17:
> > drivers/net/can/usb/etas_es58x/es58x_fd.h:231:6: note: while referencing 'raw_msg'
> >   231 |   u8 raw_msg[0];
> >       |      ^~~~~~~
> > 
> > Cc: "Gustavo A. R. Silva" <[email-masked]>
> > Cc: Arnd Bergmann <[email-masked]>
> > Cc: Ayush Sawal <[email-masked]>
> > Cc: Vinay Kumar Yadav <[email-masked]>
> > Cc: Rohit Maheshwari <[email-masked]>
> > Cc: Herbert Xu <[email-masked]>
> > Cc: "David S. Miller" <[email-masked]>
> > Cc: Kalle Valo <[email-masked]>
> > Cc: Jakub Kicinski <[email-masked]>
> > Cc: Stanislaw Gruszka <[email-masked]>
> > Cc: Luca Coelho <[email-masked]>
> > Cc: "James E.J. Bottomley" <[email-masked]>
> > Cc: "Martin K. Petersen" <[email-masked]>
> > Cc: Alexei Starovoitov <[email-masked]>
> > Cc: Daniel Borkmann <[email-masked]>
> > Cc: Andrii Nakryiko <[email-masked]>
> > Cc: Martin KaFai Lau <[email-masked]>
> > Cc: Song Liu <[email-masked]>
> > Cc: Yonghong Song <[email-masked]>
> > Cc: John Fastabend <[email-masked]>
> > Cc: KP Singh <[email-masked]>
> > Cc: Johannes Berg <[email-masked]>
> > Cc: Mordechay Goodstein <[email-masked]>
> > Cc: Lee Jones <[email-masked]>
> > Cc: Wolfgang Grandegger <[email-masked]>
> > Cc: Marc Kleine-Budde <[email-masked]>
> > Cc: Arunachalam Santhanam <[email-masked]>
> > Cc: Vincent Mailhol <[email-masked]>
> > Cc: Mikulas Patocka <[email-masked]>
> > Cc: [email-masked]
> > Cc: [email-masked]
> > Cc: [email-masked]
> > Cc: [email-masked]
> > Cc: [email-masked]
> > Cc: [email-masked]
> > Cc: [email-masked]
> > Signed-off-by: Kees Cook <[email-masked]>
> > ---
> >  drivers/net/can/usb/etas_es58x/es581_4.h          |  2 +-
> >  drivers/net/can/usb/etas_es58x/es58x_fd.h         |  2 +-
> 
> For the can drivers:
> 
> Acked-by: Marc Kleine-Budde <[email-masked]>

Thanks!

> BTW: Is there opportunity for conversion, too?
> 
> | drivers/net/can/peak_canfd/peak_pciefd_main.c:146:32: warning: array of flexible structures

Oh, hrmpf. This isn't a sane use of flex arrays:

struct __packed pucan_rx_msg {
	...
	__le32	can_id;
	u8	d[];
};

struct pciefd_rx_dma {
        __le32 irq_status;
        __le32 sys_time_low;
        __le32 sys_time_high;
        struct pucan_rx_msg msg[];
} __packed __aligned(4);

I think that needs to be handled separately. How are you building to get
that warning, by the way? I haven't seen that in my builds...

-- 
Kees Cook