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

Kees Cook
2021-08-27T16:08:28Z

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" <gustavoars@kernel.org>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Ayush Sawal <ayush.sawal@chelsio.com>
> > Cc: Vinay Kumar Yadav <vinay.yadav@chelsio.com>
> > Cc: Rohit Maheshwari <rohitm@chelsio.com>
> > Cc: Herbert Xu <herbert@gondor.apana.org.au>
> > Cc: "David S. Miller" <davem@davemloft.net>
> > Cc: Kalle Valo <kvalo@codeaurora.org>
> > Cc: Jakub Kicinski <kuba@kernel.org>
> > Cc: Stanislaw Gruszka <stf_xl@wp.pl>
> > Cc: Luca Coelho <luciano.coelho@intel.com>
> > Cc: "James E.J. Bottomley" <jejb@linux.ibm.com>
> > Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
> > Cc: Alexei Starovoitov <ast@kernel.org>
> > Cc: Daniel Borkmann <daniel@iogearbox.net>
> > Cc: Andrii Nakryiko <andrii@kernel.org>
> > Cc: Martin KaFai Lau <kafai@fb.com>
> > Cc: Song Liu <songliubraving@fb.com>
> > Cc: Yonghong Song <yhs@fb.com>
> > Cc: John Fastabend <john.fastabend@gmail.com>
> > Cc: KP Singh <kpsingh@kernel.org>
> > Cc: Johannes Berg <johannes.berg@intel.com>
> > Cc: Mordechay Goodstein <mordechay.goodstein@intel.com>
> > Cc: Lee Jones <lee.jones@linaro.org>
> > Cc: Wolfgang Grandegger <wg@grandegger.com>
> > Cc: Marc Kleine-Budde <mkl@pengutronix.de>
> > Cc: Arunachalam Santhanam <arunachalam.santhanam@in.bosch.com>
> > Cc: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
> > Cc: Mikulas Patocka <mikulas@artax.karlin.mff.cuni.cz>
> > Cc: linux-crypto@vger.kernel.org
> > Cc: ath10k@lists.infradead.org
> > Cc: linux-wireless@vger.kernel.org
> > Cc: netdev@vger.kernel.org
> > Cc: linux-scsi@vger.kernel.org
> > Cc: linux-can@vger.kernel.org
> > Cc: bpf@vger.kernel.org
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> > 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 <mkl@pengutronix.de>

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