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Date: Wed, 7 Apr 2021 12:02:00 -0700
From: Kees Cook <keescook@...omium.org>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: linux-kernel@...r.kernel.org, Kalle Valo <kvalo@...eaurora.org>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 2/2][next] wl3501_cs: Fix out-of-bounds warning in
wl3501_mgmt_join
On Wed, Mar 31, 2021 at 04:45:34PM -0500, Gustavo A. R. Silva wrote:
> Fix the following out-of-bounds warning by enclosing
> some structure members into new struct req:
>
> arch/x86/include/asm/string_32.h:182:25: warning: '__builtin_memcpy' offset [39, 108] from the object at 'sig' is out of the bounds of referenced subobject 'beacon_period' with type 'short unsigned int' at offset 36 [-Warray-bounds]
>
> Refactor the code, accordingly:
>
> $ pahole -C wl3501_join_req drivers/net/wireless/wl3501_cs.o
> struct wl3501_join_req {
> u16 next_blk; /* 0 2 */
> u8 sig_id; /* 2 1 */
> u8 reserved; /* 3 1 */
> struct iw_mgmt_data_rset operational_rset; /* 4 10 */
> u16 reserved2; /* 14 2 */
> u16 timeout; /* 16 2 */
> u16 probe_delay; /* 18 2 */
> u8 timestamp[8]; /* 20 8 */
> u8 local_time[8]; /* 28 8 */
> struct {
> u16 beacon_period; /* 36 2 */
> u16 dtim_period; /* 38 2 */
> u16 cap_info; /* 40 2 */
> u8 bss_type; /* 42 1 */
> u8 bssid[6]; /* 43 6 */
> struct iw_mgmt_essid_pset ssid; /* 49 34 */
> /* --- cacheline 1 boundary (64 bytes) was 19 bytes ago --- */
> struct iw_mgmt_ds_pset ds_pset; /* 83 3 */
> struct iw_mgmt_cf_pset cf_pset; /* 86 8 */
> struct iw_mgmt_ibss_pset ibss_pset; /* 94 4 */
> struct iw_mgmt_data_rset bss_basic_rset; /* 98 10 */
> } req; /* 36 72 */
This section is the same as a large portion of struct wl3501_scan_confirm:
struct wl3501_scan_confirm {
u16 next_blk;
u8 sig_id;
u8 reserved;
u16 status;
char timestamp[8];
char localtime[8];
from here
u16 beacon_period;
u16 dtim_period;
u16 cap_info;
u8 bss_type;
u8 bssid[ETH_ALEN];
struct iw_mgmt_essid_pset ssid;
struct iw_mgmt_ds_pset ds_pset;
struct iw_mgmt_cf_pset cf_pset;
struct iw_mgmt_ibss_pset ibss_pset;
struct iw_mgmt_data_rset bss_basic_rset;
through here
u8 rssi;
};
It seems like maybe extracting that and using it in both structures
would make more sense?
>
> /* size: 108, cachelines: 2, members: 10 */
> /* last cacheline: 44 bytes */
> };
>
> The problem is that the original code is trying to copy data into a
> bunch of struct members adjacent to each other in a single call to
> memcpy(). Now that a new struct _req_ enclosing all those adjacent
> members is introduced, memcpy() doesn't overrun the length of
> &sig.beacon_period, because the address of the new struct object
> _req_ is used as the destination, instead.
>
> Also, this helps with the ongoing efforts to enable -Warray-bounds and
> avoid confusing the compiler.
>
> Link: https://github.com/KSPP/linux/issues/109
> Reported-by: kernel test robot <lkp@...el.com>
> Build-tested-by: kernel test robot <lkp@...el.com>
> Link: https://lore.kernel.org/lkml/60641d9b.2eNLedOGSdcSoAV2%25lkp@intel.com/
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
> Changes in v2:
> - None.
>
> drivers/net/wireless/wl3501.h | 22 ++++++++++++----------
> drivers/net/wireless/wl3501_cs.c | 4 ++--
> 2 files changed, 14 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/net/wireless/wl3501.h b/drivers/net/wireless/wl3501.h
> index ef9d605d8c88..774d8cac046d 100644
> --- a/drivers/net/wireless/wl3501.h
> +++ b/drivers/net/wireless/wl3501.h
> @@ -389,16 +389,18 @@ struct wl3501_join_req {
> u16 probe_delay;
> u8 timestamp[8];
> u8 local_time[8];
> - u16 beacon_period;
> - u16 dtim_period;
> - u16 cap_info;
> - u8 bss_type;
> - u8 bssid[ETH_ALEN];
> - struct iw_mgmt_essid_pset ssid;
> - struct iw_mgmt_ds_pset ds_pset;
> - struct iw_mgmt_cf_pset cf_pset;
> - struct iw_mgmt_ibss_pset ibss_pset;
> - struct iw_mgmt_data_rset bss_basic_rset;
> + struct {
> + u16 beacon_period;
> + u16 dtim_period;
> + u16 cap_info;
> + u8 bss_type;
> + u8 bssid[ETH_ALEN];
> + struct iw_mgmt_essid_pset ssid;
> + struct iw_mgmt_ds_pset ds_pset;
> + struct iw_mgmt_cf_pset cf_pset;
> + struct iw_mgmt_ibss_pset ibss_pset;
> + struct iw_mgmt_data_rset bss_basic_rset;
> + } req;
> };
>
> struct wl3501_join_confirm {
> diff --git a/drivers/net/wireless/wl3501_cs.c b/drivers/net/wireless/wl3501_cs.c
> index e149ef81d6cc..399d3bd2ae76 100644
> --- a/drivers/net/wireless/wl3501_cs.c
> +++ b/drivers/net/wireless/wl3501_cs.c
> @@ -590,7 +590,7 @@ static int wl3501_mgmt_join(struct wl3501_card *this, u16 stas)
> struct wl3501_join_req sig = {
> .sig_id = WL3501_SIG_JOIN_REQ,
> .timeout = 10,
> - .ds_pset = {
> + .req.ds_pset = {
> .el = {
> .id = IW_MGMT_INFO_ELEMENT_DS_PARAMETER_SET,
> .len = 1,
> @@ -599,7 +599,7 @@ static int wl3501_mgmt_join(struct wl3501_card *this, u16 stas)
> },
> };
>
> - memcpy(&sig.beacon_period, &this->bss_set[stas].beacon_period, 72);
> + memcpy(&sig.req, &this->bss_set[stas].beacon_period, sizeof(sig.req));
If not, then probably something like this should be added to make sure
nothing unexpected happens to change structure sizes:
BUILD_BUG_ON(sizeof(sig.req) != 72);
> return wl3501_esbq_exec(this, &sig, sizeof(sig));
> }
>
> --
> 2.27.0
>
--
Kees Cook
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