Re: [PATCH v2 2/2][next] wl3501_cs: Fix out-of-bounds warning in wl3501_mgmt_join
From: Gustavo A. R. Silva
Date: Tue Apr 13 2021 - 17:46:02 EST
Hi all!
On 4/7/21 14:02, Kees Cook wrote:
> 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?
If I do this, I would therefore have to make a bunch of other changes,
accordingly. I'm OK with that but I'd like to have the opinion of the
maintainers on all this. So, I will go and ping them from the cover
letter of this series with the hope that we can get some feedback from
them. :) They have been silent for a couple of weeks now.
>
>>
>> /* 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@xxxxxxxxx>
>> Build-tested-by: kernel test robot <lkp@xxxxxxxxx>
>> Link: https://lore.kernel.org/lkml/60641d9b.2eNLedOGSdcSoAV2%25lkp@xxxxxxxxx/
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
>> ---
>> 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);
Yep, this is sensible.
Thanks for the feedback!
--
Gustavo
>
>> return wl3501_esbq_exec(this, &sig, sizeof(sig));
>> }
>>
>> --
>> 2.27.0
>>
>