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Date: Thu, 15 Apr 2021 12:58:07 -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 v3 2/2] wl3501_cs: Fix out-of-bounds warnings in
wl3501_mgmt_join
On Wed, Apr 14, 2021 at 06:45:15PM -0500, Gustavo A. R. Silva wrote:
> Fix the following out-of-bounds warnings by adding a new structure
> wl3501_req instead of duplicating the same members in structure
> wl3501_join_req and wl3501_scan_confirm:
>
> 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]
> arch/x86/include/asm/string_32.h:182:25: warning: '__builtin_memcpy' offset [25, 95] from the object at 'sig' is out of the bounds of referenced subobject 'beacon_period' with type 'short unsigned int' at offset 22 [-Warray-bounds]
>
> Refactor the code, accordingly:
>
> $ pahole -C wl3501_req drivers/net/wireless/wl3501_cs.o
> struct wl3501_req {
> u16 beacon_period; /* 0 2 */
> u16 dtim_period; /* 2 2 */
> u16 cap_info; /* 4 2 */
> u8 bss_type; /* 6 1 */
> u8 bssid[6]; /* 7 6 */
> struct iw_mgmt_essid_pset ssid; /* 13 34 */
> struct iw_mgmt_ds_pset ds_pset; /* 47 3 */
> struct iw_mgmt_cf_pset cf_pset; /* 50 8 */
> struct iw_mgmt_ibss_pset ibss_pset; /* 58 4 */
> struct iw_mgmt_data_rset bss_basic_rset; /* 62 10 */
>
> /* size: 72, cachelines: 2, members: 10 */
> /* last cacheline: 8 bytes */
> };
>
> $ 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 wl3501_req req; /* 36 72 */
>
> /* size: 108, cachelines: 2, members: 10 */
> /* last cacheline: 44 bytes */
> };
>
> $ pahole -C wl3501_scan_confirm drivers/net/wireless/wl3501_cs.o
> struct wl3501_scan_confirm {
> u16 next_blk; /* 0 2 */
> u8 sig_id; /* 2 1 */
> u8 reserved; /* 3 1 */
> u16 status; /* 4 2 */
> char timestamp[8]; /* 6 8 */
> char localtime[8]; /* 14 8 */
> struct wl3501_req req; /* 22 72 */
> /* --- cacheline 1 boundary (64 bytes) was 30 bytes ago --- */
> u8 rssi; /* 94 1 */
>
> /* size: 96, cachelines: 2, members: 8 */
> /* padding: 1 */
> /* last cacheline: 32 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 wl3501_req enclosing all those adjacent
> members is introduced, memcpy() doesn't overrun the length of
> &sig.beacon_period and &this->bss_set[i].beacon_period, because the
> address of the new struct object _req_ is used as the destination,
> instead.
>
> This helps with the ongoing efforts to globally enable -Warray-bounds
> and get us closer to being able to tighten the FORTIFY_SOURCE routines
> on memcpy().
>
> Link: https://github.com/KSPP/linux/issues/109
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
Awesome! Thank you for this solution.
Reviewed-by: Kees Cook <keescook@...omium.org>
--
Kees Cook
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