Re: [PATCH] wifi: mac80211: fix oob in ieee80211_rx_mgmt_beacon

[Johannes Berg <johannes@sipsolutions.net>]

On Tue, 2025-06-17 at 12:41 +0800, Edward Adam Davis wrote:
> According to ieee80211_s1g_optional_len(), it can be clearly seen that the
> maximum size of variable is 4 and it is an array. Based on the above, the
> parsing of the frame control field and optional field is optimized.
> 
> Fixes: 1e1f706fc2ce ("wifi: cfg80211/mac80211: correctly parse S1G beacon optional elements")
> Reported-by: syzbot+6554b492c7008bcd3385@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=6554b492c7008bcd3385
> Tested-by: syzbot+6554b492c7008bcd3385@syzkaller.appspotmail.com
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
>  include/linux/ieee80211.h | 2 +-
>  net/mac80211/mlme.c       | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/ieee80211.h b/include/linux/ieee80211.h
> index ce377f7fb912..556ce95e0b0f 100644
> --- a/include/linux/ieee80211.h
> +++ b/include/linux/ieee80211.h
> @@ -1278,7 +1278,7 @@ struct ieee80211_ext {
>  			u8 sa[ETH_ALEN];
>  			__le32 timestamp;
>  			u8 change_seq;
> -			u8 variable[0];
> +			u8 variable[4];

That's incorrect when those fields aren't present, and will result in
wrong sizeof(). I believe the correct fix is one I sent before, to just
make it []:

https://lore.kernel.org/linux-wireless/20250614003037.a3e82e882251.I2e8b58e56ff2a9f8b06c66f036578b7c1d4e4685@changeid/

johannes