From: Shuah Khan <skhan@linuxfoundation.org>
To: Du Cheng <ducheng2@gmail.com>,
Thomas Pedersen <thomas@adapt-ip.com>,
Johannes Berg <johannes@sipsolutions.net>
Cc: linux-wireless@vger.kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
syzbot+405843667e93b9790fc1@syzkaller.appspotmail.com,
Shuah Khan <skhan@linuxfoundation.org>
Subject: Re: [PATCH] net: mac80211: fix hard-coding of length check on skb->len in ieee80211_scan_rx()
Date: Tue, 11 May 2021 16:29:07 -0600 [thread overview]
Message-ID: <e52ff0a3-7b64-037d-7825-9cbbcafa21b6@linuxfoundation.org> (raw)
In-Reply-To: <20210510041649.589754-1-ducheng2@gmail.com>
On 5/9/21 10:16 PM, Du Cheng wrote:
> Replace hard-coding with compile-time constants for header length
> check on skb->len. This skb->len will be checked again further down the
> callstack in cfg80211_inform_bss_frame_data() in net/wireless/scan.c
> (which has a proper length check with WARN_ON()). If the kernel is
> configure to panic_on_warn(), the insuffient check of skb->len in
> ieee80211_scan_rx() causes kernel crash in
> cfg80211_inform_bss_frame_data().
>
Where is this WARN_ON? I didn't see it cfg80211_inform_bss_frame_data()
Please add more information on why the values of min_hdr_len in this
patch make sense for each of these cases.
> Bug reported by syzbot:
> https://syzkaller.appspot.com/bug?id=183869c2f25b1c8692e381d8fcd69771a99221cc
>
> Reported-by: syzbot+405843667e93b9790fc1@syzkaller.appspotmail.com
> Signed-off-by: Du Cheng <ducheng2@gmail.com>
> ---
>
> This patch has passed syzbot testing.
>
> net/mac80211/scan.c | 18 +++++++++++++-----
> 1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/net/mac80211/scan.c b/net/mac80211/scan.c
> index d4cc9ac2d703..562eda13e802 100644
> --- a/net/mac80211/scan.c
> +++ b/net/mac80211/scan.c
> @@ -251,13 +251,21 @@ void ieee80211_scan_rx(struct ieee80211_local *local, struct sk_buff *skb)
> struct ieee80211_mgmt *mgmt = (void *)skb->data;
> struct ieee80211_bss *bss;
> struct ieee80211_channel *channel;
> + size_t min_hdr_len = offsetof(struct ieee80211_mgmt, u.probe_resp.variable);
> +
> + if (!ieee80211_is_probe_resp(mgmt->frame_control) &&
> + !ieee80211_is_beacon(mgmt->frame_control) &&
> + !ieee80211_is_s1g_beacon(mgmt->frame_control))
> + return;
>
Is the above check necessary? This doesn't look right. This skips
the ieee80211_is_s1g_beacon() all together.
if (ieee80211_is_s1g_beacon(mgmt->frame_control)) {
> - if (skb->len < 15)
> - return;
Why not compare the header offset you expect here instead of 15 and
return?
> - } else if (skb->len < 24 ||
Can you explain why it makes sense to remove < 24 check?
> - (!ieee80211_is_probe_resp(mgmt->frame_control) &&
> - !ieee80211_is_beacon(mgmt->frame_control)))
> + if (ieee80211_is_s1g_short_beacon(mgmt->frame_control))
> + min_hdr_len = offsetof(struct ieee80211_ext, u.s1g_short_beacon.variable);
> + else
> + min_hdr_len = offsetof(struct ieee80211_ext, u.s1g_beacon);
> + }
> +
> + if (skb->len < min_hdr_len)
> return;
>
> sdata1 = rcu_dereference(local->scan_sdata);
>
thanks,
-- Shuah
next prev parent reply other threads:[~2021-05-11 22:29 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-10 4:16 [PATCH] net: mac80211: fix hard-coding of length check on skb->len in ieee80211_scan_rx() Du Cheng
2021-05-11 22:29 ` Shuah Khan [this message]
2021-05-12 0:55 ` Du Cheng
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