From: Eric Dumazet via Linux-kernel-mentees <linux-kernel-mentees@lists.linuxfoundation.org>
To: Siddh Raman Pant <code@siddh.me>
Cc: "Paul E. McKenney" <paulmck@kernel.org>,
netdev <netdev@vger.kernel.org>,
linux-wireless <linux-wireless@vger.kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Jakub Kicinski <kuba@kernel.org>,
Johannes Berg <johannes@sipsolutions.net>,
Paolo Abeni <pabeni@redhat.com>,
linux-kernel-mentees
<linux-kernel-mentees@lists.linuxfoundation.org>,
"David S . Miller" <davem@davemloft.net>
Subject: Re: [PATCH] net: Fix UAF in ieee80211_scan_rx()
Date: Tue, 26 Jul 2022 12:07:16 +0200 [thread overview]
Message-ID: <CANn89iLN27NWA7Stkr4ODp6V-Q-3em0dJ2JixDMNcNY7Ap5muA@mail.gmail.com> (raw)
In-Reply-To: <20220701145423.53208-1-code@siddh.me>
On Fri, Jul 1, 2022 at 4:55 PM Siddh Raman Pant <code@siddh.me> wrote:
>
> ieee80211_scan_rx() tries to access scan_req->flags after a null check
> (see line 303 of mac80211/scan.c), but ___cfg80211_scan_done() uses
> kfree() on the scan_req (see line 991 of wireless/scan.c).
>
> This results in a UAF.
>
> ieee80211_scan_rx() is called inside a RCU read-critical section
> initiated by ieee80211_rx_napi() (see line 5043 of mac80211/rx.c).
>
> Thus, add an rcu_head to the scan_req struct so as to use kfree_rcu()
> instead of kfree() so that we don't free during the critical section.
>
> Bug report (3): https://syzkaller.appspot.com/bug?extid=f9acff9bf08a845f225d
> Reported-by: syzbot+f9acff9bf08a845f225d@syzkaller.appspotmail.com
> Reported-by: syzbot+6cb476b7c69916a0caca@syzkaller.appspotmail.com
> Reported-by: syzbot+9250865a55539d384347@syzkaller.appspotmail.com
>
> Signed-off-by: Siddh Raman Pant <code@siddh.me>
> ---
> include/net/cfg80211.h | 2 ++
> net/wireless/scan.c | 2 +-
> 2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
> index 6d02e12e4702..ba4a49884de8 100644
> --- a/include/net/cfg80211.h
> +++ b/include/net/cfg80211.h
> @@ -2368,6 +2368,7 @@ struct cfg80211_scan_6ghz_params {
> * @n_6ghz_params: number of 6 GHz params
> * @scan_6ghz_params: 6 GHz params
> * @bssid: BSSID to scan for (most commonly, the wildcard BSSID)
> + * @rcu_head: (internal) RCU head to use for freeing
> */
> struct cfg80211_scan_request {
> struct cfg80211_ssid *ssids;
> @@ -2397,6 +2398,7 @@ struct cfg80211_scan_request {
> bool scan_6ghz;
> u32 n_6ghz_params;
> struct cfg80211_scan_6ghz_params *scan_6ghz_params;
> + struct rcu_head rcu_head;
>
> /* keep last */
> struct ieee80211_channel *channels[];
> diff --git a/net/wireless/scan.c b/net/wireless/scan.c
> index 6d82bd9eaf8c..638b2805222c 100644
> --- a/net/wireless/scan.c
> +++ b/net/wireless/scan.c
> @@ -988,7 +988,7 @@ void ___cfg80211_scan_done(struct cfg80211_registered_device *rdev,
> kfree(rdev->int_scan_req);
> rdev->int_scan_req = NULL;
>
> - kfree(rdev->scan_req);
> + kfree_rcu(rdev->scan_req, rcu_head);
> rdev->scan_req = NULL;
Note: this is slightly racy.
You are supposed to follow this order in this situation.
1) Clear the pointer
Then:
2) wait an rcu grace period (synchronize_rcu()) or use call_rcu()/kfree_rcu().
>
> if (!send_message)
> --
> 2.35.1
>
>
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next prev parent reply other threads:[~2022-07-26 10:07 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-01 14:54 [PATCH] net: Fix UAF in ieee80211_scan_rx() Siddh Raman Pant
2022-07-07 11:36 ` Ping: " Siddh Raman Pant via Linux-kernel-mentees
2022-07-07 11:50 ` Greg KH
2022-07-07 11:59 ` Siddh Raman Pant via Linux-kernel-mentees
2022-07-26 9:55 ` Kalle Valo
2022-07-26 11:50 ` Siddh Raman Pant via Linux-kernel-mentees
2022-07-26 10:07 ` Eric Dumazet via Linux-kernel-mentees [this message]
2022-07-26 12:16 ` Siddh Raman Pant via Linux-kernel-mentees
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