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Sun, 29 Aug 2021 07:53:13 -0700 (PDT) Subject: Re: [syzbot] KASAN: use-after-free Write in sco_sock_timeout To: Hillf Danton Cc: linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org, luiz.von.dentz@intel.com, syzbot , syzkaller-bugs@googlegroups.com References: <000000000000b2725705ca78de29@google.com> <20210827011931.2323-1-hdanton@sina.com> <20210829082929.2897-1-hdanton@sina.com> From: Desmond Cheong Zhi Xi Message-ID: <11a30bc1-574f-aa1a-21d6-b886de9fc981@gmail.com> Date: Sun, 29 Aug 2021 22:53:10 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210829082929.2897-1-hdanton@sina.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 29/8/21 4:29 pm, Hillf Danton wrote: > On Fri, 27 Aug 2021 15:58:34 +0800 Desmond Cheong Zhi Xi wrote: >> On 27/8/21 9:19 am, Hillf Danton wrote: >>> On Thu, 26 Aug 2021 09:29:24 -0700 >>>> syzbot found the following issue on: >>>> >>>> HEAD commit: e3f30ab28ac8 Merge branch 'pktgen-samples-next' >>>> git tree: net-next >>>> console output: https://syzkaller.appspot.com/x/log.txt?x=13249c96300000 >>>> kernel config: https://syzkaller.appspot.com/x/.config?x=ef482942966bf763 >>>> dashboard link: https://syzkaller.appspot.com/bug?extid=2bef95d3ab4daa10155b >>>> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1 >>>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16a29ea9300000 >>>> >>>> The issue was bisected to: >>>> >>>> commit e1dee2c1de2b4dd00eb44004a4bda6326ed07b59 >>>> Author: Desmond Cheong Zhi Xi >>>> Date: Tue Aug 10 04:14:10 2021 +0000 >>>> >>>> Bluetooth: fix repeated calls to sco_sock_kill > > To fix the uaf, grab another hold to sock to make the timeout work safe. > > #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git e3f30ab28ac8 > > --- a/net/bluetooth/sco.c > +++ b/net/bluetooth/sco.c > @@ -190,15 +190,14 @@ static void sco_conn_del(struct hci_conn > sco_conn_unlock(conn); > > if (sk) { > - sock_hold(sk); > lock_sock(sk); > sco_sock_clear_timer(sk); > sco_chan_del(sk, err); > release_sock(sk); > - sock_put(sk); > > /* Ensure no more work items will run before freeing conn. */ > cancel_delayed_work_sync(&conn->timeout_work); > + sock_put(sk); Hi Hillf, Saw that this passed the reproducer. But on closer inspection, I think what's happening is that sco_conn_del is never run. So the extra sock_hold prevents a UAF, but that's because now the reference count never goes to 0. In my opinion, something closer to your previous proposal (+ also addressing other calls to __sco_sock_close) where we call cancel_delayed_work_sync after the channel is deleted would address the root cause better. Just my two cents. > } > > hcon->sco_data = NULL; > @@ -212,6 +211,8 @@ static void __sco_chan_add(struct sco_co > > sco_pi(sk)->conn = conn; > conn->sk = sk; > + /* make timeout_work safe; will be put in sco_conn_del() */ > + sock_hold(sk); > > INIT_DELAYED_WORK(&conn->timeout_work, sco_sock_timeout); > > -- >