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[73.241.150.58]) by smtp.gmail.com with ESMTPSA id j4sm5998656pfg.133.2020.03.20.10.10.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 20 Mar 2020 10:10:40 -0700 (PDT) Subject: Re: [PATCH v3] sctp: fix refcount bug in sctp_wfree To: Qiujun Huang , marcelo.leitner@gmail.com, davem@davemloft.net Cc: vyasevich@gmail.com, nhorman@tuxdriver.com, kuba@kernel.org, linux-sctp@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, anenbupt@gmail.com References: <20200320110959.2114-1-hqjagain@gmail.com> From: Eric Dumazet Message-ID: <2dc8673f-a46d-1438-95a8-cfb455bbea57@gmail.com> Date: Fri, 20 Mar 2020 10:10:38 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200320110959.2114-1-hqjagain@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/20/20 4:09 AM, Qiujun Huang wrote: > Do accounting for skb's real sk. > In some case skb->sk != asoc->base.sk: > > for the trouble SKB, it was in outq->transmitted queue > > sctp_outq_sack > sctp_check_transmitted > SKB was moved to outq->sack > then throw away the sack queue > SKB was deleted from outq->sack > (but the datamsg held SKB at sctp_datamsg_to_asoc > So, sctp_wfree was not called to destroy SKB) > > then migrate happened > > sctp_for_each_tx_datachunk( > sctp_clear_owner_w); > sctp_assoc_migrate(); > sctp_for_each_tx_datachunk( > sctp_set_owner_w); > SKB was not in the outq, and was not changed to newsk > > finally > > __sctp_outq_teardown > sctp_chunk_put (for another skb) > sctp_datamsg_put > __kfree_skb(msg->frag_list) > sctp_wfree (for SKB) > this case in sctp_wfree SKB->sk was oldsk. > > It looks only trouble here so handling it in sctp_wfree is enough. > > Reported-and-tested-by: syzbot+cea71eec5d6de256d54d@syzkaller.appspotmail.com > Signed-off-by: Qiujun Huang > --- > net/sctp/socket.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/net/sctp/socket.c b/net/sctp/socket.c > index 1b56fc440606..5f5c28b30e25 100644 > --- a/net/sctp/socket.c > +++ b/net/sctp/socket.c > @@ -9080,7 +9080,7 @@ static void sctp_wfree(struct sk_buff *skb) > { > struct sctp_chunk *chunk = skb_shinfo(skb)->destructor_arg; > struct sctp_association *asoc = chunk->asoc; > - struct sock *sk = asoc->base.sk; > + struct sock *sk = skb->sk; > > sk_mem_uncharge(sk, skb->truesize); > sk->sk_wmem_queued -= skb->truesize + sizeof(struct sctp_chunk); > @@ -9109,7 +9109,7 @@ static void sctp_wfree(struct sk_buff *skb) > } > > sock_wfree(skb); > - sctp_wake_up_waiters(sk, asoc); > + sctp_wake_up_waiters(asoc->base.sk, asoc); > > sctp_association_put(asoc); > } > This does not really solve the issue. Even if the particular syzbot repro is now fine. Really, having anything _after_ the sock_wfree(skb) is the bug, since the current thread no longer own a reference on a socket.