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[146.241.112.185]) by smtp.gmail.com with ESMTPSA id q12-20020a05600c46cc00b003b4ac05a8a4sm17696489wmo.27.2022.11.08.01.13.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Nov 2022 01:13:25 -0800 (PST) Message-ID: <9ffe152671d4620eb1bfd443699c3143db377ca3.camel@redhat.com> Subject: Re: [Patch net v2] kcm: close race conditions on sk_receive_queue From: Paolo Abeni To: Cong Wang , netdev@vger.kernel.org Cc: edumazet@google.com, Cong Wang , syzbot+278279efdd2730dd14bf@syzkaller.appspotmail.com, shaozhengchao , Tom Herbert Date: Tue, 08 Nov 2022 10:13:23 +0100 In-Reply-To: <20221103184620.359451-1-xiyou.wangcong@gmail.com> References: <20221103184620.359451-1-xiyou.wangcong@gmail.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.42.4 (3.42.4-2.fc35) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Hello, On Thu, 2022-11-03 at 11:46 -0700, Cong Wang wrote: > @@ -1085,53 +1085,17 @@ static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len) > return err; > } > > -static struct sk_buff *kcm_wait_data(struct sock *sk, int flags, > - long timeo, int *err) > -{ > - struct sk_buff *skb; > - > - while (!(skb = skb_peek(&sk->sk_receive_queue))) { > - if (sk->sk_err) { > - *err = sock_error(sk); > - return NULL; > - } > - > - if (sock_flag(sk, SOCK_DONE)) > - return NULL; It looks like skb_recv_datagram() ignores the SOCK_DONE flag, so this change could potentially miss some wait_data end coditions. On the flip side I don't see any place where the SOCK_DONE flag is set for the kcm socket, so this should be safe, but could you please document this in the commit message? [...] > @@ -1187,11 +1147,7 @@ static ssize_t kcm_splice_read(struct socket *sock, loff_t *ppos, > > /* Only support splice for SOCKSEQPACKET */ > > - timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT); > - > - lock_sock(sk); > - > - skb = kcm_wait_data(sk, flags, timeo, &err); > + skb = skb_recv_datagram(sk, flags, &err); > if (!skb) > goto err_out; > > @@ -1219,13 +1175,11 @@ static ssize_t kcm_splice_read(struct socket *sock, loff_t *ppos, > * finish reading the message. > */ > > - release_sock(sk); > - > + skb_free_datagram(sk, skb); > return copied; > > err_out: > - release_sock(sk); > - > + skb_free_datagram(sk, skb); We can reach here with skb == NULL and skb_free_datagram() -> __kfree_skb() -> skb_release_all() does not deal correctly with NULL skb, you need to check for skb explicitly here (or rearrange the error paths in a suitable way). Thanks! Paolo