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[79.191.186.228]) by smtp.gmail.com with ESMTPSA id t73sm546930lff.135.2021.07.28.03.12.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Jul 2021 03:12:14 -0700 (PDT) References: <20210723183630.5088-1-xiyou.wangcong@gmail.com> User-agent: mu4e 1.1.0; emacs 27.2 From: Jakub Sitnicki To: Cong Wang Cc: netdev@vger.kernel.org, Cong Wang , Eric Dumazet , John Fastabend , Daniel Borkmann , Lorenz Bauer Subject: Re: [Patch bpf-next] unix_bpf: fix a potential deadlock in unix_dgram_bpf_recvmsg() In-reply-to: <20210723183630.5088-1-xiyou.wangcong@gmail.com> Date: Wed, 28 Jul 2021 12:12:13 +0200 Message-ID: <87h7ge3fya.fsf@cloudflare.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, Jul 23, 2021 at 08:36 PM CEST, Cong Wang wrote: > From: Cong Wang > > As Eric noticed, __unix_dgram_recvmsg() may acquire u->iolock > too, so we have to release it before calling this function. > > Fixes: 9825d866ce0d ("af_unix: Implement unix_dgram_bpf_recvmsg()") > Reported-by: Eric Dumazet > Cc: John Fastabend > Cc: Daniel Borkmann > Cc: Jakub Sitnicki > Cc: Lorenz Bauer > Signed-off-by: Cong Wang > --- > net/unix/unix_bpf.c | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > diff --git a/net/unix/unix_bpf.c b/net/unix/unix_bpf.c > index db0cda29fb2f..b07cb30e87b1 100644 > --- a/net/unix/unix_bpf.c > +++ b/net/unix/unix_bpf.c > @@ -53,8 +53,9 @@ static int unix_dgram_bpf_recvmsg(struct sock *sk, struct msghdr *msg, > mutex_lock(&u->iolock); > if (!skb_queue_empty(&sk->sk_receive_queue) && > sk_psock_queue_empty(psock)) { > - ret = __unix_dgram_recvmsg(sk, msg, len, flags); > - goto out; > + mutex_unlock(&u->iolock); > + sk_psock_put(sk, psock); > + return __unix_dgram_recvmsg(sk, msg, len, flags); > } > > msg_bytes_ready: > @@ -68,13 +69,13 @@ static int unix_dgram_bpf_recvmsg(struct sock *sk, struct msghdr *msg, > if (data) { > if (!sk_psock_queue_empty(psock)) > goto msg_bytes_ready; > - ret = __unix_dgram_recvmsg(sk, msg, len, flags); > - goto out; > + mutex_unlock(&u->iolock); > + sk_psock_put(sk, psock); > + return __unix_dgram_recvmsg(sk, msg, len, flags); > } > copied = -EAGAIN; > } > ret = copied; > -out: > mutex_unlock(&u->iolock); > sk_psock_put(sk, psock); > return ret; Nit: Can be just `return copied`. `ret` became useless. Acked-by: Jakub Sitnicki