| Message ID | 1587819040-38793-1-git-send-email-xiyuyang19@fudan.edu.cn |
|---|---|
| State | Changes Requested |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | bpf: Fix sk_psock refcnt leak when receiving message | expand |
On Sat, Apr 25, 2020 at 02:50 PM CEST, Xiyu Yang wrote: > tcp_bpf_recvmsg() invokes sk_psock_get(), which returns a reference of > the specified sk_psock object to "psock" with increased refcnt. > > When tcp_bpf_recvmsg() returns, local variable "psock" becomes invalid, > so the refcount should be decreased to keep refcount balanced. > > The reference counting issue happens in several exception handling paths > of tcp_bpf_recvmsg(). When those error scenarios occur such as "flags" > includes MSG_ERRQUEUE, the function forgets to decrease the refcnt > increased by sk_psock_get(), causing a refcnt leak. > > Fix this issue by calling sk_psock_put() when those error scenarios > occur. > > Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn> > Signed-off-by: Xin Tan <tanxin.ctf@gmail.com> > --- > net/ipv4/tcp_bpf.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c > index 5a05327f97c1..feb6b90672c1 100644 > --- a/net/ipv4/tcp_bpf.c > +++ b/net/ipv4/tcp_bpf.c > @@ -265,11 +265,15 @@ static int tcp_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, > psock = sk_psock_get(sk); > if (unlikely(!psock)) > return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len); > - if (unlikely(flags & MSG_ERRQUEUE)) > + if (unlikely(flags & MSG_ERRQUEUE)) { > + sk_psock_put(sk, psock); > return inet_recv_error(sk, msg, len, addr_len); > + } > if (!skb_queue_empty(&sk->sk_receive_queue) && > - sk_psock_queue_empty(psock)) > + sk_psock_queue_empty(psock)) { > + sk_psock_put(sk, psock); > return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len); > + } > lock_sock(sk); > msg_bytes_ready: > copied = __tcp_bpf_recvmsg(sk, psock, msg, len, flags); Thanks for the fix. We can pull up the error queue read handling, that is the `flags & MSG_ERRQUEUE` branch, so that it happens before we grab a psock ref. The effect is the same because now, if we hit the !psock branch, tcp_recvmsg will first check if user wants to read the error queue anyway. That would translate to something like below, in addition to your changes. WDYT? ---8<--- diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c index 5a05327f97c1..99aa57bd1901 100644 --- a/net/ipv4/tcp_bpf.c +++ b/net/ipv4/tcp_bpf.c @@ -262,14 +262,17 @@ static int tcp_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, struct sk_psock *psock; int copied, ret; + if (unlikely(flags & MSG_ERRQUEUE)) + return inet_recv_error(sk, msg, len, addr_len); + psock = sk_psock_get(sk); if (unlikely(!psock)) return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len); - if (unlikely(flags & MSG_ERRQUEUE)) - return inet_recv_error(sk, msg, len, addr_len); if (!skb_queue_empty(&sk->sk_receive_queue) && sk_psock_queue_empty(psock)) return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len);
Jakub Sitnicki wrote: > On Sat, Apr 25, 2020 at 02:50 PM CEST, Xiyu Yang wrote: > > tcp_bpf_recvmsg() invokes sk_psock_get(), which returns a reference of > > the specified sk_psock object to "psock" with increased refcnt. > > > > When tcp_bpf_recvmsg() returns, local variable "psock" becomes invalid, > > so the refcount should be decreased to keep refcount balanced. > > > > The reference counting issue happens in several exception handling paths > > of tcp_bpf_recvmsg(). When those error scenarios occur such as "flags" > > includes MSG_ERRQUEUE, the function forgets to decrease the refcnt > > increased by sk_psock_get(), causing a refcnt leak. > > > > Fix this issue by calling sk_psock_put() when those error scenarios > > occur. > > > > Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn> > > Signed-off-by: Xin Tan <tanxin.ctf@gmail.com> > > --- Thanks Xiyu and Xin. Please add a Fixes tag, Fixes: e7a5f1f1cd000 ("bpf/sockmap: Read psock ingress_msg before sk_receive_queue") > > net/ipv4/tcp_bpf.c | 8 ++++++-- > > 1 file changed, 6 insertions(+), 2 deletions(-) > > > > diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c > > index 5a05327f97c1..feb6b90672c1 100644 > > --- a/net/ipv4/tcp_bpf.c > > +++ b/net/ipv4/tcp_bpf.c > > @@ -265,11 +265,15 @@ static int tcp_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, > > psock = sk_psock_get(sk); > > if (unlikely(!psock)) > > return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len); > > - if (unlikely(flags & MSG_ERRQUEUE)) > > + if (unlikely(flags & MSG_ERRQUEUE)) { > > + sk_psock_put(sk, psock); > > return inet_recv_error(sk, msg, len, addr_len); > > + } > > if (!skb_queue_empty(&sk->sk_receive_queue) && > > - sk_psock_queue_empty(psock)) > > + sk_psock_queue_empty(psock)) { > > + sk_psock_put(sk, psock); > > return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len); > > + } > > lock_sock(sk); > > msg_bytes_ready: > > copied = __tcp_bpf_recvmsg(sk, psock, msg, len, flags); > > Thanks for the fix. > > We can pull up the error queue read handling, that is the `flags & > MSG_ERRQUEUE` branch, so that it happens before we grab a psock ref. > > The effect is the same because now, if we hit the !psock branch, > tcp_recvmsg will first check if user wants to read the error queue > anyway. > > That would translate to something like below, in addition to your > changes. > > WDYT? Sure that seems slightly nicer to me. Xiyu do you mind sending a v2 with that change. Thanks again, John > > ---8<--- > > diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c > index 5a05327f97c1..99aa57bd1901 100644 > --- a/net/ipv4/tcp_bpf.c > +++ b/net/ipv4/tcp_bpf.c > @@ -262,14 +262,17 @@ static int tcp_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, > struct sk_psock *psock; > int copied, ret; > > + if (unlikely(flags & MSG_ERRQUEUE)) > + return inet_recv_error(sk, msg, len, addr_len); > + > psock = sk_psock_get(sk); > if (unlikely(!psock)) > return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len); > - if (unlikely(flags & MSG_ERRQUEUE)) > - return inet_recv_error(sk, msg, len, addr_len); > if (!skb_queue_empty(&sk->sk_receive_queue) && > sk_psock_queue_empty(psock)) > return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len);
diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c index 5a05327f97c1..feb6b90672c1 100644 --- a/net/ipv4/tcp_bpf.c +++ b/net/ipv4/tcp_bpf.c @@ -265,11 +265,15 @@ static int tcp_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, psock = sk_psock_get(sk); if (unlikely(!psock)) return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len); - if (unlikely(flags & MSG_ERRQUEUE)) + if (unlikely(flags & MSG_ERRQUEUE)) { + sk_psock_put(sk, psock); return inet_recv_error(sk, msg, len, addr_len); + } if (!skb_queue_empty(&sk->sk_receive_queue) && - sk_psock_queue_empty(psock)) + sk_psock_queue_empty(psock)) { + sk_psock_put(sk, psock); return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len); + } lock_sock(sk); msg_bytes_ready: copied = __tcp_bpf_recvmsg(sk, psock, msg, len, flags);