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 <[email protected]>
Signed-off-by: Xin Tan <[email protected]>
---
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);
--
2.7.4
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 <[email protected]>
> Signed-off-by: Xin Tan <[email protected]>
> ---
> 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 <[email protected]>
> > Signed-off-by: Xin Tan <[email protected]>
> > ---
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);