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Date: Fri, 15 Jan 2016 19:40:39 -0200
From: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To: netdev@...r.kernel.org
Cc: linux-sctp@...r.kernel.org, dvyukov@...gle.com,
vyasevich@...il.com, eric.dumazet@...il.com,
syzkaller@...glegroups.com, kcc@...gle.com, glider@...gle.com,
sasha.levin@...cle.com
Subject: [PATCH net] sctp: do sanity checks before migrating the asoc
On Fri, Jan 15, 2016 at 08:11:03PM +0100, Dmitry Vyukov wrote:
> On Fri, Jan 15, 2016 at 7:46 PM, Marcelo Ricardo Leitner
> <marcelo.leitner@...il.com> wrote:
> > On Wed, Dec 30, 2015 at 09:42:27PM +0100, Dmitry Vyukov wrote:
> >> Hello,
> >>
> >> The following program leads to a leak of two sock objects:
> > ...
> >>
> >> On commit 8513342170278468bac126640a5d2d12ffbff106 (Dec 28).
> >
> > I'm afraid I cannot reproduce this one?
> > I enabled dynprintk at sctp_destroy_sock and it does print twice when I
> > run this test app.
> > Also added debugs to check association lifetime, and then it was
> > destroyed. Same for endpoint.
> >
> > Checking with trace-cmd, both calls to sctp_close() resulted in
> > sctp_destroy_sock() being called.
> >
> > As for sock_hold/put, they are matched too.
> >
> > Ideas? Log is below for double checking
>
>
> Hummm... I can reproduce it pretty reliably.
>
> [ 197.459024] kmemleak: 11 new suspected memory leaks (see
> /sys/kernel/debug/kmemleak)
> [ 307.494874] kmemleak: 409 new suspected memory leaks (see
> /sys/kernel/debug/kmemleak)
> [ 549.784022] kmemleak: 125 new suspected memory leaks (see
> /sys/kernel/debug/kmemleak)
>
> I double checked via /proc/slabinfo:
>
> SCTPv6 4373 4420 2368 13 8 : tunables 0 0
> 0 : slabdata 340 340 0
>
> SCTPv6 starts with almost 0, but grows infinitely while I run the
> program in a loop.
>
> Here is my SCTP related configs:
>
> CONFIG_IP_SCTP=y
> CONFIG_NET_SCTPPROBE=y
> CONFIG_SCTP_DBG_OBJCNT=y
> # CONFIG_SCTP_DEFAULT_COOKIE_HMAC_MD5 is not set
> # CONFIG_SCTP_DEFAULT_COOKIE_HMAC_SHA1 is not set
> CONFIG_SCTP_DEFAULT_COOKIE_HMAC_NONE=y
> # CONFIG_SCTP_COOKIE_HMAC_MD5 is not set
> # CONFIG_SCTP_COOKIE_HMAC_SHA1 is not set
>
> I am on commit 67990608c8b95d2b8ccc29932376ae73d5818727 and I don't
> seem to have any sctp-related changes on top.
Ok, now I can. Enabled slub debugs, now I cannot see calls to
sctp_destroy_sock. I see to sctp_close, but not to sctp_destroy_sock.
And SCTPv6 grew by 2 sockets after the execution.
Further checking, it's a race within SCTP asoc migration:
thread 0 thread 1
- app creates a sock
- sends a packet to itself
- sctp will create an asoc and do implicit
handshake
- send the packet
- listen()
- accept() is called and
that asoc is migrated
- packet is delivered
- skb->destructor is called, BUT:
(note that if accept() is called after packet is delivered and skb is freed, it
doesn't happen)
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;
...
atomic_sub(sizeof(struct sctp_chunk), &sk->sk_wmem_alloc);
and it's pointing to the new socket already. So one socket gets a leak
on sk_wmem_alloc and another gets a negative value:
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -1537,12 +1537,14 @@ static void sctp_close(struct sock *sk, long timeout)
/* Hold the sock, since sk_common_release() will put sock_put()
* and we have just a little more cleanup.
*/
+ printk("%s sock_hold %p\n", __func__, sk);
sock_hold(sk);
sk_common_release(sk);
bh_unlock_sock(sk);
spin_unlock_bh(&net->sctp.addr_wq_lock);
+ printk("%s sock_put %p %d %d\n", __func__, sk, atomic_read(&sk->sk_refcnt), atomic_read(&sk->sk_wmem_alloc));
sock_put(sk);
SCTP_DBG_OBJCNT_DEC(sock);
gave me:
[ 99.456944] sctp_close sock_hold ffff880137df8940
...
[ 99.457337] sctp_close sock_put ffff880137df8940 1 -247
[ 99.458313] sctp_close sock_hold ffff880137dfef00
...
[ 99.458383] sctp_close sock_put ffff880137dfef00 1 249
That's why the socket is not freed..
---8<---
As reported by Dmitry, we cannot migrate asocs that have skbs in tx
queue because they have the destructor callback pointing to the asoc,
but which will point to a different socket if we migrate the asoc in
between the packet sent and packet release.
This patch implements proper error handling for sctp_sock_migrate and
this first sanity check.
Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
---
net/sctp/socket.c | 31 ++++++++++++++++++++++++-------
1 file changed, 24 insertions(+), 7 deletions(-)
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 9bb80ec4c08f..5a22a6cfb699 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -99,8 +99,8 @@ static int sctp_send_asconf(struct sctp_association *asoc,
struct sctp_chunk *chunk);
static int sctp_do_bind(struct sock *, union sctp_addr *, int);
static int sctp_autobind(struct sock *sk);
-static void sctp_sock_migrate(struct sock *, struct sock *,
- struct sctp_association *, sctp_socket_type_t);
+static int sctp_sock_migrate(struct sock *, struct sock *,
+ struct sctp_association *, sctp_socket_type_t);
static int sctp_memory_pressure;
static atomic_long_t sctp_memory_allocated;
@@ -3929,7 +3929,11 @@ static struct sock *sctp_accept(struct sock *sk, int flags, int *err)
/* Populate the fields of the newsk from the oldsk and migrate the
* asoc to the newsk.
*/
- sctp_sock_migrate(sk, newsk, asoc, SCTP_SOCKET_TCP);
+ error = sctp_sock_migrate(sk, newsk, asoc, SCTP_SOCKET_TCP);
+ if (error) {
+ sk_common_release(newsk);
+ newsk = NULL;
+ }
out:
release_sock(sk);
@@ -4436,10 +4440,16 @@ int sctp_do_peeloff(struct sock *sk, sctp_assoc_t id, struct socket **sockp)
/* Populate the fields of the newsk from the oldsk and migrate the
* asoc to the newsk.
*/
- sctp_sock_migrate(sk, sock->sk, asoc, SCTP_SOCKET_UDP_HIGH_BANDWIDTH);
+ err = sctp_sock_migrate(sk, sock->sk, asoc,
+ SCTP_SOCKET_UDP_HIGH_BANDWIDTH);
+ if (err) {
+ sk_common_release(sock->sk);
+ goto out;
+ }
*sockp = sock;
+out:
return err;
}
EXPORT_SYMBOL(sctp_do_peeloff);
@@ -7217,9 +7227,9 @@ static inline void sctp_copy_descendant(struct sock *sk_to,
/* Populate the fields of the newsk from the oldsk and migrate the assoc
* and its messages to the newsk.
*/
-static void sctp_sock_migrate(struct sock *oldsk, struct sock *newsk,
- struct sctp_association *assoc,
- sctp_socket_type_t type)
+static int sctp_sock_migrate(struct sock *oldsk, struct sock *newsk,
+ struct sctp_association *assoc,
+ sctp_socket_type_t type)
{
struct sctp_sock *oldsp = sctp_sk(oldsk);
struct sctp_sock *newsp = sctp_sk(newsk);
@@ -7229,6 +7239,12 @@ static void sctp_sock_migrate(struct sock *oldsk, struct sock *newsk,
struct sctp_ulpevent *event;
struct sctp_bind_hashbucket *head;
+ /* We cannot migrate asocs that have skbs tied to it otherwise
+ * its destructor will update the wrong socket
+ */
+ if (assoc->sndbuf_used)
+ return -EBUSY;
+
/* Migrate socket buffer sizes and all the socket level options to the
* new socket.
*/
@@ -7343,6 +7359,8 @@ static void sctp_sock_migrate(struct sock *oldsk, struct sock *newsk,
newsk->sk_state = SCTP_SS_ESTABLISHED;
release_sock(newsk);
+
+ return 0;
}
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