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authorJames Chapman <jchapman@katalix.com>2018-02-23 20:45:46 +0300
committerDavid S. Miller <davem@davemloft.net>2018-02-26 20:20:36 +0300
commitd02ba2a6110c530a32926af8ad441111774d2893 (patch)
tree547933c64536511f4e86212fe8a485f270048ab3 /net/l2tp
parentd00fa9adc528c1b0e64d532556764852df8bd7b9 (diff)
downloadlinux-d02ba2a6110c530a32926af8ad441111774d2893.tar.xz
l2tp: fix race in pppol2tp_release with session object destroy
pppol2tp_release uses call_rcu to put the final ref on its socket. But the session object doesn't hold a ref on the session socket so may be freed while the pppol2tp_put_sk RCU callback is scheduled. Fix this by having the session hold a ref on its socket until the session is destroyed. It is this ref that is dropped via call_rcu. Sessions are also deleted via l2tp_tunnel_closeall. This must now also put the final ref via call_rcu. So move the call_rcu call site into pppol2tp_session_close so that this happens in both destroy paths. A common destroy path should really be implemented, perhaps with l2tp_tunnel_closeall calling l2tp_session_delete like pppol2tp_release does, but this will be looked at later. ODEBUG: activate active (active state 1) object type: rcu_head hint: (null) WARNING: CPU: 3 PID: 13407 at lib/debugobjects.c:291 debug_print_object+0x166/0x220 Modules linked in: CPU: 3 PID: 13407 Comm: syzbot_19c09769 Not tainted 4.16.0-rc2+ #38 Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006 RIP: 0010:debug_print_object+0x166/0x220 RSP: 0018:ffff880013647a00 EFLAGS: 00010082 RAX: dffffc0000000008 RBX: 0000000000000003 RCX: ffffffff814d3333 RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff88001a59f6d0 RBP: ffff880013647a40 R08: 0000000000000000 R09: 0000000000000001 R10: ffff8800136479a8 R11: 0000000000000000 R12: 0000000000000001 R13: ffffffff86161420 R14: ffffffff85648b60 R15: 0000000000000000 FS: 0000000000000000(0000) GS:ffff88001a580000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000020e77000 CR3: 0000000006022000 CR4: 00000000000006e0 Call Trace: debug_object_activate+0x38b/0x530 ? debug_object_assert_init+0x3b0/0x3b0 ? __mutex_unlock_slowpath+0x85/0x8b0 ? pppol2tp_session_destruct+0x110/0x110 __call_rcu.constprop.66+0x39/0x890 ? __call_rcu.constprop.66+0x39/0x890 call_rcu_sched+0x17/0x20 pppol2tp_release+0x2c7/0x440 ? fcntl_setlk+0xca0/0xca0 ? sock_alloc_file+0x340/0x340 sock_release+0x92/0x1e0 sock_close+0x1b/0x20 __fput+0x296/0x6e0 ____fput+0x1a/0x20 task_work_run+0x127/0x1a0 do_exit+0x7f9/0x2ce0 ? SYSC_connect+0x212/0x310 ? mm_update_next_owner+0x690/0x690 ? up_read+0x1f/0x40 ? __do_page_fault+0x3c8/0xca0 do_group_exit+0x10d/0x330 ? do_group_exit+0x330/0x330 SyS_exit_group+0x22/0x30 do_syscall_64+0x1e0/0x730 ? trace_hardirqs_off_thunk+0x1a/0x1c entry_SYSCALL_64_after_hwframe+0x42/0xb7 RIP: 0033:0x7f362e471259 RSP: 002b:00007ffe389abe08 EFLAGS: 00000202 ORIG_RAX: 00000000000000e7 RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f362e471259 RDX: 00007f362e471259 RSI: 000000000000002e RDI: 0000000000000000 RBP: 00007ffe389abe30 R08: 0000000000000000 R09: 00007f362e944270 R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000400b60 R13: 00007ffe389abf50 R14: 0000000000000000 R15: 0000000000000000 Code: 8d 3c dd a0 8f 64 85 48 89 fa 48 c1 ea 03 80 3c 02 00 75 7b 48 8b 14 dd a0 8f 64 85 4c 89 f6 48 c7 c7 20 85 64 85 e 8 2a 55 14 ff <0f> 0b 83 05 ad 2a 68 04 01 48 83 c4 18 5b 41 5c 41 5d 41 5e 41 Fixes: ee40fb2e1eb5b ("l2tp: protect sock pointer of struct pppol2tp_session with RCU") Signed-off-by: James Chapman <jchapman@katalix.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/l2tp')
-rw-r--r--net/l2tp/l2tp_ppp.c52
1 files changed, 27 insertions, 25 deletions
diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index 2d2955e8f710..3b02f24ea9ec 100644
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -416,10 +416,28 @@ abort:
* Session (and tunnel control) socket create/destroy.
*****************************************************************************/
+static void pppol2tp_put_sk(struct rcu_head *head)
+{
+ struct pppol2tp_session *ps;
+
+ ps = container_of(head, typeof(*ps), rcu);
+ sock_put(ps->__sk);
+}
+
/* Called by l2tp_core when a session socket is being closed.
*/
static void pppol2tp_session_close(struct l2tp_session *session)
{
+ struct pppol2tp_session *ps;
+
+ ps = l2tp_session_priv(session);
+ mutex_lock(&ps->sk_lock);
+ ps->__sk = rcu_dereference_protected(ps->sk,
+ lockdep_is_held(&ps->sk_lock));
+ RCU_INIT_POINTER(ps->sk, NULL);
+ if (ps->__sk)
+ call_rcu(&ps->rcu, pppol2tp_put_sk);
+ mutex_unlock(&ps->sk_lock);
}
/* Really kill the session socket. (Called from sock_put() if
@@ -439,14 +457,6 @@ static void pppol2tp_session_destruct(struct sock *sk)
}
}
-static void pppol2tp_put_sk(struct rcu_head *head)
-{
- struct pppol2tp_session *ps;
-
- ps = container_of(head, typeof(*ps), rcu);
- sock_put(ps->__sk);
-}
-
/* Called when the PPPoX socket (session) is closed.
*/
static int pppol2tp_release(struct socket *sock)
@@ -470,26 +480,17 @@ static int pppol2tp_release(struct socket *sock)
sock_orphan(sk);
sock->sk = NULL;
+ /* If the socket is associated with a session,
+ * l2tp_session_delete will call pppol2tp_session_close which
+ * will drop the session's ref on the socket.
+ */
session = pppol2tp_sock_to_session(sk);
-
- if (session != NULL) {
- struct pppol2tp_session *ps;
-
+ if (session) {
l2tp_session_delete(session);
-
- ps = l2tp_session_priv(session);
- mutex_lock(&ps->sk_lock);
- ps->__sk = rcu_dereference_protected(ps->sk,
- lockdep_is_held(&ps->sk_lock));
- RCU_INIT_POINTER(ps->sk, NULL);
- mutex_unlock(&ps->sk_lock);
- call_rcu(&ps->rcu, pppol2tp_put_sk);
-
- /* Rely on the sock_put() call at the end of the function for
- * dropping the reference held by pppol2tp_sock_to_session().
- * The last reference will be dropped by pppol2tp_put_sk().
- */
+ /* drop the ref obtained by pppol2tp_sock_to_session */
+ sock_put(sk);
}
+
release_sock(sk);
/* This will delete the session context via
@@ -786,6 +787,7 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
out_no_ppp:
/* This is how we get the session context from the socket. */
+ sock_hold(sk);
sk->sk_user_data = session;
rcu_assign_pointer(ps->sk, sk);
mutex_unlock(&ps->sk_lock);