[PATCH 5.15 080/244] vsock: Fix memory leak in vsock_connect()

Greg Kroah-Hartman
2022-08-23T09:58:06Z

From: Peilin Ye <peilin.ye@bytedance.com>

commit 7e97cfed9929eaabc41829c395eb0d1350fccb9d upstream.

An O_NONBLOCK vsock_connect() request may try to reschedule
@connect_work. Imagine the following sequence of vsock_connect()
requests:

1. The 1st, non-blocking request schedules @connect_work, which will
expire after 200 jiffies. Socket state is now SS_CONNECTING;

2. Later, the 2nd, blocking request gets interrupted by a signal after
a few jiffies while waiting for the connection to be established.
Socket state is back to SS_UNCONNECTED, but @connect_work is still
pending, and will expire after 100 jiffies.

3. Now, the 3rd, non-blocking request tries to schedule @connect_work
again. Since @connect_work is already scheduled,
schedule_delayed_work() silently returns. sock_hold() is called
twice, but sock_put() will only be called once in
vsock_connect_timeout(), causing a memory leak reported by syzbot:

BUG: memory leak
unreferenced object 0xffff88810ea56a40 (size 1232):
comm "syz-executor756", pid 3604, jiffies 4294947681 (age 12.350s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
28 00 07 40 00 00 00 00 00 00 00 00 00 00 00 00 (..@............
backtrace:
[<ffffffff837c830e>] sk_prot_alloc+0x3e/0x1b0 net/core/sock.c:1930
[<ffffffff837cbe22>] sk_alloc+0x32/0x2e0 net/core/sock.c:1989
[<ffffffff842ccf68>] __vsock_create.constprop.0+0x38/0x320 net/vmw_vsock/af_vsock.c:734
[<ffffffff842ce8f1>] vsock_create+0xc1/0x2d0 net/vmw_vsock/af_vsock.c:2203
[<ffffffff837c0cbb>] __sock_create+0x1ab/0x2b0 net/socket.c:1468
[<ffffffff837c3acf>] sock_create net/socket.c:1519 [inline]
[<ffffffff837c3acf>] __sys_socket+0x6f/0x140 net/socket.c:1561
[<ffffffff837c3bba>] __do_sys_socket net/socket.c:1570 [inline]
[<ffffffff837c3bba>] __se_sys_socket net/socket.c:1568 [inline]
[<ffffffff837c3bba>] __x64_sys_socket+0x1a/0x20 net/socket.c:1568
[<ffffffff84512815>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
[<ffffffff84512815>] do_syscall_64+0x35/0x80 arch/x86/entry/common.c:80
[<ffffffff84600068>] entry_SYSCALL_64_after_hwframe+0x44/0xae
<...>

Use mod_delayed_work() instead: if @connect_work is already scheduled,
reschedule it, and undo sock_hold() to keep the reference count
balanced.

Reported-and-tested-by: syzbot+b03f55bf128f9a38f064@syzkaller.appspotmail.com
Fixes: d021c344051a ("VSOCK: Introduce VM Sockets")
Co-developed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/vmw_vsock/af_vsock.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -1390,7 +1390,14 @@ static int vsock_connect(struct socket *
* timeout fires.
*/
sock_hold(sk);
- schedule_delayed_work(&vsk->connect_work, timeout);
+
+ /* If the timeout function is already scheduled,
+ * reschedule it, then ungrab the socket refcount to
+ * keep it balanced.
+ */
+ if (mod_delayed_work(system_wq, &vsk->connect_work,
+ timeout))
+ sock_put(sk);

/* Skip ahead to preserve error code set above. */
goto out_wait;