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 @@ -1391,7 +1391,14 @@ 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;