[Qemu-devel] [Bug 1643619] [NEW] netlink broken on big-endian mips

[James Cowgill <jcowgill@debian.org>]

Public bug reported:

Debian QEMU version 2.7.0, but the bug also appears in current git
master (commit c36ed06e9159)

As the summary says, netlink is completely broken on big-endian mips
running qemu-user.

Running 'ip route' from within a Debian chroot with QEMU simply hangs.
Running amd64 strace on qemu-mips-static shows that it's waiting for a
netlink response from the kernel which never comes.

[...]
[pid 11249] socket(AF_NETLINK, SOCK_RAW|SOCK_CLOEXEC, NETLINK_ROUTE) = 3
[pid 11249] setsockopt(3, SOL_SOCKET, SO_SNDBUF, [32768], 4) = 0
[pid 11249] setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
[pid 11249] bind(3, {sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, 12) = 0
[pid 11249] getsockname(3, {sa_family=AF_NETLINK, nl_pid=11249, nl_groups=00000000}, [12]) = 0
[pid 11249] time([1479745823])          = 1479745823
[pid 11249] sendto(3, {{len=671088640, type=0x1a00 /* NLMSG_??? */, flags=NLM_F_REQUEST|NLM_F_MULTI|0x100, seq=539046744, pid=0}, "\2\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\10\0\35\0\0\0\1"}, 40, 0, NULL, 0) = 40
[pid 11249] recvmsg(3,

Notice the len in the buffer passed to the kernel is 0x28000000 which
looks byteswapped.

Removing the call to fd_trans_unregister in the NR_socket syscall in
do_syscall fixes this for me, but I don't understand why the fd
translation was immediately unregistered after being registered just
before in do_socket - presumably it was added for a reason.

--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -9331,7 +9331,6 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
 #ifdef TARGET_NR_socket
     case TARGET_NR_socket:
         ret = do_socket(arg1, arg2, arg3);
-        fd_trans_unregister(ret);
         break;
 #endif
 #ifdef TARGET_NR_socketpair

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1643619

Title:
  netlink broken on big-endian mips

Status in QEMU:
  New

Bug description:
  Debian QEMU version 2.7.0, but the bug also appears in current git
  master (commit c36ed06e9159)

  As the summary says, netlink is completely broken on big-endian mips
  running qemu-user.

  Running 'ip route' from within a Debian chroot with QEMU simply hangs.
  Running amd64 strace on qemu-mips-static shows that it's waiting for a
  netlink response from the kernel which never comes.

  [...]
  [pid 11249] socket(AF_NETLINK, SOCK_RAW|SOCK_CLOEXEC, NETLINK_ROUTE) = 3
  [pid 11249] setsockopt(3, SOL_SOCKET, SO_SNDBUF, [32768], 4) = 0
  [pid 11249] setsockopt(3, SOL_SOCKET, SO_RCVBUF, [1048576], 4) = 0
  [pid 11249] bind(3, {sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, 12) = 0
  [pid 11249] getsockname(3, {sa_family=AF_NETLINK, nl_pid=11249, nl_groups=00000000}, [12]) = 0
  [pid 11249] time([1479745823])          = 1479745823
  [pid 11249] sendto(3, {{len=671088640, type=0x1a00 /* NLMSG_??? */, flags=NLM_F_REQUEST|NLM_F_MULTI|0x100, seq=539046744, pid=0}, "\2\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\10\0\35\0\0\0\1"}, 40, 0, NULL, 0) = 40
  [pid 11249] recvmsg(3,

  Notice the len in the buffer passed to the kernel is 0x28000000 which
  looks byteswapped.

  Removing the call to fd_trans_unregister in the NR_socket syscall in
  do_syscall fixes this for me, but I don't understand why the fd
  translation was immediately unregistered after being registered just
  before in do_socket - presumably it was added for a reason.

  --- a/linux-user/syscall.c
  +++ b/linux-user/syscall.c
  @@ -9331,7 +9331,6 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
   #ifdef TARGET_NR_socket
       case TARGET_NR_socket:
           ret = do_socket(arg1, arg2, arg3);
  -        fd_trans_unregister(ret);
           break;
   #endif
   #ifdef TARGET_NR_socketpair

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