Re: [PATCH 5/5] net: Block MSG_CMSG_COMPAT in send(m)msg and recv(m)msg

[Michael Neuling]

On Thu, May 23, 2013 at 7:07 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> MSG_CMSG_COMPAT is (AFAIK) not intended to be part of the API --
> it's a hack that steals a bit to indicate to other networking code
> that a compat entry was used.  So don't allow it from a non-compat
> syscall.

Dave & Linus

This is causing a regression on 64bit powerpc with 32bit usermode.
When I hit userspace, udev is broken and I suspect all networking is
broken as well.

Can we please revert 1be374a0518a288147c6a7398792583200a67261 upstream?

Found via bisect.

Mikey

>
> This prevents an oops when running this code:
>
> int main()
> {
>         int s;
>         struct sockaddr_in addr;
>         struct msghdr *hdr;
>
>         char *highpage = mmap((void*)(TASK_SIZE_MAX - 4096), 4096,
>                               PROT_READ | PROT_WRITE,
>                               MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
>         if (highpage == MAP_FAILED)
>                 err(1, "mmap");
>
>         s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
>         if (s == -1)
>                 err(1, "socket");
>
>         addr.sin_family = AF_INET;
>         addr.sin_port = htons(1);
>         addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);This is upster

>         if (connect(s, (struct sockaddr*)&addr, sizeof(addr)) != 0)
>                 err(1, "connect");
>
>         void *evil = highpage + 4096 - COMPAT_MSGHDR_SIZE;
>         printf("Evil address is %p\n", evil);
>
>         if (syscall(__NR_sendmmsg, s, evil, 1, MSG_CMSG_COMPAT) < 0)
>                 err(1, "sendmmsg");
>
>         return 0;
> }
>
> Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> ---
>  net/socket.c | 33 +++++++++++++++++++++++++++++++--
>  1 file changed, 31 insertions(+), 2 deletions(-)
>
> diff --git a/net/socket.c b/net/socket.c
> index 88f759a..0e16888 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -2097,8 +2097,12 @@ SYSCALL_DEFINE3(sendmsg, int, fd, struct msghdr __user *, msg, unsigned int, fla
>  {
>         int fput_needed, err;
>         struct msghdr msg_sys;
> -       struct socket *sock = sockfd_lookup_light(fd, &err, &fput_needed);
> +       struct socket *sock;
> +
> +       if (flags & MSG_CMSG_COMPAT)
> +               return -EINVAL;
>
> +       sock = sockfd_lookup_light(fd, &err, &fput_needed);
>         if (!sock)
>                 goto out;
>
> @@ -2171,6 +2175,8 @@ int __sys_sendmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
>  SYSCALL_DEFINE4(sendmmsg, int, fd, struct mmsghdr __user *, mmsg,
>                 unsigned int, vlen, unsigned int, flags)
>  {
> +       if (flags & MSG_CMSG_COMPAT)
> +               return -EINVAL;
>         return __sys_sendmmsg(fd, mmsg, vlen, flags);
>  }
>
> @@ -2271,8 +2277,12 @@ SYSCALL_DEFINE3(recvmsg, int, fd, struct msghdr __user *, msg,
>  {
>         int fput_needed, err;
>         struct msghdr msg_sys;
> -       struct socket *sock = sockfd_lookup_light(fd, &err, &fput_needed);
> +       struct socket *sock;
> +
> +       if (flags & MSG_CMSG_COMPAT)
> +               return -EINVAL;
>
> +       sock = sockfd_lookup_light(fd, &err, &fput_needed);
>         if (!sock)
>                 goto out;
>
> @@ -2397,6 +2407,9 @@ SYSCALL_DEFINE5(recvmmsg, int, fd, struct mmsghdr __user *, mmsg,
>         int datagrams;
>         struct timespec timeout_sys;
>
> +       if (flags & MSG_CMSG_COMPAT)
> +               return -EINVAL;
> +
>         if (!timeout)
>                 return __sys_recvmmsg(fd, mmsg, vlen, flags, NULL);
>
> @@ -2512,15 +2525,31 @@ SYSCALL_DEFINE2(socketcall, int, call, unsigned long __user *, args)
>                                    (int __user *)a[4]);
>                 break;
>         case SYS_SENDMSG:
> +               if (a[2] & MSG_CMSG_COMPAT) {
> +                       err = -EINVAL;
> +                       break;
> +               }
>                 err = sys_sendmsg(a0, (struct msghdr __user *)a1, a[2]);
>                 break;
>         case SYS_SENDMMSG:
> +               if (a[3] & MSG_CMSG_COMPAT) {
> +                       err = -EINVAL;
> +                       break;
> +               }
>                 err = sys_sendmmsg(a0, (struct mmsghdr __user *)a1, a[2], a[3]);
>                 break;
>         case SYS_RECVMSG:
> +               if (a[2] & MSG_CMSG_COMPAT) {
> +                       err = -EINVAL;
> +                       break;
> +               }
>                 err = sys_recvmsg(a0, (struct msghdr __user *)a1, a[2]);
>                 break;
>         case SYS_RECVMMSG:
> +               if (a[3] & MSG_CMSG_COMPAT) {
> +                       err = -EINVAL;
> +                       break;
> +               }
>                 err = sys_recvmmsg(a0, (struct mmsghdr __user *)a1, a[2], a[3],
>                                    (struct timespec __user *)a[4]);
>                 break;
> --
> 1.8.1.4
>
> --
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