Re: [Qemu-devel] [PATCH 0/2] linux-user: Fix length handling in cmsg conversions

[Peter Maydell]

Ping?

thanks
-- PMM

On 26 May 2015 at 19:46, Peter Maydell <address@hidden> wrote:
> This patchset fixes some problems in conversions of cmsg structures
> in target_to_host_cmsg() (used in send/recvmsg handling). Specifically:
>
>      * we required the msg->msg_controllen to declare the buffer
>        to have enough space for final trailing padding (we were
>        checking against CMSG_SPACE), whereas the kernel does not
>        require this, and common userspace code assumes this.
>      * we weren't correctly handling the fact that the SO_TIMESTAMP
>        payload may be larger for the target than the host
>      * we weren't marking the messages with MSG_CTRUNC when we did
>        need to truncate a message that wasn't truncated by the host,
>        but were instead logging a QEMU message; since truncation is
>        always the result of a guest giving us an insufficiently
>        sized buffer, we should report it to the guest as the kernel
>        does and don't log anything
>      * we weren't handling the possibility of the host having a
>        more restrictive alignment requirement for payload structs
>
> The major visible issue I wanted to fix is that glibc's "try to talk
> to nscd" code that it will run on startup will receive a cmsg with a
> 4 byte payload and only allocates 4 bytes for it, which was causing
> us to do the wrong thing on architectures that need 8-alignment
> (we dropped the cmsg and printed a diagnostic message).
>
>
> Peter Maydell (2):
>   linux-user: Fix length handling in host_to_target_cmsg
>   linux-user: use __get_user and __put_user in cmsg conversions
>
>  linux-user/syscall.c | 89 
> ++++++++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 72 insertions(+), 17 deletions(-)
>
> --
> 1.9.1