Re: qemu-sockets: account for trailing \0 byte in unix socket pathname

[Michael Tokarev]

31.08.2021 01:54, Michael Tokarev wrote:
> Linux kernel can return size of af_unix socket to be
> one byte larger than sockaddr_un structure - adding
> the trailing zero byte.
>
> Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
> Fixes: 4cfd970ec188558daa6214f26203fe553fb1e01f (first in 6.1.0)
> Cc: qemu-stable@nongnu.org
>
> diff --git a/util/qemu-sockets.c b/util/qemu-sockets.c
> index f2f3676d1f..83926dc2bc 100644
> --- a/util/qemu-sockets.c
> +++ b/util/qemu-sockets.c
> @@ -1345,8 +1345,9 @@ socket_sockaddr_to_address_unix(struct sockaddr_storage 
> *sa,
>       SocketAddress *addr;
>       struct sockaddr_un *su = (struct sockaddr_un *)sa;
>   
> +    /* kernel might have added \0 terminator to non-abstract socket */
>       assert(salen >= sizeof(su->sun_family) + 1 &&
> -           salen <= sizeof(struct sockaddr_un));
> +           salen <= sizeof(struct sockaddr_un) + su->sun_path[0] ? 1 : 0);
>   
>       addr = g_new0(SocketAddress, 1);
>       addr->type = SOCKET_ADDRESS_TYPE_UNIX;

Actually, this is not sufficient.

While this change fixes one issue (the famous trailing null byte \0),
the actual assertion failure occurs because salen = 2, ie, too SMALL,
not too large.

So it looks like libvirt provides an unnamed socket there, --
maybe from a socketpair(2)?

Hwell..

/mjt