Re: [Qemu-devel] [PATCH] sockets: report error if UNIX socket path is too long

[Eric Blake <eblake@redhat.com>]

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On 05/24/2017 10:42 AM, Daniel P. Berrange wrote:
> The 'struct sockaddr_un' only allows 108 bytes for the socket
> path. Currently QEMU uses snprintf() and so silently truncates
> the socket path provided by the user. This is undesirable because
> the user will then be unable to connect to the path they asked
> for. This change makes QEMU bounds check and report an explicit
> error message.
> 
> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
> ---
>  util/qemu-sockets.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/util/qemu-sockets.c b/util/qemu-sockets.c
> index d8183f7..e249dbe 100644
> --- a/util/qemu-sockets.c
> +++ b/util/qemu-sockets.c
> @@ -855,6 +855,12 @@ static int unix_listen_saddr(UnixSocketAddress *saddr,
>      memset(&un, 0, sizeof(un));
>      un.sun_family = AF_UNIX;
>      if (saddr->path && strlen(saddr->path)) {
> +        if (strlen(saddr->path) > sizeof(un.sun_path)) {

Feels odd to be computing strlen(saddr->path) multiple times instead of
storing it in a temporary.

> +            error_setg(errp, "UNIX socket path '%s' is too long", saddr->path);
> +            error_append_hint(errp, "Path must be less than %zu bytes\n",
> +                              sizeof(un.sun_path));
> +            return -1;
> +        }
>          snprintf(un.sun_path, sizeof(un.sun_path), "%s", saddr->path);

Pre-existing, but now that we know things fit, isn't it faster to use
strcpy (or strpcpy or strncpy) instead of the overhead of snprintf?

You're on the right track, but it may be worth a v2 for further cleanups.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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