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Re: [Qemu-devel] [PATCH] net: avoid to use variable length array in net_
From: |
Stefano Garzarella |
Subject: |
Re: [Qemu-devel] [PATCH] net: avoid to use variable length array in net_client_init() |
Date: |
Mon, 6 May 2019 19:42:22 +0200 |
User-agent: |
NeoMutt/20180716 |
On Mon, May 06, 2019 at 03:23:08PM +0200, Markus Armbruster wrote:
> Stefano Garzarella <address@hidden> writes:
>
> > net_client_init() uses a variable length array to store the prefix
> > of 'ipv6-net' parameter (e.g. if ipv6-net=fec0::0/64, the prefix
> > is 'fec0::0').
> > Since the IPv6 prefix can be at most as long as an IPv6 address,
> > we can use an array with fixed size equals to INET6_ADDRSTRLEN.
> >
> > Signed-off-by: Stefano Garzarella <address@hidden>
> > ---
> > net/net.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/net.c b/net/net.c
> > index f3a3c5444c..2e5f27e121 100644
> > --- a/net/net.c
> > +++ b/net/net.c
> > @@ -1118,7 +1118,7 @@ static int net_client_init(QemuOpts *opts, bool
> > is_netdev, Error **errp)
> > const char *ip6_net = qemu_opt_get(opts, "ipv6-net");
> >
> > if (ip6_net) {
> > - char buf[strlen(ip6_net) + 1];
> > + char buf[INET6_ADDRSTRLEN];
> >
> > if (get_str_sep(buf, sizeof(buf), &ip6_net, '/') < 0) {
> > /* Default 64bit prefix length. */
>
> Hmm.
>
> Parameter "ipv6-net" is of the form ADDRESS[/PREFIX-SIZE]. If
> /PREFIX-SIZE is present, get_str_sep() copies the ADDRESS part to buf[].
>
> However, nothing stops the user from passing in an ADDRESS longer than
> INET6_ADDRSTRLEN, say by adding a enough leading zeros. get_str_sep()
> will then silently truncate ADDRESS.
>
> Suggest to avoid get_str_sep() like this (not even compile-tested):
>
> if (ip6_net) {
> char *slashp = strchr(ip6_net, '/');
>
> if (!slashp) {
> /* Default 64bit prefix length. */
> qemu_opt_set(opts, "ipv6-prefix", ip6_net, &error_abort);
> qemu_opt_set_number(opts, "ipv6-prefixlen", 64, &error_abort);
> } else {
> /* User-specified prefix length. */
> unsigned long len;
> int err;
> char *addr = g_strndup(ip6_net, slashp - ip6_net);
>
> qemu_opt_set(opts, "ipv6-prefix", addr, &error_abort);
> g_free(addr);
> err = qemu_strtoul(slashp + 1, NULL, 10, &len);
> if (err) {
> error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
> "ipv6-prefix", "a number");
> } else {
> qemu_opt_set_number(opts, "ipv6-prefixlen", len,
> &error_abort);
> }
> }
> qemu_opt_unset(opts, "ipv6-net");
> }
> }
Thank you for the suggestion! It seems much better to me.
I'll follow your idea for the v2.
>
> I'd be tempted to clean up further; de-duplicate the qemu_opt_set() and
> qemu_opt_set_number().
Yes, it seems simple to de-duplicate in this way:
if (ip6_net) {
char *slashp = strchr(ip6_net, '/');
char *addr = ip6_net;
unsigned long len = 64;
if (slashp) {
...
}
qemu_opt_set(opts, "ipv6-prefix", addr, &error_abort);
qemu_opt_set_number(opts, "ipv6-prefixlen", len, &error_abort);
qemu_opt_unset(opts, "ipv6-net");
}
>
> There's just one more use of get_str_sep(), in parse_host_port(), and it
> looks just as prone to silent truncation.
I'll check it.
Thanks,
Stefano