Re: [PATCH 19/26] net/ipv6: switch ipv6_flowlabel_opt to sockptr_t

Ido Schimmel
2020-07-27T12:15:05Z

On Thu, Jul 23, 2020 at 08:09:01AM +0200, Christoph Hellwig wrote:
> Pass a sockptr_t to prepare for set_fs-less handling of the kernel
> pointer from bpf-cgroup.
>
> Note that the get case is pretty weird in that it actually copies data
> back to userspace from setsockopt.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> include/net/ipv6.h | 2 +-
> net/ipv6/ip6_flowlabel.c | 16 +++++++++-------
> net/ipv6/ipv6_sockglue.c | 2 +-
> 3 files changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/include/net/ipv6.h b/include/net/ipv6.h
> index 262fc88dbd7e2f..4c9d89b5d73268 100644
> --- a/include/net/ipv6.h
> +++ b/include/net/ipv6.h
> @@ -406,7 +406,7 @@ struct ipv6_txoptions *fl6_merge_options(struct ipv6_txoptions *opt_space,
> struct ip6_flowlabel *fl,
> struct ipv6_txoptions *fopt);
> void fl6_free_socklist(struct sock *sk);
> -int ipv6_flowlabel_opt(struct sock *sk, char __user *optval, int optlen);
> +int ipv6_flowlabel_opt(struct sock *sk, sockptr_t optval, int optlen);
> int ipv6_flowlabel_opt_get(struct sock *sk, struct in6_flowlabel_req *freq,
> int flags);
> int ip6_flowlabel_init(void);
> diff --git a/net/ipv6/ip6_flowlabel.c b/net/ipv6/ip6_flowlabel.c
> index 27ee6de9beffc4..6b3c315f3d461a 100644
> --- a/net/ipv6/ip6_flowlabel.c
> +++ b/net/ipv6/ip6_flowlabel.c
> @@ -371,7 +371,7 @@ static int fl6_renew(struct ip6_flowlabel *fl, unsigned long linger, unsigned lo
>
> static struct ip6_flowlabel *
> fl_create(struct net *net, struct sock *sk, struct in6_flowlabel_req *freq,
> - char __user *optval, int optlen, int *err_p)
> + sockptr_t optval, int optlen, int *err_p)
> {
> struct ip6_flowlabel *fl = NULL;
> int olen;
> @@ -401,7 +401,8 @@ fl_create(struct net *net, struct sock *sk, struct in6_flowlabel_req *freq,
> memset(fl->opt, 0, sizeof(*fl->opt));
> fl->opt->tot_len = sizeof(*fl->opt) + olen;
> err = -EFAULT;
> - if (copy_from_user(fl->opt+1, optval+CMSG_ALIGN(sizeof(*freq)), olen))
> + sockptr_advance(optval, CMSG_ALIGN(sizeof(*freq)));
> + if (copy_from_sockptr(fl->opt + 1, optval, olen))
> goto done;
>
> msg.msg_controllen = olen;
> @@ -604,7 +605,7 @@ static int ipv6_flowlabel_renew(struct sock *sk, struct in6_flowlabel_req *freq)
> }
>
> static int ipv6_flowlabel_get(struct sock *sk, struct in6_flowlabel_req *freq,
> - void __user *optval, int optlen)
> + sockptr_t optval, int optlen)
> {
> struct ipv6_fl_socklist *sfl, *sfl1 = NULL;
> struct ip6_flowlabel *fl, *fl1 = NULL;
> @@ -702,8 +703,9 @@ static int ipv6_flowlabel_get(struct sock *sk, struct in6_flowlabel_req *freq,
> goto recheck;
>
> if (!freq->flr_label) {
> - if (copy_to_user(&((struct in6_flowlabel_req __user *) optval)->flr_label,
> - &fl->label, sizeof(fl->label))) {
> + sockptr_advance(optval,
> + offsetof(struct in6_flowlabel_req, flr_label));

Christoph,

I see a regression with IPv6 flowlabel that I bisected to this patch.
When passing '-F 0' to 'ping' the flow label should be random, yet it's
the same every time after this patch.

It seems that the pointer is never advanced after the call to
sockptr_advance() because it is passed by value and not by reference.
Even if you were to pass it by reference I think you would later need to
call sockptr_decrease() or something similar. Otherwise it is very
error-prone.

Maybe adding an offset to copy_to_sockptr() and copy_from_sockptr() is
better?

Thanks

> + if (copy_to_sockptr(optval, &fl->label, sizeof(fl->label))) {
> /* Intentionally ignore fault. */
> }
> }
> @@ -716,13 +718,13 @@ static int ipv6_flowlabel_get(struct sock *sk, struct in6_flowlabel_req *freq,
> return err;
> }
>
> -int ipv6_flowlabel_opt(struct sock *sk, char __user *optval, int optlen)
> +int ipv6_flowlabel_opt(struct sock *sk, sockptr_t optval, int optlen)
> {
> struct in6_flowlabel_req freq;
>
> if (optlen < sizeof(freq))
> return -EINVAL;
> - if (copy_from_user(&freq, optval, sizeof(freq)))
> + if (copy_from_sockptr(&freq, optval, sizeof(freq)))
> return -EFAULT;
>
> switch (freq.flr_action) {
> diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
> index 119dfaf5f4bb26..3897fb55372d38 100644
> --- a/net/ipv6/ipv6_sockglue.c
> +++ b/net/ipv6/ipv6_sockglue.c
> @@ -929,7 +929,7 @@ static int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
> retv = 0;
> break;
> case IPV6_FLOWLABEL_MGR:
> - retv = ipv6_flowlabel_opt(sk, optval, optlen);
> + retv = ipv6_flowlabel_opt(sk, USER_SOCKPTR(optval), optlen);
> break;
> case IPV6_IPSEC_POLICY:
> case IPV6_XFRM_POLICY:
> --
> 2.27.0
>