Re: [PATCH 03/16 net-next v2] net: inet: relocate ip_generic_getfrag and guard IPv4 socket logic

[netdev-bot+sashiko]

Thank you for your contribution! Sashiko AI review found 5 potential
issue(s) to consider.

Critical: 1 · High: 0 · Medium: 2 · Low: 2

If you believe none of the issues are legitimate, please reply to each
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If any of them are legitimate and you plan to respin, please let patchwork
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- [Critical] Remote NULL-pointer dereference when IPv4 is disabled.
- [Medium] The IPv4 offload ops table is left half-disabled when IPv4 is
  off.
- [Medium] With IPv4 disabled, inet_ioctl() returns -EOPNOTSUPP for every
  command before its switch (net/ipv4/af_inet.c:997-998).
- [Low] The commit message is incomplete and has a typo.
- [Low] (Baseline decision: false — fixed later in the series.) The
  commit message says the same guard rejects IPv4-mapped IPv6, but the…

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net: inet: relocate ip_generic_getfrag and guard IPv4 socket logic

This patch moves ip_generic_getfrag() from ip_output.c to af_inet.c so it
is available without IPv4. It adds CONFIG_IPV4 guards in af_inet.c around
the ioctl, bind, protocol registration, GSO and init paths. It also
rejects IPv4 and v4-mapped addresses in the IPv6 bind and datagram
connect paths.

> This patch moves the generic ip_generec_getfrag() from ip_output.c to
> af_inet.c. It also introduces CONFIG_IPV4 guards around af_inet.c to
> reject IPv4-specific ioctls, protocol registrations and bind requests.

[Severity: Low]
This isn't a bug, but there's a typo: ip_generec_getfrag() should be
ip_generic_getfrag().

The description also leaves out some behavioural changes in the diff:

  - inet_init() now calls init_inet_pernet_ops() before ip_mr_init().
    This changes the pernet init order even with CONFIG_IPV4=y.
  - inet_gso_segment() is disabled when CONFIG_IPV4 is off. That is a
    packet path change, not socket logic.
  - inet_release() skips ip_mc_drop_socket().
  - inet_sk_reselect_saddr() returns early.

Could the commit message mention these as well?

> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index d9421ac38d78c..cf00386933d67 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c

[ ... ]

> @@ -968,6 +994,9 @@ int inet_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
>  	struct ifreq ifr;
>  	struct rtentry rt;
>
> +	if (!IS_ENABLED(CONFIG_IPV4))
> +		return -EOPNOTSUPP;
> +
>  	switch (cmd) {
>  	case SIOCADDRT:
>  	case SIOCDELRT:

[Severity: Medium]
Does this break SIOCSIFFLAGS on AF_PACKET sockets when CONFIG_IPV4 is
disabled?

Under CONFIG_INET, packet_ioctl() still forwards SIOCSIFFLAGS and the
IPv4 address ioctls to inet_dgram_ops.ioctl:

net/packet/af_packet.c:packet_ioctl() {
    ...
	case SIOCSIFFLAGS:
		return inet_dgram_ops.ioctl(sock, cmd, arg);
#endif
    ...
}

sock_do_ioctl() only falls back to dev_ioctl() when ops->ioctl returns
-ENOIOCTLCMD:

net/socket.c:sock_do_ioctl() {
    ...
	err = ops->ioctl(sock, cmd, arg);
    ...
	if (err != -ENOIOCTLCMD)
		return err;
    ...
}

With IPV4=n, sock_do_ioctl()->packet_ioctl()->inet_ioctl() returns
-EOPNOTSUPP. As a result, the call never reaches the
dev_ioctl()->dev_ifsioc() path. That path handles SIOCSIFFLAGS through
dev_change_flags() and does nothing IPv4-specific. With IPV4=y the same
ioctl worked through devinet_ioctl()->dev_change_flags().

Would returning -ENOIOCTLCMD here, at least for commands that aren't
IPv4-specific, keep the generic fallback? This code is unchanged at the
end of the series.

[ ... ]

> @@ -1371,6 +1408,9 @@ struct sk_buff *inet_gso_segment(struct sk_buff *skb,
>  	int ihl;
>  	int id;
>
> +	if (!IS_ENABLED(CONFIG_IPV4))
> +		return ERR_PTR(-EPROTONOSUPPORT);
> +
>  	skb_reset_network_header(skb);
>  	nhoff = skb_network_header(skb) - skb_mac_header(skb);
>  	if (unlikely(!pskb_may_pull(skb, sizeof(*iph))))

[Severity: Medium]
Does this leave the IPv4 offload half disabled?

ipv4_offload_init() has no guard. It still registers the TCPv4, UDPv4
and IPIP offloads, and it registers the IPv4 packet offload with the GRO
callbacks:

	net_hotdata.ip_packet_offload = (struct packet_offload) {
		.type = cpu_to_be16(ETH_P_IP),
		.callbacks = {
			.gso_segment = inet_gso_segment,
			.gro_receive = inet_gro_receive,
			.gro_complete = inet_gro_complete,
		},
	};

Consider an IPV4=n kernel that forwards IPv4 frames at L2 (bridge, OVS,
tc redirect). GRO can still merge IPv4 TCP segments into SKB_GSO_TCPV4
packets.

If the egress device lacks TSO, the chain is:

validate_xmit_skb()
  skb_gso_segment()
    inet_gso_segment()
      return ERR_PTR(-EPROTONOSUPPORT)

The whole aggregate is then freed through out_kfree_skb.
ip4ip6_gso_segment() in net/ipv6/ip6_offload.c also calls
inet_gso_segment() and would fail the same way.

The guard appears to be needed only because inet_gso_segment() calls
ip_send_check(), which is in the IPv4-only ip_output.c.

Could ip_send_check() move to generic code, the same way this patch moves
ip_generic_getfrag()? Or could the IPv4 GRO callbacks stay unregistered
when IPv4 is disabled? This code is unchanged at the end of the series.

[ ... ]

> @@ -1870,20 +1912,25 @@ static int __init ipv4_offload_init(void)

[ ... ]

>  static int __init inet_init(void)
>  {
> +#if IS_ENABLED(CONFIG_IPV4)
>  	struct inet_protosw *q;
>  	struct list_head *r;
>  	int rc;
> +#endif
>
>  	sock_skb_cb_check_size(sizeof(struct inet_skb_parm));
>
> +#if IS_ENABLED(CONFIG_IPV4)
>  	raw_hashinfo_init(&raw_v4_hashinfo);
>
>  	rc = proto_register(&tcp_prot, 1);
> @@ -1958,7 +2005,7 @@ static int __init inet_init(void)
>  	 */
>
>  	ip_init();
> -
> +#endif /* CONFIG_IPV4 */

[Severity: Critical]
Does this leave peer_cachep NULL on IPV4=n kernels?

ip_init() is the only caller of inet_initpeers(), and inet_initpeers()
is the only place that sets peer_cachep:

net/ipv4/inetpeer.c:inet_initpeers() {
    ...
	peer_cachep = KMEM_CACHE(inet_peer, SLAB_HWCACHE_ALIGN | SLAB_PANIC);
}

inetpeer.o is still built for every INET kernel. IPv6 still uses it
through inet_getpeer_v6(), called from icmpv6_xrlim_allow(),
ndisc_send_redirect() and ip6_forward().

On a lookup miss, inet_getpeer() does:

	p = kmem_cache_alloc(peer_cachep, GFP_ATOMIC);

kmem_cache_alloc_noprof() then dereferences s->object_size on the NULL
cache.

A remote host could trigger this on an IPv6-only kernel by sending a
UDPv6 datagram to a closed port:

__udp6_lib_rcv()
  icmpv6_send(ICMPV6_DEST_UNREACH)
    icmp6_send()
      icmpv6_xrlim_allow()
        inet_getpeer_v6(net->ipv6.peers, &fl6->daddr)
          inet_getpeer()
            kmem_cache_alloc(NULL, GFP_ATOMIC)

DEST_UNREACH is in the default icmpv6_ratemask, so any non-loopback
destination goes through the peer lookup.

At this commit CONFIG_IPV4 is still a hidden def_bool y, so the problem
is latent. However, ip_init() is still inside inet4_init() at the end of
the series, and 'ipv4: make CONFIG_IPV4 boolean' makes IPV4=n
selectable.

Should inet_initpeers() be called outside the IPv4-only block?

[ ... ]

> diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
> index f0efdc13baf4e..f220eaab085b1 100644
> --- a/net/ipv6/af_inet6.c
> +++ b/net/ipv6/af_inet6.c
> @@ -302,6 +302,11 @@ int __inet6_bind(struct sock *sk, struct sockaddr_unsized *uaddr, int addr_len,
>  		struct net_device *dev = NULL;
>  		int chk_addr_ret;
>
> +		if (!IS_ENABLED(CONFIG_IPV4)) {
> +			err = -EADDRNOTAVAIL;
> +			goto out;
> +		}
> +

[Severity: Low]
The commit message says "The same guard is added to reject IPv4-mapped
IPv6". However, the guard is only added to __inet6_bind() and
__ip6_datagram_connect().

At this commit, tcp_v6_connect(), udpv6_sendmsg() and SOL_IP setsockopt
on IPv6 sockets still dispatch to IPv4 code.

There is no intermediate regression, because CONFIG_IPV4 is still a
hidden def_bool y here. Later patches in the series add the missing
guards:

  - tcp_v6_connect(): 'tcp: move protocol agnostic TCP functions out of
    tcp_ipv4.c'
  - udpv6_sendmsg(): 'ipv4: udp: split IPv4 specific logic into
    udp_ipv4.c'
  - ip_setsockopt() and ip_getsockopt(): -EAFNOSUPPORT stubs in
    include/net/ip.h

Could the commit message say more precisely which paths this patch
covers?

[ ... ]

-- 
Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260928193046.6698-1-fmancera%40suse.de