Date:   Thu, 14 Oct 2021 01:20:25 +0200
From:   Dmytro Shytyi <dmytro@...tyi.net>
To:     "Jakub Kicinski" <kuba@...nel.org>,
        "yoshfuji" <yoshfuji@...ux-ipv6.org>,
        "kuznet" <kuznet@....inr.ac.ru>,
        "liuhangbin" <liuhangbin@...il.com>, "davem" <davem@...emloft.net>,
        "netdev" <netdev@...r.kernel.org>,
        "linux-kernel" <linux-kernel@...r.kernel.org>,
        "ek" <ek@...gle.com>, "Jscherpelz" <jscherpelz@...gle.com>
Subject: Re: [PATCH net-next V10] net: Variable SLAAC: SLAAC with prefixes
 of arbitrary length in PIO

Hello Jakub, Eric, All,

Jakub,
> +retry:
> +    spin_lock_bh(&lock);
> +    if (stable_privacy_mode) {
> +        sha1_init(digest);
> +        memset(&data, 0, sizeof(data));
> +        memset(workspace, 0, sizeof(workspace));
> +        memcpy(data.hwaddr, idev->dev->perm_addr, idev->dev->addr_len);
> +        data.prefix[0] = address->s6_addr32[0];
> +        data.prefix[1] = address->s6_addr32[1];
> +        data.secret = secret;
> +        data.dad_count = dad_count;
> +
> +        sha1_transform(digest, data.__data, workspace);
> +
> +        temp.s6_addr32[0] = (__force __be32)digest[0];
> +        temp.s6_addr32[1] = (__force __be32)digest[1];
> +        temp.s6_addr32[2] = (__force __be32)digest[2];
> +        temp.s6_addr32[3] = (__force __be32)digest[3];
> +    } else {
> +        get_random_bytes(temp.s6_addr32, 16);
> +    }
> +
> +    spin_unlock_bh(&lock);

>Is there a reason this code declares all this state on the stack and
>protects it with a lock rather than just allocating the memory with
>kmalloc()?

As you proposed earlier, in "PATCH net-next V10" the memory is allocated with kmalloc.

Eric,
This patch solves "Race to the bottom"  problem  in  VSLAAC. 

Thank you!
                              
Best Regards,
Dmytro SHYTYI

---- On Thu, 14 Oct 2021 01:03:00 +0200 Dmytro Shytyi <dmytro@...tyi.net> wrote ----

 > Variable SLAAC: 
 > [Disabled by default. Can be activated via sysctl] 
 > ["Race to the bottom" problem is solved] 
 > SLAAC with prefixes of arbitrary length in PIO (randomly 
 > generated hostID or stable privacy + privacy extensions). 
 > The main problem is that SLAAC RA allocates a /64 by the Wireless 
 > carrier 4G, 5G to a mobile hotspot, however segmentation of shorter net- 
 > work prefix (ex. /48) is required so that downstream interfaces can be further 
 > subnetted. 
 > Example: uCPE device (4G + WI-FI enabled) receives /48 via Wireless, and 
 > assigns /56 to VNF-Firewall, /56 to WIFI, /56 to Load-Balancer 
 > and /56 to wired connected devices. 
 > IETF document that defines problem statement: 
 > draft-mishra-v6ops-variable-slaac-problem-stmt 
 > IETF document that specifies variable slaac: 
 > draft-mishra-6man-variable-slaac 
 >  
 > Signed-off-by: Dmytro Shytyi <dmytro@...tyi.net> 
 > --- 
 > diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h 
 > index ef4a69865737..076d99874797 100644 
 > --- a/include/linux/ipv6.h 
 > +++ b/include/linux/ipv6.h 
 > @@ -79,6 +79,7 @@ struct ipv6_devconf { 
 >      __u32        ioam6_id; 
 >      __u32        ioam6_id_wide; 
 >      __u8        ioam6_enabled; 
 > +    __s32        variable_slaac; 
 >  
 >      struct ctl_table_header *sysctl_header; 
 >  }; 
 > diff --git a/include/uapi/linux/ipv6.h b/include/uapi/linux/ipv6.h 
 > index b243a53fa985..25606c267809 100644 
 > --- a/include/uapi/linux/ipv6.h 
 > +++ b/include/uapi/linux/ipv6.h 
 > @@ -193,6 +193,7 @@ enum { 
 >      DEVCONF_IOAM6_ENABLED, 
 >      DEVCONF_IOAM6_ID, 
 >      DEVCONF_IOAM6_ID_WIDE, 
 > +    DEVCONF_VARIABLE_SLAAC, 
 >      DEVCONF_MAX 
 >  }; 
 >  
 > diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c 
 > index c6a90b7bbb70..34a12d7f4fb8 100644 
 > --- a/net/ipv6/addrconf.c 
 > +++ b/net/ipv6/addrconf.c 
 > @@ -241,6 +241,7 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = { 
 >      .ioam6_enabled        = 0, 
 >      .ioam6_id               = IOAM6_DEFAULT_IF_ID, 
 >      .ioam6_id_wide        = IOAM6_DEFAULT_IF_ID_WIDE, 
 > +    .variable_slaac        = 0, 
 >  }; 
 >  
 >  static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = { 
 > @@ -300,6 +301,7 @@ static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = { 
 >      .ioam6_enabled        = 0, 
 >      .ioam6_id               = IOAM6_DEFAULT_IF_ID, 
 >      .ioam6_id_wide        = IOAM6_DEFAULT_IF_ID_WIDE, 
 > +    .variable_slaac        = 0, 
 >  }; 
 >  
 >  /* Check if link is ready: is it up and is a valid qdisc available */ 
 > @@ -1349,9 +1351,15 @@ static int ipv6_create_tempaddr(struct inet6_ifaddr *ifp, bool block) 
 >          goto out; 
 >      } 
 >      in6_ifa_hold(ifp); 
 > -    memcpy(addr.s6_addr, ifp->addr.s6_addr, 8); 
 > -    ipv6_gen_rnd_iid(&addr); 
 >  
 > +    if (ifp->prefix_len == 64) { 
 > +        memcpy(addr.s6_addr, ifp->addr.s6_addr, 8); 
 > +        ipv6_gen_rnd_iid(&addr); 
 > +    } else if (ifp->prefix_len > 0 && ifp->prefix_len < 64 && 
 > +           idev->cnf.variable_slaac) { 
 > +        get_random_bytes(addr.s6_addr, 16); 
 > +        ipv6_addr_prefix_copy(&addr, &ifp->addr, ifp->prefix_len); 
 > +    } 
 >      age = (now - ifp->tstamp) / HZ; 
 >  
 >      regen_advance = idev->cnf.regen_max_retry * 
 > @@ -2579,6 +2587,31 @@ static bool is_addr_mode_generate_stable(struct inet6_dev *idev) 
 >             idev->cnf.addr_gen_mode == IN6_ADDR_GEN_MODE_RANDOM; 
 >  } 
 >  
 > +static struct inet6_ifaddr *ipv6_cmp_rcvd_prsnt_prfxs(struct inet6_ifaddr *ifp, 
 > +                              struct inet6_dev *in6_dev, 
 > +                              struct net *net, 
 > +                              const struct prefix_info *pinfo) 
 > +{ 
 > +    struct inet6_ifaddr *result = NULL; 
 > +    bool prfxs_equal; 
 > + 
 > +    rcu_read_lock(); 
 > +    list_for_each_entry_rcu(ifp, &in6_dev->addr_list, if_list) { 
 > +        if (!net_eq(dev_net(ifp->idev->dev), net)) 
 > +            continue; 
 > +        prfxs_equal = 
 > +            ipv6_prefix_equal(&pinfo->prefix, &ifp->addr, pinfo->prefix_len); 
 > +        if (prfxs_equal && pinfo->prefix_len == ifp->prefix_len) { 
 > +            result = ifp; 
 > +            in6_ifa_hold(ifp); 
 > +            break; 
 > +        } 
 > +    } 
 > +    rcu_read_unlock(); 
 > + 
 > +    return result; 
 > +} 
 > + 
 >  int addrconf_prefix_rcv_add_addr(struct net *net, struct net_device *dev, 
 >                   const struct prefix_info *pinfo, 
 >                   struct inet6_dev *in6_dev, 
 > @@ -2586,9 +2619,17 @@ int addrconf_prefix_rcv_add_addr(struct net *net, struct net_device *dev, 
 >                   u32 addr_flags, bool sllao, bool tokenized, 
 >                   __u32 valid_lft, u32 prefered_lft) 
 >  { 
 > -    struct inet6_ifaddr *ifp = ipv6_get_ifaddr(net, addr, dev, 1); 
 > +    struct inet6_ifaddr *ifp = NULL; 
 > +    int plen = pinfo->prefix_len; 
 >      int create = 0; 
 >  
 > +    if (plen > 0 && plen < 64 && 
 > +        in6_dev->cnf.addr_gen_mode != IN6_ADDR_GEN_MODE_STABLE_PRIVACY && 
 > +        in6_dev->cnf.variable_slaac) 
 > +        ifp = ipv6_cmp_rcvd_prsnt_prfxs(ifp, in6_dev, net, pinfo); 
 > +    else 
 > +        ifp = ipv6_get_ifaddr(net, addr, dev, 1); 
 > + 
 >      if (!ifp && valid_lft) { 
 >          int max_addresses = in6_dev->cnf.max_addresses; 
 >          struct ifa6_config cfg = { 
 > @@ -2667,6 +2708,94 @@ int addrconf_prefix_rcv_add_addr(struct net *net, struct net_device *dev, 
 >  } 
 >  EXPORT_SYMBOL_GPL(addrconf_prefix_rcv_add_addr); 
 >  
 > +static bool ipv6_reserved_interfaceid(struct in6_addr address) 
 > +{ 
 > +    if ((address.s6_addr32[2] | address.s6_addr32[3]) == 0) 
 > +        return true; 
 > + 
 > +    if (address.s6_addr32[2] == htonl(0x02005eff) && 
 > +        ((address.s6_addr32[3] & htonl(0xfe000000)) == htonl(0xfe000000))) 
 > +        return true; 
 > + 
 > +    if (address.s6_addr32[2] == htonl(0xfdffffff) && 
 > +        ((address.s6_addr32[3] & htonl(0xffffff80)) == htonl(0xffffff80))) 
 > +        return true; 
 > + 
 > +    return false; 
 > +} 
 > + 
 > +static int ipv6_gen_addr_var_plen(struct in6_addr *address, 
 > +                  u8 dad_count, 
 > +                  const struct inet6_dev *idev, 
 > +                  unsigned int rcvd_prfx_len, 
 > +                  bool stable_privacy_mode) 
 > +{ 
 > +    union data_union { 
 > +        char __data[SHA1_BLOCK_SIZE]; 
 > +        struct { 
 > +            struct in6_addr secret; 
 > +            __be32 prefix[2]; 
 > +            unsigned char hwaddr[MAX_ADDR_LEN]; 
 > +            u8 dad_count; 
 > +        } __packed; 
 > +    }; 
 > +    union data_union *data; 
 > +    struct in6_addr *secret; 
 > +    struct in6_addr *temp; 
 > +    struct net *net; 
 > +    int *workspace; 
 > +    int *digest; 
 > + 
 > +    workspace = kmalloc_array(SHA1_WORKSPACE_WORDS, sizeof(__u32), GFP_KERNEL); 
 > +    digest = kmalloc_array(SHA1_DIGEST_WORDS, sizeof(__u32), GFP_KERNEL); 
 > +    data = kmalloc(sizeof(*data), GFP_KERNEL); 
 > +    secret = kmalloc(sizeof(*secret), GFP_KERNEL); 
 > +    temp = kmalloc(sizeof(*temp), GFP_KERNEL); 
 > +    net = dev_net(idev->dev); 
 > + 
 > +    BUILD_BUG_ON(sizeof(data->__data) != sizeof(*data)); 
 > + 
 > +    if (stable_privacy_mode) { 
 > +        if (idev->cnf.stable_secret.initialized) 
 > +            *secret = idev->cnf.stable_secret.secret; 
 > +        else if (net->ipv6.devconf_dflt->stable_secret.initialized) 
 > +            *secret = net->ipv6.devconf_dflt->stable_secret.secret; 
 > +        else 
 > +            return -1; 
 > +    } 
 > + 
 > +retry: 
 > +    if (stable_privacy_mode) { 
 > +        sha1_init(digest); 
 > +        memset(data, 0, sizeof(*data)); 
 > +        memset(workspace, 0, sizeof(*workspace)); 
 > +        memcpy(data->hwaddr, idev->dev->perm_addr, idev->dev->addr_len); 
 > +        data->prefix[0] = address->s6_addr32[0]; 
 > +        data->prefix[1] = address->s6_addr32[1]; 
 > +        data->secret = *secret; 
 > +        data->dad_count = dad_count; 
 > + 
 > +        sha1_transform(digest, data->__data, workspace); 
 > + 
 > +        temp->s6_addr32[0] = (__force __be32)digest[0]; 
 > +        temp->s6_addr32[1] = (__force __be32)digest[1]; 
 > +        temp->s6_addr32[2] = (__force __be32)digest[2]; 
 > +        temp->s6_addr32[3] = (__force __be32)digest[3]; 
 > +    } else { 
 > +        get_random_bytes(temp->s6_addr32, 16); 
 > +    } 
 > + 
 > +    if (ipv6_reserved_interfaceid(*temp)) { 
 > +        dad_count++; 
 > +        if (dad_count > dev_net(idev->dev)->ipv6.sysctl.idgen_retries) 
 > +            return -1; 
 > +        goto retry; 
 > +    } 
 > +    ipv6_addr_prefix_copy(temp, address, rcvd_prfx_len); 
 > +    *address = *temp; 
 > +    return 0; 
 > +} 
 > + 
 >  void addrconf_prefix_rcv(struct net_device *dev, u8 *opt, int len, bool sllao) 
 >  { 
 >      struct prefix_info *pinfo; 
 > @@ -2791,9 +2920,33 @@ void addrconf_prefix_rcv(struct net_device *dev, u8 *opt, int len, bool sllao) 
 >                  dev_addr_generated = true; 
 >              } 
 >              goto ok; 
 > +        } else if (pinfo->prefix_len > 0 && pinfo->prefix_len < 64 && 
 > +               in6_dev->cnf.variable_slaac) { 
 > +            /* SLAAC with prefixes of arbitrary length (Variable SLAAC). 
 > +             * draft-mishra-6man-variable-slaac 
 > +             * draft-mishra-v6ops-variable-slaac-problem-stmt 
 > +             */ 
 > +            memcpy(&addr, &pinfo->prefix, 16); 
 > +            if (in6_dev->cnf.addr_gen_mode == IN6_ADDR_GEN_MODE_STABLE_PRIVACY) { 
 > +                if (!ipv6_gen_addr_var_plen(&addr, 
 > +                                0, 
 > +                                in6_dev, 
 > +                                pinfo->prefix_len, 
 > +                                true)) { 
 > +                    addr_flags |= IFA_F_STABLE_PRIVACY; 
 > +                    goto ok; 
 > +                } 
 > +            } else if (!ipv6_gen_addr_var_plen(&addr, 
 > +                               0, 
 > +                               in6_dev, 
 > +                               pinfo->prefix_len, 
 > +                               false)) { 
 > +                goto ok; 
 > +            } 
 > +        } else { 
 > +            net_dbg_ratelimited("IPv6: Prefix with unexpected length %d\n", 
 > +                        pinfo->prefix_len); 
 >          } 
 > -        net_dbg_ratelimited("IPv6 addrconf: prefix with wrong length %d\n", 
 > -                    pinfo->prefix_len); 
 >          goto put; 
 >  
 >  ok: 
 > @@ -5542,6 +5679,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf, 
 >      array[DEVCONF_IOAM6_ENABLED] = cnf->ioam6_enabled; 
 >      array[DEVCONF_IOAM6_ID] = cnf->ioam6_id; 
 >      array[DEVCONF_IOAM6_ID_WIDE] = cnf->ioam6_id_wide; 
 > +    array[DEVCONF_VARIABLE_SLAAC] = cnf->variable_slaac; 
 >  } 
 >  
 >  static inline size_t inet6_ifla6_size(void) 
 > @@ -6905,6 +7043,13 @@ static const struct ctl_table addrconf_sysctl[] = { 
 >          .proc_handler    = proc_dointvec, 
 >  
 >      }, 
 > +    { 
 > +        .procname    = "variable_slaac", 
 > +        .data        = &ipv6_devconf.variable_slaac, 
 > +        .maxlen        = sizeof(int), 
 > +        .mode        = 0644, 
 > +        .proc_handler    = proc_dointvec, 
 > +    }, 
 >      { 
 >          .procname    = "seg6_enabled", 
 >          .data        = &ipv6_devconf.seg6_enabled, 
 >  
 > 

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