net: icmp: pass zeroed opts from icmp{,v6}_ndo_send before sending

commit ee576c47db60432c37e54b1e2b43a8ca6d3a8dca upstream.

The icmp{,v6}_send functions make all sorts of use of skb->cb, casting
it with IPCB or IP6CB, assuming the skb to have come directly from the
inet layer. But when the packet comes from the ndo layer, especially
when forwarded, there's no telling what might be in skb->cb at that
point. As a result, the icmp sending code risks reading bogus memory
contents, which can result in nasty stack overflows such as this one
reported by a user:

    panic+0x108/0x2ea
    __stack_chk_fail+0x14/0x20
    __icmp_send+0x5bd/0x5c0
    icmp_ndo_send+0x148/0x160

In icmp_send, skb->cb is cast with IPCB and an ip_options struct is read
from it. The optlen parameter there is of particular note, as it can
induce writes beyond bounds. There are quite a few ways that can happen
in __ip_options_echo. For example:

    // sptr/skb are attacker-controlled skb bytes
    sptr = skb_network_header(skb);
    // dptr/dopt points to stack memory allocated by __icmp_send
    dptr = dopt->__data;
    // sopt is the corrupt skb->cb in question
    if (sopt->rr) {
        optlen  = sptr[sopt->rr+1]; // corrupt skb->cb + skb->data
        soffset = sptr[sopt->rr+2]; // corrupt skb->cb + skb->data
	// this now writes potentially attacker-controlled data, over
	// flowing the stack:
        memcpy(dptr, sptr+sopt->rr, optlen);
    }

In the icmpv6_send case, the story is similar, but not as dire, as only
IP6CB(skb)->iif and IP6CB(skb)->dsthao are used. The dsthao case is
worse than the iif case, but it is passed to ipv6_find_tlv, which does
a bit of bounds checking on the value.

This is easy to simulate by doing a `memset(skb->cb, 0x41,
sizeof(skb->cb));` before calling icmp{,v6}_ndo_send, and it's only by
good fortune and the rarity of icmp sending from that context that we've
avoided reports like this until now. For example, in KASAN:

    BUG: KASAN: stack-out-of-bounds in __ip_options_echo+0xa0e/0x12b0
    Write of size 38 at addr ffff888006f1f80e by task ping/89
    CPU: 2 PID: 89 Comm: ping Not tainted 5.10.0-rc7-debug+ #5
    Call Trace:
     dump_stack+0x9a/0xcc
     print_address_description.constprop.0+0x1a/0x160
     __kasan_report.cold+0x20/0x38
     kasan_report+0x32/0x40
     check_memory_region+0x145/0x1a0
     memcpy+0x39/0x60
     __ip_options_echo+0xa0e/0x12b0
     __icmp_send+0x744/0x1700

Actually, out of the 4 drivers that do this, only gtp zeroed the cb for
the v4 case, while the rest did not. So this commit actually removes the
gtp-specific zeroing, while putting the code where it belongs in the
shared infrastructure of icmp{,v6}_ndo_send.

This commit fixes the issue by passing an empty IPCB or IP6CB along to
the functions that actually do the work. For the icmp_send, this was
already trivial, thanks to __icmp_send providing the plumbing function.
For icmpv6_send, this required a tiny bit of refactoring to make it
behave like the v4 case, after which it was straight forward.

Fixes: a2b78e9b2cac ("sunvnet: generate ICMP PTMUD messages for smaller port MTUs")
Reported-by: SinYu <liuxyon@gmail.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/netdev/CAF=yD-LOF116aHub6RMe8vB8ZpnrrnoTdqhobEx+bvoA8AsP0w@mail.gmail.com/T/
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Link: https://lore.kernel.org/r/20210223131858.72082-1-Jason@zx2c4.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c
index 857c5ba3bead76616f550118c1211d1bf6e8857c..e513736ae0d536d4dc223073a0e0f27ff2ee6b8d 100644 (file)
--- a/drivers/net/gtp.c
+++ b/drivers/net/gtp.c
@@ -559,7 +559,6 @@ static int gtp_build_skb_ip4(struct sk_buff *skb, struct net_device *dev,
        if (!skb_is_gso(skb) && (iph->frag_off & htons(IP_DF)) &&
            mtu < ntohs(iph->tot_len)) {
                netdev_dbg(dev, "packet too big, fragmentation needed\n");
-               memset(IPCB(skb), 0, sizeof(*IPCB(skb)));
                icmp_ndo_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
                              htonl(mtu));
                goto err_rt;

diff --git a/include/linux/icmpv6.h b/include/linux/icmpv6.h
index e09e471e470459cdf82ab40a212bfaf9cf63aafe..d87dabac04c1ba083be0026023ca999e4eacd4ae 100644 (file)
--- a/include/linux/icmpv6.h
+++ b/include/linux/icmpv6.h
@@ -2,6 +2,7 @@
 #define _LINUX_ICMPV6_H
 
 #include <linux/skbuff.h>
+#include <linux/ipv6.h>
 #include <uapi/linux/icmpv6.h>
 
 static inline struct icmp6hdr *icmp6_hdr(const struct sk_buff *skb)
@@ -14,13 +15,16 @@ static inline struct icmp6hdr *icmp6_hdr(const struct sk_buff *skb)
 #if IS_ENABLED(CONFIG_IPV6)
 
 typedef void ip6_icmp_send_t(struct sk_buff *skb, u8 type, u8 code, __u32 info,
-                            const struct in6_addr *force_saddr);
+                            const struct in6_addr *force_saddr,
+                            const struct inet6_skb_parm *parm);
 void icmp6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info,
-               const struct in6_addr *force_saddr);
+               const struct in6_addr *force_saddr,
+               const struct inet6_skb_parm *parm);
 #if IS_BUILTIN(CONFIG_IPV6)
-static inline void icmpv6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info)
+static inline void __icmpv6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info,
+                                const struct inet6_skb_parm *parm)
 {
-       icmp6_send(skb, type, code, info, NULL);
+       icmp6_send(skb, type, code, info, NULL, parm);
 }
 static inline int inet6_register_icmp_sender(ip6_icmp_send_t *fn)
 {
@@ -33,18 +37,28 @@ static inline int inet6_unregister_icmp_sender(ip6_icmp_send_t *fn)
        return 0;
 }
 #else
-extern void icmpv6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info);
+extern void __icmpv6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info,
+                         const struct inet6_skb_parm *parm);
 extern int inet6_register_icmp_sender(ip6_icmp_send_t *fn);
 extern int inet6_unregister_icmp_sender(ip6_icmp_send_t *fn);
 #endif
 
+static inline void icmpv6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info)
+{
+       __icmpv6_send(skb, type, code, info, IP6CB(skb));
+}
+
 int ip6_err_gen_icmpv6_unreach(struct sk_buff *skb, int nhs, int type,
                               unsigned int data_len);
 
 #if IS_ENABLED(CONFIG_NF_NAT)
 void icmpv6_ndo_send(struct sk_buff *skb_in, u8 type, u8 code, __u32 info);
 #else
-#define icmpv6_ndo_send icmpv6_send
+static inline void icmpv6_ndo_send(struct sk_buff *skb_in, u8 type, u8 code, __u32 info)
+{
+       struct inet6_skb_parm parm = { 0 };
+       __icmpv6_send(skb_in, type, code, info, &parm);
+}
 #endif
 
 #else

diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index b9dfca557a6c26795cb5e237a7c508345fcc3b3f..97a4e1667f73dd297554fb2b467a7473ef51c6c2 100644 (file)
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -2,6 +2,7 @@
 #define _IPV6_H
 
 #include <uapi/linux/ipv6.h>
+#include <uapi/linux/icmpv6.h>
 
 #define ipv6_optlen(p)  (((p)->hdrlen+1) << 3)
 #define ipv6_authlen(p) (((p)->hdrlen+2) << 2)
@@ -73,7 +74,6 @@ struct ipv6_params {
        __s32 autoconf;
 };
 extern struct ipv6_params ipv6_defaults;
-#include <linux/icmpv6.h>
 #include <linux/tcp.h>
 #include <linux/udp.h>
 

diff --git a/include/net/icmp.h b/include/net/icmp.h
index 9c344e2655d2cbeb4f12f181353e769faba9fe95..ffe4a5d2bbe7e247c0570cadff56e79a75abef45 100644 (file)
--- a/include/net/icmp.h
+++ b/include/net/icmp.h
@@ -50,7 +50,11 @@ static inline void icmp_send(struct sk_buff *skb_in, int type, int code, __be32
 #if IS_ENABLED(CONFIG_NF_NAT)
 void icmp_ndo_send(struct sk_buff *skb_in, int type, int code, __be32 info);
 #else
-#define icmp_ndo_send icmp_send
+static inline void icmp_ndo_send(struct sk_buff *skb_in, int type, int code, __be32 info)
+{
+       struct ip_options opts = { 0 };
+       __icmp_send(skb_in, type, code, info, &opts);
+}
 #endif
 
 int icmp_rcv(struct sk_buff *skb);

diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 545947b380054f31caafaed86c31991f80295945..27518ea7ec3c87b4a3f3e31ac5eda102efcc7617 100644 (file)
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -743,13 +743,14 @@ EXPORT_SYMBOL(__icmp_send);
 void icmp_ndo_send(struct sk_buff *skb_in, int type, int code, __be32 info)
 {
        struct sk_buff *cloned_skb = NULL;
+       struct ip_options opts = { 0 };
        enum ip_conntrack_info ctinfo;
        struct nf_conn *ct;
        __be32 orig_ip;
 
        ct = nf_ct_get(skb_in, &ctinfo);
        if (!ct || !(ct->status & IPS_SRC_NAT)) {
-               icmp_send(skb_in, type, code, info);
+               __icmp_send(skb_in, type, code, info, &opts);
                return;
        }
 
@@ -764,7 +765,7 @@ void icmp_ndo_send(struct sk_buff *skb_in, int type, int code, __be32 info)
 
        orig_ip = ip_hdr(skb_in)->saddr;
        ip_hdr(skb_in)->saddr = ct->tuplehash[0].tuple.src.u3.ip;
-       icmp_send(skb_in, type, code, info);
+       __icmp_send(skb_in, type, code, info, &opts);
        ip_hdr(skb_in)->saddr = orig_ip;
 out:
        consume_skb(cloned_skb);

diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index 43f44398d0b3be63e28dfef92f08b4e391ed9489..c879a8202286e23a83d26974f75fa52399b88726 100644 (file)
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -298,10 +298,9 @@ static int icmpv6_getfrag(void *from, char *to, int offset, int len, int odd, st
 }
 
 #if IS_ENABLED(CONFIG_IPV6_MIP6)
-static void mip6_addr_swap(struct sk_buff *skb)
+static void mip6_addr_swap(struct sk_buff *skb, const struct inet6_skb_parm *opt)
 {
        struct ipv6hdr *iph = ipv6_hdr(skb);
-       struct inet6_skb_parm *opt = IP6CB(skb);
        struct ipv6_destopt_hao *hao;
        struct in6_addr tmp;
        int off;
@@ -318,7 +317,7 @@ static void mip6_addr_swap(struct sk_buff *skb)
        }
 }
 #else
-static inline void mip6_addr_swap(struct sk_buff *skb) {}
+static inline void mip6_addr_swap(struct sk_buff *skb, const struct inet6_skb_parm *opt) {}
 #endif
 
 static struct dst_entry *icmpv6_route_lookup(struct net *net,
@@ -389,7 +388,8 @@ relookup_failed:
  *     Send an ICMP message in response to a packet in error
  */
 void icmp6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info,
-               const struct in6_addr *force_saddr)
+               const struct in6_addr *force_saddr,
+               const struct inet6_skb_parm *parm)
 {
        struct net *net = dev_net(skb->dev);
        struct inet6_dev *idev = NULL;
@@ -473,7 +473,7 @@ void icmp6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info,
                return;
        }
 
-       mip6_addr_swap(skb);
+       mip6_addr_swap(skb, parm);
 
        memset(&fl6, 0, sizeof(fl6));
        fl6.flowi6_proto = IPPROTO_ICMPV6;
@@ -556,7 +556,7 @@ out:
  */
 void icmpv6_param_prob(struct sk_buff *skb, u8 code, int pos)
 {
-       icmp6_send(skb, ICMPV6_PARAMPROB, code, pos, NULL);
+       icmp6_send(skb, ICMPV6_PARAMPROB, code, pos, NULL, IP6CB(skb));
        kfree_skb(skb);
 }
 EXPORT_SYMBOL(icmp6_send);
@@ -613,10 +613,10 @@ int ip6_err_gen_icmpv6_unreach(struct sk_buff *skb, int nhs, int type,
        }
        if (type == ICMP_TIME_EXCEEDED)
                icmp6_send(skb2, ICMPV6_TIME_EXCEED, ICMPV6_EXC_HOPLIMIT,
-                          info, &temp_saddr);
+                          info, &temp_saddr, IP6CB(skb2));
        else
                icmp6_send(skb2, ICMPV6_DEST_UNREACH, ICMPV6_ADDR_UNREACH,
-                          info, &temp_saddr);
+                          info, &temp_saddr, IP6CB(skb2));
        if (rt)
                ip6_rt_put(rt);
 

diff --git a/net/ipv6/ip6_icmp.c b/net/ipv6/ip6_icmp.c
index e9b109d7b47f88dafd7cb792f2b4485ef921ae8d..05287bc36dbdf3dcc5504e5677910e10db027e69 100644 (file)
--- a/net/ipv6/ip6_icmp.c
+++ b/net/ipv6/ip6_icmp.c
@@ -32,23 +32,25 @@ int inet6_unregister_icmp_sender(ip6_icmp_send_t *fn)
 }
 EXPORT_SYMBOL(inet6_unregister_icmp_sender);
 
-void icmpv6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info)
+void __icmpv6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info,
+                  const struct inet6_skb_parm *parm)
 {
        ip6_icmp_send_t *send;
 
        rcu_read_lock();
        send = rcu_dereference(ip6_icmp_send);
        if (send)
-               send(skb, type, code, info, NULL);
+               send(skb, type, code, info, NULL, parm);
        rcu_read_unlock();
 }
-EXPORT_SYMBOL(icmpv6_send);
+EXPORT_SYMBOL(__icmpv6_send);
 #endif
 
 #if IS_ENABLED(CONFIG_NF_NAT)
 #include <net/netfilter/nf_conntrack.h>
 void icmpv6_ndo_send(struct sk_buff *skb_in, u8 type, u8 code, __u32 info)
 {
+       struct inet6_skb_parm parm = { 0 };
        struct sk_buff *cloned_skb = NULL;
        enum ip_conntrack_info ctinfo;
        struct in6_addr orig_ip;
@@ -56,7 +58,7 @@ void icmpv6_ndo_send(struct sk_buff *skb_in, u8 type, u8 code, __u32 info)
 
        ct = nf_ct_get(skb_in, &ctinfo);
        if (!ct || !(ct->status & IPS_SRC_NAT)) {
-               icmpv6_send(skb_in, type, code, info);
+               __icmpv6_send(skb_in, type, code, info, &parm);
                return;
        }
 
@@ -71,7 +73,7 @@ void icmpv6_ndo_send(struct sk_buff *skb_in, u8 type, u8 code, __u32 info)
 
        orig_ip = ipv6_hdr(skb_in)->saddr;
        ipv6_hdr(skb_in)->saddr = ct->tuplehash[0].tuple.src.u3.in6;
-       icmpv6_send(skb_in, type, code, info);
+       __icmpv6_send(skb_in, type, code, info, &parm);
        ipv6_hdr(skb_in)->saddr = orig_ip;
 out:
        consume_skb(cloned_skb);