kernel/linux.git/net/ipv6/datagram.c, branch v6.1.168

ipv6: avoid overflows in ip6_datagram_send_ctl()

2026-04-11T12:16:24+00:00

[ Upstream commit 4e453375561fc60820e6b9d8ebeb6b3ee177d42e ] Yiming Qian reported : I believe I found a locally triggerable kernel bug in the IPv6 sendmsg ancillary-data path that can panic the kernel via `skb_under_panic()` (local DoS). The core issue is a mismatch between: - a 16-bit length accumulator (`struct ipv6_txoptions::opt_flen`, type `__u16`) and - a pointer to the *last* provided destination-options header (`opt->dst1opt`) when multiple `IPV6_DSTOPTS` control messages (cmsgs) are provided. - `include/net/ipv6.h`: - `struct ipv6_txoptions::opt_flen` is `__u16` (wrap possible). (lines 291-307, especially 298) - `net/ipv6/datagram.c:ip6_datagram_send_ctl()`: - Accepts repeated `IPV6_DSTOPTS` and accumulates into `opt_flen` without rejecting duplicates. (lines 909-933) - `net/ipv6/ip6_output.c:__ip6_append_data()`: - Uses `opt->opt_flen + opt->opt_nflen` to compute header sizes/headroom decisions. (lines 1448-1466, especially 1463-1465) - `net/ipv6/ip6_output.c:__ip6_make_skb()`: - Calls `ipv6_push_frag_opts()` if `opt->opt_flen` is non-zero. (lines 1930-1934) - `net/ipv6/exthdrs.c:ipv6_push_frag_opts()` / `ipv6_push_exthdr()`: - Push size comes from `ipv6_optlen(opt->dst1opt)` (based on the pointed-to header). (lines 1179-1185 and 1206-1211) 1. `opt_flen` is a 16-bit accumulator: - `include/net/ipv6.h:298` defines `__u16 opt_flen; /* after fragment hdr */`. 2. `ip6_datagram_send_ctl()` accepts *repeated* `IPV6_DSTOPTS` cmsgs and increments `opt_flen` each time: - In `net/ipv6/datagram.c:909-933`, for `IPV6_DSTOPTS`: - It computes `len = ((hdr->hdrlen + 1) << 3);` - It checks `CAP_NET_RAW` using `ns_capable(net->user_ns, CAP_NET_RAW)`. (line 922) - Then it does: - `opt->opt_flen += len;` (line 927) - `opt->dst1opt = hdr;` (line 928) There is no duplicate rejection here (unlike the legacy `IPV6_2292DSTOPTS` path which rejects duplicates at `net/ipv6/datagram.c:901-904`). If enough large `IPV6_DSTOPTS` cmsgs are provided, `opt_flen` wraps while `dst1opt` still points to a large (2048-byte) destination-options header. In the attached PoC (`poc.c`): - 32 cmsgs with `hdrlen=255` => `len = (255+1)*8 = 2048` - 1 cmsg with `hdrlen=0` => `len = 8` - Total increment: `32*2048 + 8 = 65544`, so `(__u16)opt_flen == 8` - The last cmsg is 2048 bytes, so `dst1opt` points to a 2048-byte header. 3. The transmit path sizes headers using the wrapped `opt_flen`: - In `net/ipv6/ip6_output.c:1463-1465`: - `headersize = sizeof(struct ipv6hdr) + (opt ? opt->opt_flen + opt->opt_nflen : 0) + ...;` With wrapped `opt_flen`, `headersize`/headroom decisions underestimate what will be pushed later. 4. When building the final skb, the actual push length comes from `dst1opt` and is not limited by wrapped `opt_flen`: - In `net/ipv6/ip6_output.c:1930-1934`: - `if (opt->opt_flen) proto = ipv6_push_frag_opts(skb, opt, proto);` - In `net/ipv6/exthdrs.c:1206-1211`, `ipv6_push_frag_opts()` pushes `dst1opt` via `ipv6_push_exthdr()`. - In `net/ipv6/exthdrs.c:1179-1184`, `ipv6_push_exthdr()` does: - `skb_push(skb, ipv6_optlen(opt));` - `memcpy(h, opt, ipv6_optlen(opt));` With insufficient headroom, `skb_push()` underflows and triggers `skb_under_panic()` -> `BUG()`: - `net/core/skbuff.c:2669-2675` (`skb_push()` calls `skb_under_panic()`) - `net/core/skbuff.c:207-214` (`skb_panic()` ends in `BUG()`) - The `IPV6_DSTOPTS` cmsg path requires `CAP_NET_RAW` in the target netns user namespace (`ns_capable(net->user_ns, CAP_NET_RAW)`). - Root (or any task with `CAP_NET_RAW`) can trigger this without user namespaces. - An unprivileged `uid=1000` user can trigger this if unprivileged user namespaces are enabled and it can create a userns+netns to obtain namespaced `CAP_NET_RAW` (the attached PoC does this). - Local denial of service: kernel BUG/panic (system crash). - Reproducible with a small userspace PoC. This patch does not reject duplicated options, as this might break some user applications. Instead, it makes sure to adjust opt_flen and opt_nflen to correctly reflect the size of the current option headers, preventing the overflows and the potential for panics. This applies to IPV6_DSTOPTS, IPV6_HOPOPTS, and IPV6_RTHDR. Specifically: When a new IPV6_DSTOPTS is processed, the length of the old opt->dst1opt is subtracted from opt->opt_flen before adding the new length. When a new IPV6_HOPOPTS is processed, the length of the old opt->dst0opt is subtracted from opt->opt_nflen. When a new Routing Header (IPV6_RTHDR or IPV6_2292RTHDR) is processed, the length of the old opt->srcrt is subtracted from opt->opt_nflen. In the special case within IPV6_2292RTHDR handling where dst1opt is moved to dst0opt, the length of the old opt->dst0opt is subtracted from opt->opt_nflen before the new one is added. Fixes: 333fad5364d6 ("[IPV6]: Support several new sockopt / ancillary data in Advanced API (RFC3542).") Reported-by: Yiming Qian Closes: https://lore.kernel.org/netdev/CAL_bE8JNzawgr5OX5m+3jnQDHry2XxhQT5=jThW1zDPtUikRYA@mail.gmail.com/ Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20260401154721.3740056-1-edumazet@google.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin

ipv6: Fix datagram socket connection with DSCP.

2023-02-22T11:59:54+00:00

commit e010ae08c71fda8be3d6bda256837795a0b3ea41 upstream. Take into account the IPV6_TCLASS socket option (DSCP) in ip6_datagram_flow_key_init(). Otherwise fib6_rule_match() can't properly match the DSCP value, resulting in invalid route lookup. For example: ip route add unreachable table main 2001:db8::10/124 ip route add table 100 2001:db8::10/124 dev eth0 ip -6 rule add dsfield 0x04 table 100 echo test | socat - UDP6:[2001:db8::11]:54321,ipv6-tclass=0x04 Without this patch, socat fails at connect() time ("No route to host") because the fib-rule doesn't jump to table 100 and the lookup ends up being done in the main table. Fixes: 2cc67cc731d9 ("[IPV6] ROUTE: Routing by Traffic Class.") Signed-off-by: Guillaume Nault Reviewed-by: Eric Dumazet Reviewed-by: David Ahern Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman

net: setsockopt: fix IPV6_UNICAST_IF option for connected sockets

2022-12-31T12:32:27+00:00

[ Upstream commit 526682b458b1b56d2e0db027df535cb5cdcfde59 ] Change the behaviour of ip6_datagram_connect to consider the interface set by the IPV6_UNICAST_IF socket option, similarly to udpv6_sendmsg. This change is the IPv6 counterpart of the fix for IP_UNICAST_IF. The tests introduced by that patch showed that the incorrect behavior is present in IPv6 as well. This patch fixes the broken test. Reported-by: kernel test robot Link: https://lore.kernel.org/r/202210062117.c7eef1a3-oliver.sang@intel.com Fixes: 0e4d354762ce ("net-next: Fix IP_UNICAST_IF option behavior for connected sockets") Signed-off-by: Richard Gobert Reviewed-by: David Ahern Signed-off-by: David S. Miller Signed-off-by: Sasha Levin

udp: Update reuse->has_conns under reuseport_lock.

2022-10-18T08:17:18+00:00

When we call connect() for a UDP socket in a reuseport group, we have to update sk->sk_reuseport_cb->has_conns to 1. Otherwise, the kernel could select a unconnected socket wrongly for packets sent to the connected socket. However, the current way to set has_conns is illegal and possible to trigger that problem. reuseport_has_conns() changes has_conns under rcu_read_lock(), which upgrades the RCU reader to the updater. Then, it must do the update under the updater's lock, reuseport_lock, but it doesn't for now. For this reason, there is a race below where we fail to set has_conns resulting in the wrong socket selection. To avoid the race, let's split the reader and updater with proper locking. cpu1 cpu2 +----+ +----+ __ip[46]_datagram_connect() reuseport_grow() . . |- reuseport_has_conns(sk, true) |- more_reuse = __reuseport_alloc(more_socks_size) | . | | |- rcu_read_lock() | |- reuse = rcu_dereference(sk->sk_reuseport_cb) | | | | | /* reuse->has_conns == 0 here */ | | |- more_reuse->has_conns = reuse->has_conns | |- reuse->has_conns = 1 | /* more_reuse->has_conns SHOULD BE 1 HERE */ | | | | | |- rcu_assign_pointer(reuse->socks[i]->sk_reuseport_cb, | | | more_reuse) | `- rcu_read_unlock() `- kfree_rcu(reuse, rcu) | |- sk->sk_state = TCP_ESTABLISHED Note the likely(reuse) in reuseport_has_conns_set() is always true, but we put the test there for ease of review. [0] For the record, usually, sk_reuseport_cb is changed under lock_sock(). The only exception is reuseport_grow() & TCP reqsk migration case. 1) shutdown() TCP listener, which is moved into the latter part of reuse->socks[] to migrate reqsk. 2) New listen() overflows reuse->socks[] and call reuseport_grow(). 3) reuse->max_socks overflows u16 with the new listener. 4) reuseport_grow() pops the old shutdown()ed listener from the array and update its sk->sk_reuseport_cb as NULL without lock_sock(). shutdown()ed TCP sk->sk_reuseport_cb can be changed without lock_sock(), but, reuseport_has_conns_set() is called only for UDP under lock_sock(), so likely(reuse) never be false in reuseport_has_conns_set(). [0]: https://lore.kernel.org/netdev/CANn89iLja=eQHbsM_Ta2sQF0tOGU8vAGrh_izRuuHjuO1ouUag@mail.gmail.com/ Fixes: acdcecc61285 ("udp: correct reuseport selection with connected sockets") Signed-off-by: Kuniyuki Iwashima Link: https://lore.kernel.org/r/20221014182625.89913-1-kuniyu@amazon.com Signed-off-by: Paolo Abeni

net: annotate races around sk->sk_bound_dev_if

2022-05-16T09:31:05+00:00

UDP sendmsg() is lockless, and reads sk->sk_bound_dev_if while this field can be changed by another thread. Adds minimal annotations to avoid KCSAN splats for UDP. Following patches will add more annotations to potential lockless readers. BUG: KCSAN: data-race in __ip6_datagram_connect / udpv6_sendmsg write to 0xffff888136d47a94 of 4 bytes by task 7681 on cpu 0: __ip6_datagram_connect+0x6e2/0x930 net/ipv6/datagram.c:221 ip6_datagram_connect+0x2a/0x40 net/ipv6/datagram.c:272 inet_dgram_connect+0x107/0x190 net/ipv4/af_inet.c:576 __sys_connect_file net/socket.c:1900 [inline] __sys_connect+0x197/0x1b0 net/socket.c:1917 __do_sys_connect net/socket.c:1927 [inline] __se_sys_connect net/socket.c:1924 [inline] __x64_sys_connect+0x3d/0x50 net/socket.c:1924 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x2b/0x50 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae read to 0xffff888136d47a94 of 4 bytes by task 7670 on cpu 1: udpv6_sendmsg+0xc60/0x16e0 net/ipv6/udp.c:1436 inet6_sendmsg+0x5f/0x80 net/ipv6/af_inet6.c:652 sock_sendmsg_nosec net/socket.c:705 [inline] sock_sendmsg net/socket.c:725 [inline] ____sys_sendmsg+0x39a/0x510 net/socket.c:2413 ___sys_sendmsg net/socket.c:2467 [inline] __sys_sendmmsg+0x267/0x4c0 net/socket.c:2553 __do_sys_sendmmsg net/socket.c:2582 [inline] __se_sys_sendmmsg net/socket.c:2579 [inline] __x64_sys_sendmmsg+0x53/0x60 net/socket.c:2579 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x2b/0x50 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae value changed: 0x00000000 -> 0xffffff9b Reported by Kernel Concurrency Sanitizer on: CPU: 1 PID: 7670 Comm: syz-executor.3 Tainted: G W 5.18.0-rc1-syzkaller-dirty #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 I chose to not add Fixes: tag because race has minor consequences and stable teams busy enough. Signed-off-by: Eric Dumazet Reported-by: syzbot Signed-off-by: David S. Miller

ipv6: Remove __ipv6_only_sock().

2022-04-22T11:47:50+00:00

Since commit 9fe516ba3fb2 ("inet: move ipv6only in sock_common"), ipv6_only_sock() and __ipv6_only_sock() are the same macro. Let's remove the one. Signed-off-by: Kuniyuki Iwashima Reviewed-by: David Ahern Signed-off-by: David S. Miller

lsm,selinux: pass flowi_common instead of flowi to the LSM hooks

2020-11-23T23:36:21+00:00

As pointed out by Herbert in a recent related patch, the LSM hooks do not have the necessary address family information to use the flowi struct safely. As none of the LSMs currently use any of the protocol specific flowi information, replace the flowi pointers with pointers to the address family independent flowi_common struct. Reported-by: Herbert Xu Acked-by: James Morris Signed-off-by: Paul Moore

icmp6: support rfc 4884

2020-07-25T00:12:41+00:00

Extend the rfc 4884 read interface introduced for ipv4 in commit eba75c587e81 ("icmp: support rfc 4884") to ipv6. Add socket option SOL_IPV6/IPV6_RECVERR_RFC4884. Changes v1->v2: - make ipv6_icmp_error_rfc4884 static (file scope) Signed-off-by: Willem de Bruijn Signed-off-by: David S. Miller

net: ipv6: add net argument to ip6_dst_lookup_flow

2019-12-04T20:27:12+00:00

This will be used in the conversion of ipv6_stub to ip6_dst_lookup_flow, as some modules currently pass a net argument without a socket to ip6_dst_lookup. This is equivalent to commit 343d60aada5a ("ipv6: change ipv6_stub_impl.ipv6_dst_lookup to take net argument"). Signed-off-by: Sabrina Dubroca Signed-off-by: David S. Miller

udp: correct reuseport selection with connected sockets

2019-09-16T07:02:18+00:00

UDP reuseport groups can hold a mix unconnected and connected sockets. Ensure that connections only receive all traffic to their 4-tuple. Fast reuseport returns on the first reuseport match on the assumption that all matches are equal. Only if connections are present, return to the previous behavior of scoring all sockets. Record if connections are present and if so (1) treat such connected sockets as an independent match from the group, (2) only return 2-tuple matches from reuseport and (3) do not return on the first 2-tuple reuseport match to allow for a higher scoring match later. New field has_conns is set without locks. No other fields in the bitmap are modified at runtime and the field is only ever set unconditionally, so an RMW cannot miss a change. Fixes: e32ea7e74727 ("soreuseport: fast reuseport UDP socket selection") Link: http://lkml.kernel.org/r/CA+FuTSfRP09aJNYRt04SS6qj22ViiOEWaWmLAwX0psk8-PGNxw@mail.gmail.com Signed-off-by: Willem de Bruijn Acked-by: Paolo Abeni Acked-by: Craig Gallek Signed-off-by: Willem de Bruijn Signed-off-by: David S. Miller