kernel/linux.git/net/ipv6/datagram.c, branch v6.6.134

ipv6: avoid overflows in ip6_datagram_send_ctl()

2026-04-11T12:19:24+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

inet: introduce inet->inet_flags

2023-08-16T10:09:16+00:00

Various inet fields are currently racy. do_ip_setsockopt() and do_ip_getsockopt() are mostly holding the socket lock, but some (fast) paths do not. Use a new inet->inet_flags to hold atomic bits in the series. Remove inet->cmsg_flags, and use instead 9 bits from inet_flags. Signed-off-by: Eric Dumazet Acked-by: Soheil Hassas Yeganeh Reviewed-by: Simon Horman Signed-off-by: David S. Miller

ipv6: Constify the sk parameter of several helper functions.

2023-07-14T07:27:33+00:00

icmpv6_flow_init(), ip6_datagram_flow_key_init() and ip6_mc_hdr() don't need to modify their sk argument. Make that explicit using const. Signed-off-by: Guillaume Nault Reviewed-by: Simon Horman Reviewed-by: David Ahern Signed-off-by: David S. Miller

ipv6: Fix datagram socket connection with DSCP.

2023-02-10T06:49:04+00:00

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

Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net

2022-12-13T08:49:29+00:00

Merge in the left-over fixes before the net-next pull-request. net/mptcp/subflow.c d3295fee3c75 ("mptcp: use proper req destructor for IPv6") 36b122baf6a8 ("mptcp: add subflow_v(4,6)_send_synack()") Signed-off-by: Paolo Abeni

net: setsockopt: fix IPV6_UNICAST_IF option for connected sockets

2022-12-12T10:01:58+00:00

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

net: Change the udp encap_err_rcv to allow use of {ip,ipv6}_icmp_error()

2022-11-08T16:42:28+00:00

Change the udp encap_err_rcv signature to match ip_icmp_error() and ipv6_icmp_error() so that those can be used from the called function and export them. Signed-off-by: David Howells cc: Marc Dionne cc: linux-afs@lists.infradead.org cc: netdev@vger.kernel.org

net: remove useless parameter of __sock_cmsg_send

2022-10-24T11:43:46+00:00

The parameter 'msg' has never been used by __sock_cmsg_send, so we can remove it safely. Reported-by: Zeal Robot Signed-off-by: xu xin Reviewed-by: Zhang Yunkai Acked-by: Kuniyuki Iwashima Signed-off-by: David S. Miller

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