linux.git/net/dccp/ipv4.c, branch master Linux kernel source tree net: Retire DCCP socket. 2025-04-12T01:58:10+00:00 Kuniyuki Iwashima kuniyu@amazon.com 2025-04-10T02:36:45+00:00 2a63dd0edf388802074f1d4d6b588a3b4c380688 DCCP was orphaned in 2021 by commit 054c4610bd05 ("MAINTAINERS: dccp: move Gerrit Renker to CREDITS"), which noted that the last maintainer had been inactive for five years. In recent years, it has become a playground for syzbot, and most changes to DCCP have been odd bug fixes triggered by syzbot. Apart from that, the only changes have been driven by treewide or networking API updates or adjustments related to TCP. Thus, in 2023, we announced we would remove DCCP in 2025 via commit b144fcaf46d4 ("dccp: Print deprecation notice."). Since then, only one individual has contacted the netdev mailing list. [0] There is ongoing research for Multipath DCCP. The repository is hosted on GitHub [1], and development is not taking place through the upstream community. While the repository is published under the GPLv2 license, the scheduling part remains proprietary, with a LICENSE file [2] stating: "This is not Open Source software." The researcher mentioned a plan to address the licensing issue, upstream the patches, and step up as a maintainer, but there has been no further communication since then. Maintaining DCCP for a decade without any real users has become a burden. Therefore, it's time to remove it. Removing DCCP will also provide significant benefits to TCP. It allows us to freely reorganize the layout of struct inet_connection_sock, which is currently shared with DCCP, and optimize it to reduce the number of cachelines accessed in the TCP fast path. Note that we keep DCCP netfilter modules as requested. [3] Link: https://lore.kernel.org/netdev/20230710182253.81446-1-kuniyu@amazon.com/T/#u #[0] Link: https://github.com/telekom/mp-dccp #[1] Link: https://github.com/telekom/mp-dccp/blob/mpdccp_v03_k5.10/net/dccp/non_gpl_scheduler/LICENSE #[2] Link: https://lore.kernel.org/netdev/Z_VQ0KlCRkqYWXa-@calendula/ #[3] Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com> Acked-by: Paul Moore <paul@paul-moore.com> (LSM and SELinux) Acked-by: Casey Schaufler <casey@schaufler-ca.com> Link: https://patch.msgid.link/20250410023921.11307-3-kuniyu@amazon.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
DCCP was orphaned in 2021 by commit 054c4610bd05 ("MAINTAINERS: dccp:
move Gerrit Renker to CREDITS"), which noted that the last maintainer
had been inactive for five years.

In recent years, it has become a playground for syzbot, and most changes
to DCCP have been odd bug fixes triggered by syzbot.  Apart from that,
the only changes have been driven by treewide or networking API updates
or adjustments related to TCP.

Thus, in 2023, we announced we would remove DCCP in 2025 via commit
b144fcaf46d4 ("dccp: Print deprecation notice.").

Since then, only one individual has contacted the netdev mailing list. [0]

There is ongoing research for Multipath DCCP.  The repository is hosted
on GitHub [1], and development is not taking place through the upstream
community.  While the repository is published under the GPLv2 license,
the scheduling part remains proprietary, with a LICENSE file [2] stating:

  "This is not Open Source software."

The researcher mentioned a plan to address the licensing issue, upstream
the patches, and step up as a maintainer, but there has been no further
communication since then.

Maintaining DCCP for a decade without any real users has become a burden.

Therefore, it's time to remove it.

Removing DCCP will also provide significant benefits to TCP.  It allows
us to freely reorganize the layout of struct inet_connection_sock, which
is currently shared with DCCP, and optimize it to reduce the number of
cachelines accessed in the TCP fast path.

Note that we keep DCCP netfilter modules as requested.  [3]

Link: https://lore.kernel.org/netdev/20230710182253.81446-1-kuniyu@amazon.com/T/#u #[0]
Link: https://github.com/telekom/mp-dccp #[1]
Link: https://github.com/telekom/mp-dccp/blob/mpdccp_v03_k5.10/net/dccp/non_gpl_scheduler/LICENSE #[2]
Link: https://lore.kernel.org/netdev/Z_VQ0KlCRkqYWXa-@calendula/ #[3]
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Acked-by: Paul Moore <paul@paul-moore.com> (LSM and SELinux)
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Link: https://patch.msgid.link/20250410023921.11307-3-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
tcp/dccp: Remove inet_connection_sock_af_ops.addr2sockaddr(). 2025-03-24T19:10:13+00:00 Kuniyuki Iwashima kuniyu@amazon.com 2025-03-18T06:01:07+00:00 66034f78a5583bc10c195647629a137e8ed02208 inet_connection_sock_af_ops.addr2sockaddr() hasn't been used at all in the git era. $ git grep addr2sockaddr $(git rev-list HEAD | tail -n 1) Let's remove it. Note that there was a 4 bytes hole after sockaddr_len and now it's 6 bytes, so the binary layout is not changed. Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20250318060112.3729-1-kuniyu@amazon.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
inet_connection_sock_af_ops.addr2sockaddr() hasn't been used at all
in the git era.

  $ git grep addr2sockaddr $(git rev-list HEAD | tail -n 1)

Let's remove it.

Note that there was a 4 bytes hole after sockaddr_len and now it's
6 bytes, so the binary layout is not changed.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250318060112.3729-1-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
inet: consolidate inet_csk_clone_lock() 2025-02-14T21:40:33+00:00 Eric Dumazet edumazet@google.com 2025-02-12T13:13:28+00:00 a3a128f611a965fddf8a02dd45716f96e0738e00 Current inet_sock_set_state trace from inet_csk_clone_lock() is missing many details : ... sock:inet_sock_set_state: family=AF_INET6 protocol=IPPROTO_TCP \ sport=4901 dport=0 \ saddr=127.0.0.6 daddr=0.0.0.0 \ saddrv6=:: daddrv6=:: \ oldstate=TCP_LISTEN newstate=TCP_SYN_RECV Only the sport gives the listener port, no other parts of the n-tuple are correct. In this patch, I initialize relevant fields of the new socket before calling inet_sk_set_state(newsk, TCP_SYN_RECV). We now have a trace including all the source/destination bits. ... sock:inet_sock_set_state: family=AF_INET6 protocol=IPPROTO_TCP \ sport=4901 dport=47648 \ saddr=127.0.0.6 daddr=127.0.0.6 \ saddrv6=2002:a05:6830:1f85:: daddrv6=2001:4860:f803:65::3 \ oldstate=TCP_LISTEN newstate=TCP_SYN_RECV Signed-off-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com> Link: https://patch.msgid.link/20250212131328.1514243-3-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
Current inet_sock_set_state trace from inet_csk_clone_lock() is missing
many details :

... sock:inet_sock_set_state: family=AF_INET6 protocol=IPPROTO_TCP \
    sport=4901 dport=0 \
    saddr=127.0.0.6 daddr=0.0.0.0 \
    saddrv6=:: daddrv6=:: \
    oldstate=TCP_LISTEN newstate=TCP_SYN_RECV

Only the sport gives the listener port, no other parts of the n-tuple are correct.

In this patch, I initialize relevant fields of the new socket before
calling inet_sk_set_state(newsk, TCP_SYN_RECV).

We now have a trace including all the source/destination bits.

... sock:inet_sock_set_state: family=AF_INET6 protocol=IPPROTO_TCP \
    sport=4901 dport=47648 \
    saddr=127.0.0.6 daddr=127.0.0.6 \
    saddrv6=2002:a05:6830:1f85:: daddrv6=2001:4860:f803:65::3 \
    oldstate=TCP_LISTEN newstate=TCP_SYN_RECV

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250212131328.1514243-3-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
dccp: Prepare dccp_v4_route_skb() to .flowi4_tos conversion. 2025-01-18T03:01:21+00:00 Guillaume Nault gnault@redhat.com 2025-01-16T13:10:16+00:00 02673d58adfa51e5e326d7472f251a63f42fcd93 Use inet_sk_dscp() to get the socket DSCP value as dscp_t, instead of ip_sock_rt_tos() which returns a __u8. This will ease the conversion of fl4->flowi4_tos to dscp_t, which now just becomes a matter of dropping the inet_dscp_to_dsfield() call. Signed-off-by: Guillaume Nault <gnault@redhat.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Ido Schimmel <idosch@nvidia.com> Link: https://patch.msgid.link/208dc5ca28bb5595d7a545de026bba18b1d63bda.1737032802.git.gnault@redhat.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
Use inet_sk_dscp() to get the socket DSCP value as dscp_t, instead of
ip_sock_rt_tos() which returns a __u8. This will ease the conversion
of fl4->flowi4_tos to dscp_t, which now just becomes a matter of
dropping the inet_dscp_to_dsfield() call.

Signed-off-by: Guillaume Nault <gnault@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/208dc5ca28bb5595d7a545de026bba18b1d63bda.1737032802.git.gnault@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Fix race for duplicate reqsk on identical SYN 2024-06-25T09:37:45+00:00 luoxuanqiang luoxuanqiang@kylinos.cn 2024-06-21T01:39:29+00:00 ff46e3b4421923937b7f6e44ffcd3549a074f321 When bonding is configured in BOND_MODE_BROADCAST mode, if two identical SYN packets are received at the same time and processed on different CPUs, it can potentially create the same sk (sock) but two different reqsk (request_sock) in tcp_conn_request(). These two different reqsk will respond with two SYNACK packets, and since the generation of the seq (ISN) incorporates a timestamp, the final two SYNACK packets will have different seq values. The consequence is that when the Client receives and replies with an ACK to the earlier SYNACK packet, we will reset(RST) it. ======================================================================== This behavior is consistently reproducible in my local setup, which comprises: | NETA1 ------ NETB1 | PC_A --- bond --- | | --- bond --- PC_B | NETA2 ------ NETB2 | - PC_A is the Server and has two network cards, NETA1 and NETA2. I have bonded these two cards using BOND_MODE_BROADCAST mode and configured them to be handled by different CPU. - PC_B is the Client, also equipped with two network cards, NETB1 and NETB2, which are also bonded and configured in BOND_MODE_BROADCAST mode. If the client attempts a TCP connection to the server, it might encounter a failure. Capturing packets from the server side reveals: 10.10.10.10.45182 > localhost: Flags [S], seq 320236027, 10.10.10.10.45182 > localhost: Flags [S], seq 320236027, localhost > 10.10.10.10.45182: Flags [S.], seq 2967855116, localhost > 10.10.10.10.45182: Flags [S.], seq 2967855123, <== 10.10.10.10.45182 > localhost: Flags [.], ack 4294967290, 10.10.10.10.45182 > localhost: Flags [.], ack 4294967290, localhost > 10.10.10.10.45182: Flags [R], seq 2967855117, <== localhost > 10.10.10.10.45182: Flags [R], seq 2967855117, Two SYNACKs with different seq numbers are sent by localhost, resulting in an anomaly. ======================================================================== The attempted solution is as follows: Add a return value to inet_csk_reqsk_queue_hash_add() to confirm if the ehash insertion is successful (Up to now, the reason for unsuccessful insertion is that a reqsk for the same connection has already been inserted). If the insertion fails, release the reqsk. Due to the refcnt, Kuniyuki suggests also adding a return value check for the DCCP module; if ehash insertion fails, indicating a successful insertion of the same connection, simply release the reqsk as well. Simultaneously, In the reqsk_queue_hash_req(), the start of the req->rsk_timer is adjusted to be after successful insertion. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: luoxuanqiang <luoxuanqiang@kylinos.cn> Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Link: https://lore.kernel.org/r/20240621013929.1386815-1-luoxuanqiang@kylinos.cn Signed-off-by: Paolo Abeni <pabeni@redhat.com> 
When bonding is configured in BOND_MODE_BROADCAST mode, if two identical
SYN packets are received at the same time and processed on different CPUs,
it can potentially create the same sk (sock) but two different reqsk
(request_sock) in tcp_conn_request().

These two different reqsk will respond with two SYNACK packets, and since
the generation of the seq (ISN) incorporates a timestamp, the final two
SYNACK packets will have different seq values.

The consequence is that when the Client receives and replies with an ACK
to the earlier SYNACK packet, we will reset(RST) it.

========================================================================

This behavior is consistently reproducible in my local setup,
which comprises:

                  | NETA1 ------ NETB1 |
PC_A --- bond --- |                    | --- bond --- PC_B
                  | NETA2 ------ NETB2 |

- PC_A is the Server and has two network cards, NETA1 and NETA2. I have
  bonded these two cards using BOND_MODE_BROADCAST mode and configured
  them to be handled by different CPU.

- PC_B is the Client, also equipped with two network cards, NETB1 and
  NETB2, which are also bonded and configured in BOND_MODE_BROADCAST mode.

If the client attempts a TCP connection to the server, it might encounter
a failure. Capturing packets from the server side reveals:

10.10.10.10.45182 > localhost: Flags [S], seq 320236027,
10.10.10.10.45182 > localhost: Flags [S], seq 320236027,
localhost > 10.10.10.10.45182: Flags [S.], seq 2967855116,
localhost > 10.10.10.10.45182: Flags [S.], seq 2967855123, <==
10.10.10.10.45182 > localhost: Flags [.], ack 4294967290,
10.10.10.10.45182 > localhost: Flags [.], ack 4294967290,
localhost > 10.10.10.10.45182: Flags [R], seq 2967855117, <==
localhost > 10.10.10.10.45182: Flags [R], seq 2967855117,

Two SYNACKs with different seq numbers are sent by localhost,
resulting in an anomaly.

========================================================================

The attempted solution is as follows:
Add a return value to inet_csk_reqsk_queue_hash_add() to confirm if the
ehash insertion is successful (Up to now, the reason for unsuccessful
insertion is that a reqsk for the same connection has already been
inserted). If the insertion fails, release the reqsk.

Due to the refcnt, Kuniyuki suggests also adding a return value check
for the DCCP module; if ehash insertion fails, indicating a successful
insertion of the same connection, simply release the reqsk as well.

Simultaneously, In the reqsk_queue_hash_req(), the start of the
req->rsk_timer is adjusted to be after successful insertion.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: luoxuanqiang <luoxuanqiang@kylinos.cn>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20240621013929.1386815-1-luoxuanqiang@kylinos.cn
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
rstreason: prepare for passive reset 2024-04-26T13:34:00+00:00 Jason Xing kernelxing@tencent.com 2024-04-25T03:13:35+00:00 6be49deaa09576c141002a2e6f816a1709bc2c86 Adjust the parameter and support passing reason of reset which is for now NOT_SPECIFIED. No functional changes. Signed-off-by: Jason Xing <kernelxing@tencent.com> Acked-by: Matthieu Baerts (NGI0) <matttbe@kernel.org> Reviewed-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Paolo Abeni <pabeni@redhat.com> 
Adjust the parameter and support passing reason of reset which
is for now NOT_SPECIFIED. No functional changes.

Signed-off-by: Jason Xing <kernelxing@tencent.com>
Acked-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
tcp/dccp: do not care about families in inet_twsk_purge() 2024-04-02T04:27:58+00:00 Eric Dumazet edumazet@google.com 2024-03-29T15:32:03+00:00 1eeb5043573981f3a1278876515851b7f6b1df1b We lost ability to unload ipv6 module a long time ago. Instead of calling expensive inet_twsk_purge() twice, we can handle all families in one round. Also remove an extra line added in my prior patch, per Kuniyuki Iwashima feedback. Signed-off-by: Eric Dumazet <edumazet@google.com> Link: https://lore.kernel.org/netdev/20240327192934.6843-1-kuniyu@amazon.com/ Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com> Link: https://lore.kernel.org/r/20240329153203.345203-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> 
We lost ability to unload ipv6 module a long time ago.

Instead of calling expensive inet_twsk_purge() twice,
we can handle all families in one round.

Also remove an extra line added in my prior patch,
per Kuniyuki Iwashima feedback.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/netdev/20240327192934.6843-1-kuniyu@amazon.com/
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20240329153203.345203-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
dccp: Call security_inet_conn_request() after setting IPv4 addresses. 2023-11-02T11:55:42+00:00 Kuniyuki Iwashima kuniyu@amazon.com 2023-10-30T20:10:41+00:00 fa2df45af13091f76b89adb84a28f13818d5d631 Initially, commit 4237c75c0a35 ("[MLSXFRM]: Auto-labeling of child sockets") introduced security_inet_conn_request() in some functions where reqsk is allocated. The hook is added just after the allocation, so reqsk's IPv4 remote address was not initialised then. However, SELinux/Smack started to read it in netlbl_req_setattr() after the cited commits. This bug was partially fixed by commit 284904aa7946 ("lsm: Relocate the IPv4 security_inet_conn_request() hooks"). This patch fixes the last bug in DCCPv4. Fixes: 389fb800ac8b ("netlabel: Label incoming TCP connections correctly in SELinux") Fixes: 07feee8f812f ("netlabel: Cleanup the Smack/NetLabel code to fix incoming TCP connections") Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com> Acked-by: Paul Moore <paul@paul-moore.com> Signed-off-by: Paolo Abeni <pabeni@redhat.com> 
Initially, commit 4237c75c0a35 ("[MLSXFRM]: Auto-labeling of child
sockets") introduced security_inet_conn_request() in some functions
where reqsk is allocated.  The hook is added just after the allocation,
so reqsk's IPv4 remote address was not initialised then.

However, SELinux/Smack started to read it in netlbl_req_setattr()
after the cited commits.

This bug was partially fixed by commit 284904aa7946 ("lsm: Relocate
the IPv4 security_inet_conn_request() hooks").

This patch fixes the last bug in DCCPv4.

Fixes: 389fb800ac8b ("netlabel: Label incoming TCP connections correctly in SELinux")
Fixes: 07feee8f812f ("netlabel: Cleanup the Smack/NetLabel code to fix incoming TCP connections")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Acked-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
inet: implement lockless IP_TOS 2023-10-01T18:39:18+00:00 Eric Dumazet edumazet@google.com 2023-09-22T03:42:16+00:00 e08d0b3d172311e2bb500865c0d0038533d0ff11 Some reads of inet->tos are racy. Add needed READ_ONCE() annotations and convert IP_TOS option lockless. v2: missing changes in include/net/route.h (David Ahern) Signed-off-by: Eric Dumazet <edumazet@google.com> Reviewed-by: David Ahern <dsahern@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net> 
Some reads of inet->tos are racy.

Add needed READ_ONCE() annotations and convert IP_TOS option lockless.

v2: missing changes in include/net/route.h (David Ahern)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
dccp: fix dccp_v4_err()/dccp_v6_err() again 2023-09-18T06:10:31+00:00 Eric Dumazet edumazet@google.com 2023-09-15T19:00:35+00:00 6af289746a636f71f4c0535a9801774118486c7a dh->dccph_x is the 9th byte (offset 8) in "struct dccp_hdr", not in the "byte 7" as Jann claimed. We need to make sure the ICMP messages are big enough, using more standard ways (no more assumptions). syzbot reported: BUG: KMSAN: uninit-value in pskb_may_pull_reason include/linux/skbuff.h:2667 [inline] BUG: KMSAN: uninit-value in pskb_may_pull include/linux/skbuff.h:2681 [inline] BUG: KMSAN: uninit-value in dccp_v6_err+0x426/0x1aa0 net/dccp/ipv6.c:94 pskb_may_pull_reason include/linux/skbuff.h:2667 [inline] pskb_may_pull include/linux/skbuff.h:2681 [inline] dccp_v6_err+0x426/0x1aa0 net/dccp/ipv6.c:94 icmpv6_notify+0x4c7/0x880 net/ipv6/icmp.c:867 icmpv6_rcv+0x19d5/0x30d0 ip6_protocol_deliver_rcu+0xda6/0x2a60 net/ipv6/ip6_input.c:438 ip6_input_finish net/ipv6/ip6_input.c:483 [inline] NF_HOOK include/linux/netfilter.h:304 [inline] ip6_input+0x15d/0x430 net/ipv6/ip6_input.c:492 ip6_mc_input+0xa7e/0xc80 net/ipv6/ip6_input.c:586 dst_input include/net/dst.h:468 [inline] ip6_rcv_finish+0x5db/0x870 net/ipv6/ip6_input.c:79 NF_HOOK include/linux/netfilter.h:304 [inline] ipv6_rcv+0xda/0x390 net/ipv6/ip6_input.c:310 __netif_receive_skb_one_core net/core/dev.c:5523 [inline] __netif_receive_skb+0x1a6/0x5a0 net/core/dev.c:5637 netif_receive_skb_internal net/core/dev.c:5723 [inline] netif_receive_skb+0x58/0x660 net/core/dev.c:5782 tun_rx_batched+0x83b/0x920 tun_get_user+0x564c/0x6940 drivers/net/tun.c:2002 tun_chr_write_iter+0x3af/0x5d0 drivers/net/tun.c:2048 call_write_iter include/linux/fs.h:1985 [inline] new_sync_write fs/read_write.c:491 [inline] vfs_write+0x8ef/0x15c0 fs/read_write.c:584 ksys_write+0x20f/0x4c0 fs/read_write.c:637 __do_sys_write fs/read_write.c:649 [inline] __se_sys_write fs/read_write.c:646 [inline] __x64_sys_write+0x93/0xd0 fs/read_write.c:646 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd Uninit was created at: slab_post_alloc_hook+0x12f/0xb70 mm/slab.h:767 slab_alloc_node mm/slub.c:3478 [inline] kmem_cache_alloc_node+0x577/0xa80 mm/slub.c:3523 kmalloc_reserve+0x13d/0x4a0 net/core/skbuff.c:559 __alloc_skb+0x318/0x740 net/core/skbuff.c:650 alloc_skb include/linux/skbuff.h:1286 [inline] alloc_skb_with_frags+0xc8/0xbd0 net/core/skbuff.c:6313 sock_alloc_send_pskb+0xa80/0xbf0 net/core/sock.c:2795 tun_alloc_skb drivers/net/tun.c:1531 [inline] tun_get_user+0x23cf/0x6940 drivers/net/tun.c:1846 tun_chr_write_iter+0x3af/0x5d0 drivers/net/tun.c:2048 call_write_iter include/linux/fs.h:1985 [inline] new_sync_write fs/read_write.c:491 [inline] vfs_write+0x8ef/0x15c0 fs/read_write.c:584 ksys_write+0x20f/0x4c0 fs/read_write.c:637 __do_sys_write fs/read_write.c:649 [inline] __se_sys_write fs/read_write.c:646 [inline] __x64_sys_write+0x93/0xd0 fs/read_write.c:646 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd CPU: 0 PID: 4995 Comm: syz-executor153 Not tainted 6.6.0-rc1-syzkaller-00014-ga747acc0b752 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/04/2023 Fixes: 977ad86c2a1b ("dccp: Fix out of bounds access in DCCP error handler") Reported-by: syzbot <syzkaller@googlegroups.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Jann Horn <jannh@google.com> Reviewed-by: Jann Horn <jannh@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> 
dh->dccph_x is the 9th byte (offset 8) in "struct dccp_hdr",
not in the "byte 7" as Jann claimed.

We need to make sure the ICMP messages are big enough,
using more standard ways (no more assumptions).

syzbot reported:
BUG: KMSAN: uninit-value in pskb_may_pull_reason include/linux/skbuff.h:2667 [inline]
BUG: KMSAN: uninit-value in pskb_may_pull include/linux/skbuff.h:2681 [inline]
BUG: KMSAN: uninit-value in dccp_v6_err+0x426/0x1aa0 net/dccp/ipv6.c:94
pskb_may_pull_reason include/linux/skbuff.h:2667 [inline]
pskb_may_pull include/linux/skbuff.h:2681 [inline]
dccp_v6_err+0x426/0x1aa0 net/dccp/ipv6.c:94
icmpv6_notify+0x4c7/0x880 net/ipv6/icmp.c:867
icmpv6_rcv+0x19d5/0x30d0
ip6_protocol_deliver_rcu+0xda6/0x2a60 net/ipv6/ip6_input.c:438
ip6_input_finish net/ipv6/ip6_input.c:483 [inline]
NF_HOOK include/linux/netfilter.h:304 [inline]
ip6_input+0x15d/0x430 net/ipv6/ip6_input.c:492
ip6_mc_input+0xa7e/0xc80 net/ipv6/ip6_input.c:586
dst_input include/net/dst.h:468 [inline]
ip6_rcv_finish+0x5db/0x870 net/ipv6/ip6_input.c:79
NF_HOOK include/linux/netfilter.h:304 [inline]
ipv6_rcv+0xda/0x390 net/ipv6/ip6_input.c:310
__netif_receive_skb_one_core net/core/dev.c:5523 [inline]
__netif_receive_skb+0x1a6/0x5a0 net/core/dev.c:5637
netif_receive_skb_internal net/core/dev.c:5723 [inline]
netif_receive_skb+0x58/0x660 net/core/dev.c:5782
tun_rx_batched+0x83b/0x920
tun_get_user+0x564c/0x6940 drivers/net/tun.c:2002
tun_chr_write_iter+0x3af/0x5d0 drivers/net/tun.c:2048
call_write_iter include/linux/fs.h:1985 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x8ef/0x15c0 fs/read_write.c:584
ksys_write+0x20f/0x4c0 fs/read_write.c:637
__do_sys_write fs/read_write.c:649 [inline]
__se_sys_write fs/read_write.c:646 [inline]
__x64_sys_write+0x93/0xd0 fs/read_write.c:646
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

Uninit was created at:
slab_post_alloc_hook+0x12f/0xb70 mm/slab.h:767
slab_alloc_node mm/slub.c:3478 [inline]
kmem_cache_alloc_node+0x577/0xa80 mm/slub.c:3523
kmalloc_reserve+0x13d/0x4a0 net/core/skbuff.c:559
__alloc_skb+0x318/0x740 net/core/skbuff.c:650
alloc_skb include/linux/skbuff.h:1286 [inline]
alloc_skb_with_frags+0xc8/0xbd0 net/core/skbuff.c:6313
sock_alloc_send_pskb+0xa80/0xbf0 net/core/sock.c:2795
tun_alloc_skb drivers/net/tun.c:1531 [inline]
tun_get_user+0x23cf/0x6940 drivers/net/tun.c:1846
tun_chr_write_iter+0x3af/0x5d0 drivers/net/tun.c:2048
call_write_iter include/linux/fs.h:1985 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x8ef/0x15c0 fs/read_write.c:584
ksys_write+0x20f/0x4c0 fs/read_write.c:637
__do_sys_write fs/read_write.c:649 [inline]
__se_sys_write fs/read_write.c:646 [inline]
__x64_sys_write+0x93/0xd0 fs/read_write.c:646
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

CPU: 0 PID: 4995 Comm: syz-executor153 Not tainted 6.6.0-rc1-syzkaller-00014-ga747acc0b752 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/04/2023

Fixes: 977ad86c2a1b ("dccp: Fix out of bounds access in DCCP error handler")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jann Horn <jannh@google.com>
Reviewed-by: Jann Horn <jannh@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>