syzkaller reported a warning [0] in inet_csk_destroy_sock() with no
repro.

  WARN_ON(inet_sk(sk)->inet_num && !inet_csk(sk)->icsk_bind_hash);

However, the syzkaller's log hinted that connect() failed just before
the warning due to FAULT_INJECTION.  [1]

When connect() is called for an unbound socket, we search for an
available ephemeral port.  If a bhash bucket exists for the port, we
call __inet_check_established() or __inet6_check_established() to check
if the bucket is reusable.

If reusable, we add the socket into ehash and set inet_sk(sk)->inet_num.

Later, we look up the corresponding bhash2 bucket and try to allocate
it if it does not exist.

Although it rarely occurs in real use, if the allocation fails, we must
revert the changes by check_established().  Otherwise, an unconnected
socket could illegally occupy an ehash entry.

Note that we do not put tw back into ehash because sk might have
already responded to a packet for tw and it would be better to free
tw earlier under such memory presure.

[0]:
WARNING: CPU: 0 PID: 350830 at net/ipv4/inet_connection_sock.c:1193 inet_csk_destroy_sock (net/ipv4/inet_connection_sock.c:1193)
Modules linked in:
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
RIP: 0010:inet_csk_destroy_sock (net/ipv4/inet_connection_sock.c:1193)
Code: 41 5c 41 5d 41 5e e9 2d 4a 3d fd e8 28 4a 3d fd 48 89 ef e8 f0 cd 7d ff 5b 5d 41 5c 41 5d 41 5e e9 13 4a 3d fd e8 0e 4a 3d fd <0f> 0b e9 61 fe ff ff e8 02 4a 3d fd 4c 89 e7 be 03 00 00 00 e8 05
RSP: 0018:ffffc9000b21fd38 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000009e78 RCX: ffffffff840bae40
RDX: ffff88806e46c600 RSI: ffffffff840bb012 RDI: ffff88811755cca8
RBP: ffff88811755c880 R08: 0000000000000003 R09: 0000000000000000
R10: 0000000000009e78 R11: 0000000000000000 R12: ffff88811755c8e0
R13: ffff88811755c892 R14: ffff88811755c918 R15: 0000000000000000
FS:  00007f03e5243800(0000) GS:ffff88811ae00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b32f21000 CR3: 0000000112ffe001 CR4: 0000000000770ef0
PKRU: 55555554
Call Trace:
 <TASK>
 ? inet_csk_destroy_sock (net/ipv4/inet_connection_sock.c:1193)
 dccp_close (net/dccp/proto.c:1078)
 inet_release (net/ipv4/af_inet.c:434)
 __sock_release (net/socket.c:660)
 sock_close (net/socket.c:1423)
 __fput (fs/file_table.c:377)
 __fput_sync (fs/file_table.c:462)
 __x64_sys_close (fs/open.c:1557 fs/open.c:1539 fs/open.c:1539)
 do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
 entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:129)
RIP: 0033:0x7f03e53852bb
Code: 03 00 00 00 0f 05 48 3d 00 f0 ff ff 77 41 c3 48 83 ec 18 89 7c 24 0c e8 43 c9 f5 ff 8b 7c 24 0c 41 89 c0 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 35 44 89 c7 89 44 24 0c e8 a1 c9 f5 ff 8b 44
RSP: 002b:00000000005dfba0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 00007f03e53852bb
RDX: 0000000000000002 RSI: 0000000000000002 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 000000000000167c
R10: 0000000008a79680 R11: 0000000000000293 R12: 00007f03e4e43000
R13: 00007f03e4e43170 R14: 00007f03e4e43178 R15: 00007f03e4e43170
 </TASK>

[1]:
FAULT_INJECTION: forcing a failure.
name failslab, interval 1, probability 0, space 0, times 0
CPU: 0 PID: 350833 Comm: syz-executor.1 Not tainted 6.7.0-12272-g2121c43f88f5 #9
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl (lib/dump_stack.c:107 (discriminator 1))
 should_fail_ex (lib/fault-inject.c:52 lib/fault-inject.c:153)
 should_failslab (mm/slub.c:3748)
 kmem_cache_alloc (mm/slub.c:3763 mm/slub.c:3842 mm/slub.c:3867)
 inet_bind2_bucket_create (net/ipv4/inet_hashtables.c:135)
 __inet_hash_connect (net/ipv4/inet_hashtables.c:1100)
 dccp_v4_connect (net/dccp/ipv4.c:116)
 __inet_stream_connect (net/ipv4/af_inet.c:676)
 inet_stream_connect (net/ipv4/af_inet.c:747)
 __sys_connect_file (net/socket.c:2048 (discriminator 2))
 __sys_connect (net/socket.c:2065)
 __x64_sys_connect (net/socket.c:2072)
 do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
 entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:129)
RIP: 0033:0x7f03e5284e5d
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 73 9f 1b 00 f7 d8 64 89 01 48
RSP: 002b:00007f03e4641cc8 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00000000004bbf80 RCX: 00007f03e5284e5d
RDX: 0000000000000010 RSI: 0000000020000000 RDI: 0000000000000003
RBP: 00000000004bbf80 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 000000000000000b R14: 00007f03e52e5530 R15: 0000000000000000
 </TASK>

Reported-by: syzkaller <syzkaller@googlegroups.com>
Fixes: 28044fc1d495 ("net: Add a bhash2 table hashed by port and address")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Now all sockets including TIME_WAIT are linked to bhash2 using
sock_common.skc_bind_node.

We no longer use inet_bind2_bucket.deathrow, sock.sk_bind2_node,
and inet_timewait_sock.tw_bind2_node.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Now we can use sk_bind_node/tw_bind_node for bhash2, which means
we need not link TIME_WAIT sockets separately.

The dead code and sk_bind2_node will be removed in the next patch.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Now we do not use tb->owners and can unlink sockets from bhash.

sk_bind_node/tw_bind_node are available for bhash2 and will be
used in the following patch.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

We use hlist_empty(&tb->owners) to check if the bhash bucket has a socket.
We can check the child bhash2 buckets instead.

For this to work, the bhash2 bucket must be freed before the bhash bucket.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

bhash2 added a new member sk_bind2_node in struct sock to link
sockets to bhash2 in addition to bhash.

bhash is still needed to search conflicting sockets efficiently
from a port for the wildcard address.  However, bhash itself need
not have sockets.

If we link each bhash2 bucket to the corresponding bhash bucket,
we can iterate the same set of the sockets from bhash2 via bhash.

This patch links bhash2 to bhash only, and the actual use will be
in the later patches.  Finally, we will remove sk_bind2_node.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Later, we no longer link sockets to bhash.  Instead, each bhash2
bucket is linked to the corresponding bhash bucket.

Then, we pass the bhash bucket to bhash2 allocation functions as
tb.  However, tb is already used in inet_bind2_bucket_create() and
inet_bind2_bucket_init() as the bhash2 bucket.

To make the following diff clear, let's use tb2 for the bhash2 bucket
there.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

inet_bind2_bucket_addr_match() and inet_bind2_bucket_match_addr_any()
are called for each bhash2 bucket to check conflicts.  Thus, we call
ipv6_addr_any() and ipv6_addr_v4mapped() over and over during bind().

Let's avoid calling them by saving the address type in inet_bind2_bucket.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

In bhash2, IPv4/IPv6 addresses are saved in two union members,
which complicate address checks in inet_bind2_bucket_addr_match()
and inet_bind2_bucket_match_addr_any() considering uninitialised
memory and v4-mapped-v6 conflicts.

Let's simplify that by saving IPv4 address as v4-mapped-v6 address
and defining tb2.rcv_saddr as tb2.v6_rcv_saddr.s6_addr32[3].

Then, we can compare v6 address as is, and after checking v4-mapped-v6,
we can compare v4 address easily.  Also, we can remove tb2->family.

Note these functions will be further refactored in the next patch.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

The protocol family tests in inet_bind2_bucket_addr_match() and
inet_bind2_bucket_match_addr_any() are ordered as follows.

  if (sk->sk_family != tb2->family)
  else if (sk->sk_family == AF_INET6)
  else

This patch rearranges them so that AF_INET6 socket is handled first
to make the following patch tidy, where tb2->family will be removed.

  if (sk->sk_family == AF_INET6)
  else if (tb2->family == AF_INET6)
  else

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>