dccp/tcp: Unhash sk from ehash for tb2 alloc failure after check_estalblished().

In the Linux kernel, the following vulnerability has been resolved:

dccp/tcp: Unhash sk from ehash for tb2 alloc failure after check_estalblished().

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
---truncated---