CVE: CVE-2024-26864
Published: 2024-04-17
Description: In the Linux kernel, the following vulnerability has been resolved:

tcp: Fix refcnt handling in __inet_hash_connect().

syzbot reported a warning in sk_nulls_del_node_init_rcu().

The commit 66b60b0c8c4a ("dccp/tcp: Unhash sk from ehash for tb2 alloc
failure after check_estalblished().") tried to fix an issue that an
unconnected socket occupies an ehash entry when bhash2 allocation fails.

In such a case, we need to revert changes done by check_established(),
which does not hold refcnt when inserting socket into ehash.

So, to revert the change, we need to __sk_nulls_add_node_rcu() instead
of sk_nulls_add_node_rcu().

Otherwise, sock_put() will cause refcnt underflow and leak the socket.

[0]:
WARNING: CPU: 0 PID: 23948 at include/net/sock.h:799 sk_nulls_del_node_init_rcu+0x166/0x1a0 include/net/sock.h:799
Modules linked in:
CPU: 0 PID: 23948 Comm: syz-executor.2 Not tainted 6.8.0-rc6-syzkaller-00159-gc055fc00c07b #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
RIP: 0010:sk_nulls_del_node_init_rcu+0x166/0x1a0 include/net/sock.h:799
Code: e8 7f 71 c6 f7 83 fb 02 7c 25 e8 35 6d c6 f7 4d 85 f6 0f 95 c0 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc e8 1b 6d c6 f7 90 <0f> 0b 90 eb b2 e8 10 6d c6 f7 4c 89 e7 be 04 00 00 00 e8 63 e7 d2
RSP: 0018:ffffc900032d7848 EFLAGS: 00010246
RAX: ffffffff89cd0035 RBX: [PII_REDACTED] RCX: [PII_REDACTED]
RDX: ffffc90004de1000 RSI:[PII_REDACTED]03ffff RDI: [PII_REDACTED]
RBP: 1ffff1100439ac26 R08: ffffffff89ccffe3 R09: 1ffff1100439ac28
R10: dffffc[PII_REDACTED] R11: ffffed100439ac29 R12: ffff888021cd6140
R13: dffffc[PII_REDACTED] R14: ffff88802a9bf5c0 R15: ffff888021cd6130
FS:  00007f3b823f16c0(0000) GS:ffff8880b9400000(0000) knlGS:[PII_REDACTED]
CS:  0010 DS: 0000 ES: 0000 CR0: [PII_REDACTED]
CR2: 00007f3b823f0ff8 CR3:[PII_REDACTED]74a000 CR4:[PII_REDACTED]3506f0
DR0: [PII_REDACTED] DR1: [PII_REDACTED] DR2: [PII_REDACTED]
DR3: [PII_REDACTED] DR6: 00000000fffe0ff0 DR7: [PII_REDACTED]
Call Trace:
 <TASK>
 __inet_hash_connect+0x140f/0x20b0 net/ipv4/inet_hashtables.c:1139
 dccp_v6_connect+0xcb9/0x1480 net/dccp/ipv6.c:956
 __inet_stream_connect+0x262/0xf30 net/ipv4/af_inet.c:678
 inet_stream_connect+0x65/0xa0 net/ipv4/af_inet.c:749
 __sys_connect_file net/socket.c:2048 [inline]
 __sys_connect+0x2df/0x310 net/socket.c:2065
 __do_sys_connect net/socket.c:2075 [inline]
 __se_sys_connect net/socket.c:2072 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:2072
 do_syscall_64+0xf9/0x240
 entry_SYSCALL_64_after_hwframe+0x6f/0x77
RIP: 0033:0x7f3b8167dda9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 00 00 90 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 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f3b823f10c8 EFLAGS: 00000246 ORIG_RAX:[PII_REDACTED]00002a
RAX: ffffffffffffffda RBX: 00007f3b817abf80 RCX: 00007f3b8167dda9
RDX:[PII_REDACTED]00001c RSI: [PII_REDACTED] RDI: [PII_REDACTED]
RBP: 00007f3b823f1120 R08: [PII_REDACTED] R09: [PII_REDACTED]
R10: [PII_REDACTED] R11: [PII_REDACTED] R12: [PII_REDACTED]
R13:[PII_REDACTED]00000b R14: 00007f3b817abf80 R15: 00007ffd3beb57b8
 </TASK>
CVSS Score: 5.9 (MEDIUM)
CWE: CWE-200
References: https://git.kernel.org/stable/c/04d9d1fc428ac9f581d55118d67e0cb546701feb; https://git.kernel.org/stable/c/1b20e61d36f490319d3fbdedd410155232ab5190; https://git.kernel.org/stable/c/856baaa100cd288d3685eedae9a129c996e7e755