CVE-2024-36904

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

tcp: Use refcount_inc_not_zero() in tcp_twsk_unique().

Anderson Nascimento reported a use-after-free splat in tcp_twsk_unique()

with nice analysis.

Since commit ec94c2696f0b ("tcp/dccp: avoid one atomic operation for

timewait hashdance"), inet_twsk_hashdance() sets TIME-WAIT socket's

sk_refcnt after putting it into ehash and releasing the bucket lock.

Thus, there is a small race window where other threads could try to

reuse the port during connect() and call sock_hold() in tcp_twsk_unique()

for the TIME-WAIT socket with zero refcnt.

If that happens, the refcnt taken by tcp_twsk_unique() is overwritten

and sock_put() will cause underflow, triggering a real use-after-free

somewhere else.

To avoid the use-after-free, we need to use refcount_inc_not_zero() in

tcp_twsk_unique() and give up on reusing the port if it returns false.

[0]:

refcount_t: addition on 0; use-after-free.

WARNING: CPU: 0 PID: 1039313 at lib/refcount.c:25 refcount_warn_saturate+0xe5/0x110

CPU: 0 PID: 1039313 Comm: trigger Not tainted 6.8.6-200.fc39.x86_64 #1

Hardware name: VMware, Inc. VMware20,1/440BX Desktop Reference Platform, BIOS VMW201.00V.21805430.B64.2305221830 05/22/2023

RIP: 0010:refcount_warn_saturate+0xe5/0x110

Code: 42 8e ff 0f 0b c3 cc cc cc cc 80 3d aa 13 ea 01 00 0f 85 5e ff ff ff 48 c7 c7 f8 8e b7 82 c6 05 96 13 ea 01 01 e8 7b 42 8e ff <0f> 0b c3 cc cc cc cc 48 c7 c7 50 8f b7 82 c6 05 7a 13 ea 01 01 e8

RSP: 0018:ffffc90006b43b60 EFLAGS: 00010282

RAX: 0000000000000000 RBX: ffff888009bb3ef0 RCX: 0000000000000027

RDX: ffff88807be218c8 RSI: 0000000000000001 RDI: ffff88807be218c0

RBP: 0000000000069d70 R08: 0000000000000000 R09: ffffc90006b439f0

R10: ffffc90006b439e8 R11: 0000000000000003 R12: ffff8880029ede84

R13: 0000000000004e20 R14: ffffffff84356dc0 R15: ffff888009bb3ef0

FS: 00007f62c10926c0(0000) GS:ffff88807be00000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 0000000020ccb000 CR3: 000000004628c005 CR4: 0000000000f70ef0

PKRU: 55555554

Call Trace:

<TASK>

? refcount_warn_saturate+0xe5/0x110

? __warn+0x81/0x130

? refcount_warn_saturate+0xe5/0x110

? report_bug+0x171/0x1a0

? refcount_warn_saturate+0xe5/0x110

? handle_bug+0x3c/0x80

? exc_invalid_op+0x17/0x70

? asm_exc_invalid_op+0x1a/0x20

? refcount_warn_saturate+0xe5/0x110

tcp_twsk_unique+0x186/0x190

__inet_check_established+0x176/0x2d0

__inet_hash_connect+0x74/0x7d0

? __pfx___inet_check_established+0x10/0x10

tcp_v4_connect+0x278/0x530

__inet_stream_connect+0x10f/0x3d0

inet_stream_connect+0x3a/0x60

__sys_connect+0xa8/0xd0

__x64_sys_connect+0x18/0x20

do_syscall_64+0x83/0x170

entry_SYSCALL_64_after_hwframe+0x78/0x80

RIP: 0033:0x7f62c11a885d

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 a3 45 0c 00 f7 d8 64 89 01 48

RSP: 002b:00007f62c1091e58 EFLAGS: 00000296 ORIG_RAX: 000000000000002a

RAX: ffffffffffffffda RBX: 0000000020ccb004 RCX: 00007f62c11a885d

RDX: 0000000000000010 RSI: 0000000020ccb000 RDI: 0000000000000003

RBP: 00007f62c1091e90 R08: 0000000000000000 R09: 0000000000000000

R10: 0000000000000000 R11: 0000000000000296 R12: 00007f62c10926c0

R13: ffffffffffffff88 R14: 0000000000000000 R15: 00007ffe237885b0

</TASK>