CVE-2024-36905

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

tcp: defer shutdown(SEND_SHUTDOWN) for TCP_SYN_RECV sockets

TCP_SYN_RECV state is really special, it is only used by

cross-syn connections, mostly used by fuzzers.

In the following crash [1], syzbot managed to trigger a divide

by zero in tcp_rcv_space_adjust()

A socket makes the following state transitions,

without ever calling tcp_init_transfer(),

meaning tcp_init_buffer_space() is also not called.

TCP_CLOSE

connect()

TCP_SYN_SENT

TCP_SYN_RECV

shutdown() -> tcp_shutdown(sk, SEND_SHUTDOWN)

TCP_FIN_WAIT1

To fix this issue, change tcp_shutdown() to not

perform a TCP_SYN_RECV -> TCP_FIN_WAIT1 transition,

which makes no sense anyway.

When tcp_rcv_state_process() later changes socket state

from TCP_SYN_RECV to TCP_ESTABLISH, then look at

sk->sk_shutdown to finally enter TCP_FIN_WAIT1 state,

and send a FIN packet from a sane socket state.

This means tcp_send_fin() can now be called from BH

context, and must use GFP_ATOMIC allocations.

[1]

divide error: 0000 [#1] PREEMPT SMP KASAN NOPTI

CPU: 1 PID: 5084 Comm: syz-executor358 Not tainted 6.9.0-rc6-syzkaller-00022-g98369dccd2f8 #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024

RIP: 0010:tcp_rcv_space_adjust+0x2df/0x890 net/ipv4/tcp_input.c:767

Code: e3 04 4c 01 eb 48 8b 44 24 38 0f b6 04 10 84 c0 49 89 d5 0f 85 a5 03 00 00 41 8b 8e c8 09 00 00 89 e8 29 c8 48 0f af c3 31 d2 <48> f7 f1 48 8d 1c 43 49 8d 96 76 08 00 00 48 89 d0 48 c1 e8 03 48

RSP: 0018:ffffc900031ef3f0 EFLAGS: 00010246

RAX: 0c677a10441f8f42 RBX: 000000004fb95e7e RCX: 0000000000000000

RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000

RBP: 0000000027d4b11f R08: ffffffff89e535a4 R09: 1ffffffff25e6ab7

R10: dffffc0000000000 R11: ffffffff8135e920 R12: ffff88802a9f8d30

R13: dffffc0000000000 R14: ffff88802a9f8d00 R15: 1ffff1100553f2da

FS: 00005555775c0380(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000

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

CR2: 00007f1155bf2304 CR3: 000000002b9f2000 CR4: 0000000000350ef0

Call Trace:

<TASK>

tcp_recvmsg_locked+0x106d/0x25a0 net/ipv4/tcp.c:2513

tcp_recvmsg+0x25d/0x920 net/ipv4/tcp.c:2578

inet6_recvmsg+0x16a/0x730 net/ipv6/af_inet6.c:680

sock_recvmsg_nosec net/socket.c:1046 [inline]

sock_recvmsg+0x109/0x280 net/socket.c:1068

____sys_recvmsg+0x1db/0x470 net/socket.c:2803

___sys_recvmsg net/socket.c:2845 [inline]

do_recvmmsg+0x474/0xae0 net/socket.c:2939

__sys_recvmmsg net/socket.c:3018 [inline]

__do_sys_recvmmsg net/socket.c:3041 [inline]

__se_sys_recvmmsg net/socket.c:3034 [inline]

__x64_sys_recvmmsg+0x199/0x250 net/socket.c:3034

do_syscall_x64 arch/x86/entry/common.c:52 [inline]

do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83

entry_SYSCALL_64_after_hwframe+0x77/0x7f

RIP: 0033:0x7faeb6363db9

Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 17 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 b8 ff ff ff f7 d8 64 89 01 48

RSP: 002b:00007ffcc1997168 EFLAGS: 00000246 ORIG_RAX: 000000000000012b

RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007faeb6363db9

RDX: 0000000000000001 RSI: 0000000020000bc0 RDI: 0000000000000005

RBP: 0000000000000000 R08: 0000000000000000 R09: 000000000000001c

R10: 0000000000000122 R11: 0000000000000246 R12: 0000000000000000

R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000001