[PATCH 5.10.y] bpf, sockmap: Fix an infinite loop error when len is 0 in tcp_bpf_recvmsg_parser()

[PATCH 5.10.y] bpf, sockmap: Fix an infinite loop error when len is 0 in tcp_bpf_recvmsg_parser()

[Vasiliy Kovalev]

From: Liu Jian <liujian56@huawei.com>

commit d900f3d20cc3169ce42ec72acc850e662a4d4db2 upstream.

When the buffer length of the recvmsg system call is 0, we got the
flollowing soft lockup problem:

watchdog: BUG: soft lockup - CPU#3 stuck for 27s! [a.out:6149]
CPU: 3 PID: 6149 Comm: a.out Kdump: loaded Not tainted 6.2.0+ #30
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01/2014
RIP: 0010:remove_wait_queue+0xb/0xc0
Code: 5e 41 5f c3 cc cc cc cc 0f 1f 80 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 41 57 <41> 56 41 55 41 54 55 48 89 fd 53 48 89 f3 4c 8d 6b 18 4c 8d 73 20
RSP: 0018:ffff88811b5978b8 EFLAGS: 00000246
RAX: 0000000000000000 RBX: ffff88811a7d3780 RCX: ffffffffb7a4d768
RDX: dffffc0000000000 RSI: ffff88811b597908 RDI: ffff888115408040
RBP: 1ffff110236b2f1b R08: 0000000000000000 R09: ffff88811a7d37e7
R10: ffffed10234fa6fc R11: 0000000000000001 R12: ffff88811179b800
R13: 0000000000000001 R14: ffff88811a7d38a8 R15: ffff88811a7d37e0
FS:  00007f6fb5398740(0000) GS:ffff888237180000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000000 CR3: 000000010b6ba002 CR4: 0000000000370ee0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 tcp_msg_wait_data+0x279/0x2f0
 tcp_bpf_recvmsg_parser+0x3c6/0x490
 inet_recvmsg+0x280/0x290
 sock_recvmsg+0xfc/0x120
 ____sys_recvmsg+0x160/0x3d0
 ___sys_recvmsg+0xf0/0x180
 __sys_recvmsg+0xea/0x1a0
 do_syscall_64+0x3f/0x90
 entry_SYSCALL_64_after_hwframe+0x72/0xdc

The logic in tcp_bpf_recvmsg_parser is as follows:

msg_bytes_ready:
	copied = sk_msg_recvmsg(sk, psock, msg, len, flags);
	if (!copied) {
		wait data;
		goto msg_bytes_ready;
	}

In this case, "copied" always is 0, the infinite loop occurs.

According to the Linux system call man page, 0 should be returned in this
case. Therefore, in tcp_bpf_recvmsg_parser(), if the length is 0, directly
return. Also modify several other functions with the same problem.

Fixes: 1f5be6b3b063 ("udp: Implement udp_bpf_recvmsg() for sockmap")
Fixes: 9825d866ce0d ("af_unix: Implement unix_dgram_bpf_recvmsg()")
Fixes: c5d2177a72a1 ("bpf, sockmap: Fix race in ingress receive verdict with redirect to self")
Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: Liu Jian <liujian56@huawei.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Cc: Jakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/20230303080946.1146638-1-liujian56@huawei.com
[ kovalev: bp to fix CVE-2023-53133; applied only to tcp_bpf_recvmsg as the
  older kernel lacks tcp_bpf_recvmsg_parser, udp_bpf_recvmsg and
  unix_bpf_recvmsg (see upstream commits c5d2177a72a1, 1f5be6b3b063 and
  9825d866ce0d) ]
Signed-off-by: Vasiliy Kovalev <kovalev@altlinux.org>
---
 net/ipv4/tcp_bpf.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
index bcd5fc484f77..76cd97488777 100644
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -277,6 +277,9 @@ static int tcp_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 	if (unlikely(flags & MSG_ERRQUEUE))
 		return inet_recv_error(sk, msg, len, addr_len);
 
+	if (!len)
+		return 0;
+
 	psock = sk_psock_get(sk);
 	if (unlikely(!psock))
 		return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len);
-- 
2.50.1

Re: [PATCH 5.10.y] bpf, sockmap: Fix an infinite loop error when len is 0 in tcp_bpf_recvmsg_parser()

[sashiko-bot]

Sashiko AI review found 1 potential issue(s):
- [High] Unconditional early return for `len == 0` in `tcp_bpf_recvmsg()` breaks UAPI semantics by masking socket errors, returning 0 instead of `-EAGAIN` for non-blocking sockets, and bypassing state checks.
--

commit 17cc1ee5a157715faa482ac2a4f167f9022cb333
Author: Liu Jian <liujian56@huawei.com>

bpf, sockmap: Fix an infinite loop error when len is 0 in tcp_bpf_recvmsg_parser()

This commit addresses a soft lockup issue where a 0-length recvmsg causes
an infinite loop in tcp_bpf_recvmsg_parser(). It fixes the issue by returning
0 early when the length is 0.

Link: https://lore.kernel.org/bpf/20230303080946.1146638-1-liujian56@huawei.com

> --- a/net/ipv4/tcp_bpf.c
> +++ b/net/ipv4/tcp_bpf.c
> @@ -277,6 +277,9 @@ static int tcp_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
>  	if (unlikely(flags & MSG_ERRQUEUE))
>  		return inet_recv_error(sk, msg, len, addr_len);
>  
> +	if (!len)
> +		return 0;

Does this unconditional early return bypass necessary socket state checks?

In the standard Linux TCP implementation, a 0-length receive is not an
immediate no-op. For instance, if the socket is non-blocking and empty,
tcp_recvmsg() normally returns -EAGAIN. If the socket has a pending error,
it returns that error, and if the socket is in TCP_LISTEN, it returns
-ENOTCONN.

By unconditionally returning 0 here, a non-blocking recv(0) on an empty
socket will return 0 instead of -EAGAIN. Since a 0 return value typically
indicates EOF (connection closed) to userspace applications, could this
cause applications to incorrectly assume the connection was closed and
drop it?

Would it be safer to delegate 0-length reads to the standard TCP
implementation by returning tcp_recvmsg() here instead, ensuring that
the existing UAPI error semantics are preserved?

> +
>  	psock = sk_psock_get(sk);
>  	if (unlikely(!psock))
>  		return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260421132839.38703-1-kovalev@altlinux.org?part=1