6.6-stable review patch. If anyone has any objections, please let me know.
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From: Zijian Zhang zijianzhang@bytedance.com
[ Upstream commit ca70b8baf2bd125b2a4d96e76db79375c07d7ff2 ]
The current sk memory accounting logic in __SK_REDIRECT is pre-uncharging tosend bytes, which is either msg->sg.size or a smaller value apply_bytes.
Potential problems with this strategy are as follows:
- If the actual sent bytes are smaller than tosend, we need to charge some bytes back, as in line 487, which is okay but seems not clean.
- When tosend is set to apply_bytes, as in line 417, and (ret < 0), we may miss uncharging (msg->sg.size - apply_bytes) bytes.
[...] 415 tosend = msg->sg.size; 416 if (psock->apply_bytes && psock->apply_bytes < tosend) 417 tosend = psock->apply_bytes; [...] 443 sk_msg_return(sk, msg, tosend); 444 release_sock(sk); 446 origsize = msg->sg.size; 447 ret = tcp_bpf_sendmsg_redir(sk_redir, redir_ingress, 448 msg, tosend, flags); 449 sent = origsize - msg->sg.size; [...] 454 lock_sock(sk); 455 if (unlikely(ret < 0)) { 456 int free = sk_msg_free_nocharge(sk, msg); 458 if (!cork) 459 *copied -= free; 460 } [...] 487 if (eval == __SK_REDIRECT) 488 sk_mem_charge(sk, tosend - sent); [...]
When running the selftest test_txmsg_redir_wait_sndmem with txmsg_apply, the following warning will be reported:
------------[ cut here ]------------ WARNING: CPU: 6 PID: 57 at net/ipv4/af_inet.c:156 inet_sock_destruct+0x190/0x1a0 Modules linked in: CPU: 6 UID: 0 PID: 57 Comm: kworker/6:0 Not tainted 6.12.0-rc1.bm.1-amd64+ #43 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 Workqueue: events sk_psock_destroy RIP: 0010:inet_sock_destruct+0x190/0x1a0 RSP: 0018:ffffad0a8021fe08 EFLAGS: 00010206 RAX: 0000000000000011 RBX: ffff9aab4475b900 RCX: ffff9aab481a0800 RDX: 0000000000000303 RSI: 0000000000000011 RDI: ffff9aab4475b900 RBP: ffff9aab4475b990 R08: 0000000000000000 R09: ffff9aab40050ec0 R10: 0000000000000000 R11: ffff9aae6fdb1d01 R12: ffff9aab49c60400 R13: ffff9aab49c60598 R14: ffff9aab49c60598 R15: dead000000000100 FS: 0000000000000000(0000) GS:ffff9aae6fd80000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007ffec7e47bd8 CR3: 00000001a1a1c004 CR4: 0000000000770ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: <TASK> ? __warn+0x89/0x130 ? inet_sock_destruct+0x190/0x1a0 ? report_bug+0xfc/0x1e0 ? handle_bug+0x5c/0xa0 ? exc_invalid_op+0x17/0x70 ? asm_exc_invalid_op+0x1a/0x20 ? inet_sock_destruct+0x190/0x1a0 __sk_destruct+0x25/0x220 sk_psock_destroy+0x2b2/0x310 process_scheduled_works+0xa3/0x3e0 worker_thread+0x117/0x240 ? __pfx_worker_thread+0x10/0x10 kthread+0xcf/0x100 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x31/0x40 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 </TASK> ---[ end trace 0000000000000000 ]---
In __SK_REDIRECT, a more concise way is delaying the uncharging after sent bytes are finalized, and uncharge this value. When (ret < 0), we shall invoke sk_msg_free.
Same thing happens in case __SK_DROP, when tosend is set to apply_bytes, we may miss uncharging (msg->sg.size - apply_bytes) bytes. The same warning will be reported in selftest.
[...] 468 case __SK_DROP: 469 default: 470 sk_msg_free_partial(sk, msg, tosend); 471 sk_msg_apply_bytes(psock, tosend); 472 *copied -= (tosend + delta); 473 return -EACCES; [...]
So instead of sk_msg_free_partial we can do sk_msg_free here.
Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface") Fixes: 8ec95b94716a ("bpf, sockmap: Fix the sk->sk_forward_alloc warning of sk_stream_kill_queues") Signed-off-by: Zijian Zhang zijianzhang@bytedance.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: John Fastabend john.fastabend@gmail.com Link: https://lore.kernel.org/bpf/20241016234838.3167769-3-zijianzhang@bytedance.c... Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv4/tcp_bpf.c | 11 ++++------- 1 file changed, 4 insertions(+), 7 deletions(-)
diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c index 915286c3615a2..0a42d73c0850e 100644 --- a/net/ipv4/tcp_bpf.c +++ b/net/ipv4/tcp_bpf.c @@ -441,7 +441,6 @@ static int tcp_bpf_send_verdict(struct sock *sk, struct sk_psock *psock, cork = true; psock->cork = NULL; } - sk_msg_return(sk, msg, tosend); release_sock(sk);
origsize = msg->sg.size; @@ -453,8 +452,9 @@ static int tcp_bpf_send_verdict(struct sock *sk, struct sk_psock *psock, sock_put(sk_redir);
lock_sock(sk); + sk_mem_uncharge(sk, sent); if (unlikely(ret < 0)) { - int free = sk_msg_free_nocharge(sk, msg); + int free = sk_msg_free(sk, msg);
if (!cork) *copied -= free; @@ -468,7 +468,7 @@ static int tcp_bpf_send_verdict(struct sock *sk, struct sk_psock *psock, break; case __SK_DROP: default: - sk_msg_free_partial(sk, msg, tosend); + sk_msg_free(sk, msg); sk_msg_apply_bytes(psock, tosend); *copied -= (tosend + delta); return -EACCES; @@ -484,11 +484,8 @@ static int tcp_bpf_send_verdict(struct sock *sk, struct sk_psock *psock, } if (msg && msg->sg.data[msg->sg.start].page_link && - msg->sg.data[msg->sg.start].length) { - if (eval == __SK_REDIRECT) - sk_mem_charge(sk, tosend - sent); + msg->sg.data[msg->sg.start].length) goto more_data; - } } return ret; }