Hi John,
On Wed, 2024-07-03 at 09:54 +0800, Geliang Tang wrote:
On Tue, 2024-07-02 at 18:03 -0700, John Fastabend wrote:
Geliang Tang wrote:
From: Geliang Tang tanggeliang@kylinos.cn
Run this BPF selftests (./test_progs -t sockmap_basic) on a Loongarch platform, a Kernel panic occurs:
''' Oops[#1]: CPU: 22 PID: 2824 Comm: test_progs Tainted: G OE 6.10.0- rc2+ #18 Hardware name: LOONGSON Dabieshan/Loongson-TC542F0, BIOS Loongson- UDK2018 ... ... ra: 90000000048bf6c0 sk_msg_recvmsg+0x120/0x560 ERA: 9000000004162774 copy_page_to_iter+0x74/0x1c0 CRMD: 000000b0 (PLV0 -IE -DA +PG DACF=CC DACM=CC -WE) PRMD: 0000000c (PPLV0 +PIE +PWE) EUEN: 00000007 (+FPE +SXE +ASXE -BTE) ECFG: 00071c1d (LIE=0,2-4,10-12 VS=7) ESTAT: 00010000 [PIL] (IS= ECode=1 EsubCode=0) BADV: 0000000000000040 PRID: 0014c011 (Loongson-64bit, Loongson-3C5000) Modules linked in: bpf_testmod(OE) xt_CHECKSUM xt_MASQUERADE xt_conntrack Process test_progs (pid: 2824, threadinfo=0000000000863a31, task=...) Stack : ... ... Call Trace: [<9000000004162774>] copy_page_to_iter+0x74/0x1c0 [<90000000048bf6c0>] sk_msg_recvmsg+0x120/0x560 [<90000000049f2b90>] tcp_bpf_recvmsg_parser+0x170/0x4e0 [<90000000049aae34>] inet_recvmsg+0x54/0x100 [<900000000481ad5c>] sock_recvmsg+0x7c/0xe0 [<900000000481e1a8>] __sys_recvfrom+0x108/0x1c0 [<900000000481e27c>] sys_recvfrom+0x1c/0x40 [<9000000004c076ec>] do_syscall+0x8c/0xc0 [<9000000003731da4>] handle_syscall+0xc4/0x160
Code: ...
---[ end trace 0000000000000000 ]--- Kernel panic - not syncing: Fatal exception Kernel relocated by 0x3510000 .text @ 0x9000000003710000 .data @ 0x9000000004d70000 .bss @ 0x9000000006469400 ---[ end Kernel panic - not syncing: Fatal exception ]--- '''
This crash happens every time when running sockmap_skb_verdict_shutdown subtest in sockmap_basic.
This crash is because a NULL pointer is passed to page_address() in sk_msg_recvmsg(). Due to the difference in architecture, page_address(0) will not trigger a panic on the X86 platform but will panic on the Loogarch platform. So this bug was hidden on the x86 platform, but now it is exposed on the Loogarch platform.
The root cause is an empty skb (skb->len == 0) is put on the queue.
In this case, in sk_psock_skb_ingress_enqueue(), num_sge is zero, and no page is put to this sge (see sg_set_page in sg_set_page), but this empty sge is queued into ingress_msg list.
And in sk_msg_recvmsg(), this empty sge is used, and a NULL page is got by sg_page(sge). Pass this NULL-page to copy_page_to_iter(), it passed to kmap_local_page() and page_address(), then kernel panics.
To solve this, we should prevent empty skb from putting on the queue. So in sk_psock_verdict_recv(), if the skb->len is zero, drop this skb.
Fixes: ef5659280eb1 ("bpf, sockmap: Allow skipping sk_skb parser program") Signed-off-by: Geliang Tang tanggeliang@kylinos.cn
net/core/skmsg.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/core/skmsg.c b/net/core/skmsg.c index fd20aae30be2..44952cdd1425 100644 --- a/net/core/skmsg.c +++ b/net/core/skmsg.c @@ -1184,7 +1184,7 @@ static int sk_psock_verdict_recv(struct sock *sk, struct sk_buff *skb) rcu_read_lock(); psock = sk_psock(sk);
- if (unlikely(!psock)) {
- if (unlikely(!psock || !len)) {
len = 0; tcp_eat_skb(sk, skb); sock_drop(sk, skb);
The skb->len == 0 here is the FIN pkt right? We are using the EFAULT return triggered by copy_page_to_iter to check for is_fin in tcp_bpf.c.
I added some logs for debugging and found that this FIN packet do hit is_fin check in tcp_bpf.c.
The concern I have here is if we don't have the skb fin pkt on the recv queue we might go into wait_data and block instead of return to user when rcvmsg() is called from user. I wonder if we can write a test for this if we don't already have one we probably should create one.
In test_sockmap_skb_verdict_shutdown(), the FIN packet is sent by
shutdown(p1, SHUT_WR);
and received by
n = recv(c1, &b, 1, SOCK_NONBLOCK); ASSERT_EQ(n, 0, "recv_timeout(fin)");
I think this test has covered the FIN packet scenario already. No need to add a new one. WDYT?
Maybe a better fix assuming my assumption about fin being skb-
len=0
is correct?
Thanks John. Your fix is much better than mine. I'll use this as v5 and update the commit log. I'll add your "Suggested-by" tag in it.
Anyway, this v5 (skmsg: skip zero length skb in sk_msg_recvmsg) seems ready to be merged.
Thanks, -Geliang
-Geliang
diff --git a/net/core/skmsg.c b/net/core/skmsg.c index fd20aae30be2..bbf40b999713 100644 --- a/net/core/skmsg.c +++ b/net/core/skmsg.c @@ -434,7 +434,8 @@ int sk_msg_recvmsg(struct sock *sk, struct sk_psock *psock, struct msghdr *msg, page = sg_page(sge); if (copied + copy > len) copy = len - copied; - copy = copy_page_to_iter(page, sge->offset, copy, iter); + if (copy) + copy = copy_page_to_iter(page, sge-
offset, copy, iter);
if (!copy) { copied = copied ? copied : -EFAULT; goto out;
Thanks, John