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From: John Fastabend <john.fastabend@gmail.com>
To: jakub@cloudflare.com, daniel@iogearbox.net
Cc: netdev@vger.kernel.org, bpf@vger.kernel.org,
	john.fastabend@gmail.com, ast@kernel.org
Subject: [PATCH 2/2] bpf: sockmap, bpf_tcp_ingress needs to subtract bytes from sg.size
Date: Mon, 04 May 2020 10:21:44 -0700
Message-ID: <158861290407.14306.5327773422227552482.stgit@john-Precision-5820-Tower> (raw)
In-Reply-To: <158861271707.14306.15853815339036099229.stgit@john-Precision-5820-Tower>

In bpf_tcp_ingress we used apply_bytes to subtract bytes from sg.size
which is used to track total bytes in a message. But this is not
correct because apply_bytes is itself modified in the main loop doing
the mem_charge.

Then at the end of this we have sg.size incorrectly set and out of
sync with actual sk values. Then we can get a splat if we try to
cork the data later and again try to redirect the msg to ingress. To
fix instead of trying to track msg.size do the easy thing and include
it as part of the sk_msg_xfer logic so that when the msg is moved the
sg.size is always correct.

To reproduce the below users will need ingress + cork and hit an
error path that will then try to 'free' the skmsg.

[  173.699981] BUG: KASAN: null-ptr-deref in sk_msg_free_elem+0xdd/0x120
[  173.699987] Read of size 8 at addr 0000000000000008 by task test_sockmap/5317

[  173.700000] CPU: 2 PID: 5317 Comm: test_sockmap Tainted: G          I       5.7.0-rc1+ #43
[  173.700005] Hardware name: Dell Inc. Precision 5820 Tower/002KVM, BIOS 1.9.2 01/24/2019
[  173.700009] Call Trace:
[  173.700021]  dump_stack+0x8e/0xcb
[  173.700029]  ? sk_msg_free_elem+0xdd/0x120
[  173.700034]  ? sk_msg_free_elem+0xdd/0x120
[  173.700042]  __kasan_report+0x102/0x15f
[  173.700052]  ? sk_msg_free_elem+0xdd/0x120
[  173.700060]  kasan_report+0x32/0x50
[  173.700070]  sk_msg_free_elem+0xdd/0x120
[  173.700080]  __sk_msg_free+0x87/0x150
[  173.700094]  tcp_bpf_send_verdict+0x179/0x4f0
[  173.700109]  tcp_bpf_sendpage+0x3ce/0x5d0

Fixes: 604326b41a6fb ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
---
 include/linux/skmsg.h |    1 +
 net/ipv4/tcp_bpf.c    |    1 -
 2 files changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
index 8a709f6..ad31c9f 100644
--- a/include/linux/skmsg.h
+++ b/include/linux/skmsg.h
@@ -187,6 +187,7 @@ static inline void sk_msg_xfer(struct sk_msg *dst, struct sk_msg *src,
 	dst->sg.data[which] = src->sg.data[which];
 	dst->sg.data[which].length  = size;
 	dst->sg.size		   += size;
+	src->sg.size		   -= size;
 	src->sg.data[which].length -= size;
 	src->sg.data[which].offset += size;
 }
diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
index ff96466..629aaa9a 100644
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -125,7 +125,6 @@ static int bpf_tcp_ingress(struct sock *sk, struct sk_psock *psock,
 
 	if (!ret) {
 		msg->sg.start = i;
-		msg->sg.size -= apply_bytes;
 		sk_psock_queue_msg(psock, tmp);
 		sk_psock_data_ready(sk, psock);
 	} else {


  parent reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-04 17:21 [PATCH 0/2] sockmap, fix for some error paths with helpers John Fastabend
2020-05-04 17:21 ` [PATCH 1/2] bpf: sockmap, msg_pop_data can incorrecty set an sge length John Fastabend
2020-05-05 18:59   ` Martin KaFai Lau
2020-05-04 17:21 ` John Fastabend [this message]
2020-05-05 19:05   ` [PATCH 2/2] bpf: sockmap, bpf_tcp_ingress needs to subtract bytes from sg.size Martin KaFai Lau
2020-05-05  9:30 ` [PATCH 0/2] sockmap, fix for some error paths with helpers Jakub Sitnicki
2020-05-05 22:28 ` Daniel Borkmann

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