bpf, sockmap: bpf_tcp_ingress needs to subtract bytes from sg.size

[ Upstream commit 81aabbb9fb7b4b1efd073b62f0505d3adad442f3 ]

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>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/158861290407.14306.5327773422227552482.stgit@john-Precision-5820-Tower
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
index 14d61bba0b79bd0e8cc48c24fc84970546537a4f..71db17927a9da8ca52bad2851fc1384ca40cf3e0 100644 (file)
--- 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 8a01428f80c1c4b23e2ae0568efb2aa0e0f71ccb..19bd10e6ab830463f70387b8abbf40caf1e346ec 100644 (file)
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -200,7 +200,6 @@ 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 {