[PATCH v2 net] mptcp: fix data stream corruption

[PATCH v2 net] mptcp: fix data stream corruption

[Paolo Abeni]

Maxim reported several issues when forcing a TCP transparent proxy
to use the MPTCP protocol for the inbound connections. He also
provided a clean reproducer.

The problem boils down to 'mptcp_frag_can_collapse_to()' assuming
that only MPTCP will use the given page_frag.

If others - e.g. the plain TCP protocol - allocate page fragments,
we can end-up re-using already allocated memory for mptcp_data_frag.

Fix the issue ensuring that the to-be-expanded data fragment is
located at the current page frag end.

v1 -> v2:
 - added missing fixes tag (Mat)

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/178
Reported-and-tested-by: Maxim Galaganov <max@internet.ru>
Fixes: 18b683bff89d ("mptcp: queue data for mptcp level retransmission")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
 net/mptcp/protocol.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 29a2d690d8d5..2d21a4793d9d 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -879,12 +879,18 @@ static bool mptcp_skb_can_collapse_to(u64 write_seq,
 	       !mpext->frozen;
 }
 
+/* we can append data to the given data frag if:
+ * - there is space available in the backing page_frag
+ * - the data frag tail matches the current page_frag free offset
+ * - the data frag end sequence number matches the current write seq
+ */
 static bool mptcp_frag_can_collapse_to(const struct mptcp_sock *msk,
 				       const struct page_frag *pfrag,
 				       const struct mptcp_data_frag *df)
 {
 	return df && pfrag->page == df->page &&
 		pfrag->size - pfrag->offset > 0 &&
+		pfrag->offset == (df->offset + df->data_len) &&
 		df->data_seq + df->data_len == msk->write_seq;
 }
 
-- 
2.26.2

Re: [PATCH v2 net] mptcp: fix data stream corruption

[Mat Martineau]

On Tue, 11 May 2021, Paolo Abeni wrote:

> Maxim reported several issues when forcing a TCP transparent proxy
> to use the MPTCP protocol for the inbound connections. He also
> provided a clean reproducer.
>
> The problem boils down to 'mptcp_frag_can_collapse_to()' assuming
> that only MPTCP will use the given page_frag.
>
> If others - e.g. the plain TCP protocol - allocate page fragments,
> we can end-up re-using already allocated memory for mptcp_data_frag.
>
> Fix the issue ensuring that the to-be-expanded data fragment is
> located at the current page frag end.
>
> v1 -> v2:
> - added missing fixes tag (Mat)
>
> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/178
> Reported-and-tested-by: Maxim Galaganov <max@internet.ru>
> Fixes: 18b683bff89d ("mptcp: queue data for mptcp level retransmission")
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> ---
> net/mptcp/protocol.c | 6 ++++++
> 1 file changed, 6 insertions(+)

Paolo -

Thanks for the tag fix. Patch looks good to me:

Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>


--
Mat Martineau
Intel

Re: [PATCH v2 net] mptcp: fix data stream corruption

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf.git (refs/heads/master):

On Tue, 11 May 2021 19:13:51 +0200 you wrote:
> Maxim reported several issues when forcing a TCP transparent proxy
> to use the MPTCP protocol for the inbound connections. He also
> provided a clean reproducer.
> 
> The problem boils down to 'mptcp_frag_can_collapse_to()' assuming
> that only MPTCP will use the given page_frag.
> 
> [...]

Here is the summary with links:
  - [v2,net] mptcp: fix data stream corruption
    https://git.kernel.org/bpf/bpf/c/29249eac5225

You are awesome, thank you!
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