On Tue, Aug 06, 2019 at 05:25:35PM +0200, Eric Dumazet wrote:
On Tue, Aug 6, 2019 at 5:09 PM Matthieu Baerts matthieu.baerts@tessares.net wrote:
From: Eric Dumazet edumazet@google.com
commit b617158dc096709d8600c53b6052144d12b89fab upstream.
Some applications set tiny SO_SNDBUF values and expect TCP to just work. Recent patches to address CVE-2019-11478 broke them in case of losses, since retransmits might be prevented.
We should allow these flows to make progress.
This patch allows the first and last skb in retransmit queue to be split even if memory limits are hit.
It also adds the some room due to the fact that tcp_sendmsg() and tcp_sendpage() might overshoot sk_wmem_queued by about one full TSO skb (64KB size). Note this allowance was already present in stable backports for kernels < 4.15
Note for < 4.15 backports : tcp_rtx_queue_tail() will probably look like :
static inline struct sk_buff *tcp_rtx_queue_tail(const struct sock *sk) { struct sk_buff *skb = tcp_send_head(sk);
return skb ? tcp_write_queue_prev(sk, skb) : tcp_write_queue_tail(sk);}
Fixes: f070ef2ac667 ("tcp: tcp_fragment() should apply sane memory limits") Signed-off-by: Eric Dumazet edumazet@google.com Reported-by: Andrew Prout aprout@ll.mit.edu Tested-by: Andrew Prout aprout@ll.mit.edu Tested-by: Jonathan Lemon jonathan.lemon@gmail.com Tested-by: Michal Kubecek mkubecek@suse.cz Acked-by: Neal Cardwell ncardwell@google.com Acked-by: Yuchung Cheng ycheng@google.com Acked-by: Christoph Paasch cpaasch@apple.com Cc: Jonathan Looney jtl@netflix.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Matthieu Baerts matthieu.baerts@tessares.net
Notes: Hello,
Here is the backport for linux-4.14.y branch simply by implementing functions written by Eric here in the commit message and in this email thread. It might be valid for older versions, I didn't check. In my setup with MPTCP, I had the same bug other had where TCP flows were stalled. The initial fix b6653b3629e5 (tcp: refine memory limit test in tcp_fragment()) from Eric was helping but the backport in < 4.15 was not looking safe: 1bc13903773b (tcp: refine memory limit test in tcp_fragment()). I then decided to test the new fix and it is working fine in my test environment, no stalled TCP flows in a few hours. In this email thread I see that Eric will push a patch for v4.14. I absolutely do not want to add pressure or steal his work but because I have the patch here and it is tested, I was thinking it could be a good idea to share it with others. Feel free to ignore this patch if needed. But if this patch can reduce a tiny bit Eric's workload, I would be very glad if it helps :) Because at the end, it is Eric's work, feel free to change my "Signed-off-by" by "Tested-By" if it is how it work or nothing if you prefer to wait for Eric's patch.This patch is fine, I was simply on vacation last week, and wanted to truly take full advantage of them ;)
Queued for 4.14, 4.9, and 4.4. Thanks all!
-- Thanks, Sasha