lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:   Mon, 14 Dec 2020 18:08:40 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Cambda Zhu <cambda@...ux.alibaba.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        netdev <netdev@...r.kernel.org>,
        Dust Li <dust.li@...ux.alibaba.com>,
        Tony Lu <tonylu@...ux.alibaba.com>
Subject: Re: [PATCH net-next] net: Limit logical shift left of TCP probe0
 timeout

On Sun, 13 Dec 2020 21:59:45 +0800 Cambda Zhu wrote:
> > On Dec 13, 2020, at 06:32, Jakub Kicinski <kuba@...nel.org> wrote:
> > On Tue,  8 Dec 2020 17:19:10 +0800 Cambda Zhu wrote:  
> >> For each TCP zero window probe, the icsk_backoff is increased by one and
> >> its max value is tcp_retries2. If tcp_retries2 is greater than 63, the
> >> probe0 timeout shift may exceed its max bits. On x86_64/ARMv8/MIPS, the
> >> shift count would be masked to range 0 to 63. And on ARMv7 the result is
> >> zero. If the shift count is masked, only several probes will be sent
> >> with timeout shorter than TCP_RTO_MAX. But if the timeout is zero, it
> >> needs tcp_retries2 times probes to end this false timeout. Besides,
> >> bitwise shift greater than or equal to the width is an undefined
> >> behavior.  
> > 
> > If icsk_backoff can reach 64, can it not also reach 256 and wrap?  
> 
> If tcp_retries2 is set greater than 255, it can be wrapped. But for TCP probe0,
> it seems to be not a serious problem. The timeout will be icsk_rto and backoff
> again. And considering icsk_backoff is 8 bits, not only it may always be lesser
> than tcp_retries2, but also may always be lesser than tcp_orphan_retries. And
> the icsk_probes_out is 8 bits too. So if the max_probes is greater than 255,
> the connection won’t abort even if it’s an orphan sock in some cases.
> 
> We can change the type of icsk_backoff/icsk_probes_out to fix these problems.
> But I think maybe the retries greater than 255 have no sense indeed and the RFC
> only requires the timeout(R2) greater than 100s at least. Could it be better to
> limit the min/max ranges of their sysctls?

All right, I think the patch is good as is, applied for 5.11, thank you!

Powered by blists - more mailing lists