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Fix atomicity violation in network-devp2p #11277
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dvdplm
approved these changes
Nov 21, 2019
| @@ -220,14 +220,13 @@ impl Connection { | |||
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| /// Register this connection with the IO event loop. | |||
| pub fn register_socket<Host: Handler>(&self, reg: Token, event_loop: &mut EventLoop<Host>) -> io::Result<()> { | |||
| if self.registered.load(AtomicOrdering::SeqCst) { | |||
| if self.registered.compare_and_swap(false, true, AtomicOrdering::SeqCst) { | |||
| return Ok(()); | |||
| } | |||
| trace!(target: "network", "connection register; token={:?}", reg); | |||
| if let Err(e) = event_loop.register(&self.socket, reg, self.interest, PollOpt::edge() /* | PollOpt::oneshot() */) { // TODO: oneshot is broken on windows | |||
| trace!(target: "network", "Failed to register {:?}, {:?}", reg, e); | |||
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I wonder why we don't return here (and set self.registered back to false).
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I wonder the same, @arkpar cfb8671#diff-c378e114f762560f980403b3e66392dcL140-L142?
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@arkpar I'll go ahead and merge this now, but I'm still curious. :)
ordian
approved these changes
Dec 5, 2019
dvdplm
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Dec 15, 2019
…ate their data instead Merge branch 'master' into dp/chore/kvdb-no-default-column * master: tx-q: enable basic verification of local transactions (#11332) remove null signatures (#11335) ethcore/res: activate agharta on classic 9573000 (#11331) [secretstore] migrate to version 4 (#11322) Enable EIP-2384 for ice age hard fork (#11281) Fix atomicity violation in network-devp2p (#11277)
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It is to fix an atomicity violation in network-devp2p.
https://github.com/paritytech/parity-ethereum/blob/ee016127686f6cc63815b15d7df5aa22f4edc22c/util/network-devp2p/src/connection.rs#L222-L232
Following the same bug pattern of #5910
In function register_socket:
It seems that the atomic variable is used to guarantee that the inner code will only be executed once in multiple calls.
The function takes &self (instead of &mut self) and I think it may be called in different threads simultaneously.
If that is the case, the following execution path may happen:
The atomicity violation happens because the read and write of one atomic variable are interleaved by another write.
The fix is to use one compare_and_swap to replace the separate load and store, as shown in the fix.
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