[tor-bugs] #21312 [Obfuscation/Snowflake]: snowflake-client is pegged at 100% cpu

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#21312: snowflake-client is pegged at 100% cpu
-----------------------------------+--------------------------------
 Reporter:  arlolra                |          Owner:  arlolra
     Type:  defect                 |         Status:  needs_revision
 Priority:  High                   |      Milestone:
Component:  Obfuscation/Snowflake  |        Version:
 Severity:  Major                  |     Resolution:
 Keywords:                         |  Actual Points:
Parent ID:                         |         Points:
 Reviewer:                         |        Sponsor:
-----------------------------------+--------------------------------

Comment (by dcf):

 Replying to [comment:29 dcf]:
 > Stand by. The server-webrtc process stopped running for some reason. I'm
 not sure if it's related to the patch or not. I'll try running it again
 with a debugger attached.

 Here's a server-webrtc segfault from gdb.

 {{{
 Thread 6 "server-webrtc" received signal SIGSEGV, Segmentation fault.
 [Switching to Thread 0x7f3d20f11700 (LWP 14901)]
 0x0000000000000000 in ?? ()
 (gdb) bt
 #0  0x0000000000000000 in ?? ()
 #1  0x000055cc34c659c8 in CGO_Channel_Send (channel=0x7f3cf401b2c0,
 data=0xc42019a000, size=<optimized out>,
     binary=<optimized out>) at /home/david/go/src/github.com/keroserene
 /go-webrtc/datachannel.cc:19
 #2  0x000055cc34aa7570 in runtime.asmcgocall () at
 /usr/lib/go-1.7/src/runtime/asm_amd64.s:590
 #3  0x000000c420022cd0 in ?? ()
 #4  0x000055cc34a5114d in runtime.cgocall (fn=0x0, arg=0xc4200c81a0,
 ~r2=552668856)
     at /usr/lib/go-1.7/src/runtime/cgocall.go:115
 #5  0x000000c42001b500 in ?? ()
 #6  0x0000000000000000 in ?? ()
 }}}
 It's happening in the call to `c.dc.Send(b)` inside `webRTCConn.Write`. (I
 added a logging statement right after the `Send` that didn't get called.)

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/21312#comment:31>
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