[tor-bugs] #20775 [Applications/Tor Browser Sandbox]: Use Tor Browser's integrated `AF_LOCAL` support on alpha.

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#20775: Use Tor Browser's integrated `AF_LOCAL` support on alpha.
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 Reporter:  yawning                           |          Owner:  yawning
     Type:  enhancement                       |         Status:  assigned
 Priority:  Medium                            |      Milestone:
Component:  Applications/Tor Browser Sandbox  |        Version:
 Severity:  Normal                            |     Resolution:
 Keywords:                                    |  Actual Points:
Parent ID:                                    |         Points:
 Reviewer:                                    |        Sponsor:
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Comment (by yawning):

 Unsandboxed Tor Browser 7.0.1:
 {{{
 socket(AF_INET, SOCK_STREAM, IPPROTO_IP) = 67
 fcntl(67, F_GETFL)                      = 0x2 (flags O_RDWR)
 fcntl(67, F_SETFL, O_RDWR|O_NONBLOCK)   = 0
 socket(AF_INET6, SOCK_STREAM, IPPROTO_IP) = 68
 close(68)                               = 0
 socket(AF_INET6, SOCK_STREAM, IPPROTO_IP) = 68
 fcntl(68, F_GETFL)                      = 0x2 (flags O_RDWR)
 fcntl(68, F_SETFL, O_RDWR|O_NONBLOCK)   = 0
 close(68)                               = 0
 setsockopt(67, SOL_TCP, TCP_NODELAY, [1], 4) = 0

 socket(AF_UNIX, SOCK_STREAM, 0)         = 68
 fcntl(68, F_GETFL)                      = 0x2 (flags O_RDWR)
 fcntl(68, F_SETFL, O_RDWR|O_NONBLOCK)   = 0
 close(67)                               = 0
 connect(68, {sa_family=AF_UNIX, sun_path="/var/run/tor/socks"}, 106) = 0
 }}}

 Without looking into the Firefox source, what I assume is happening in my
 branch is that the creation of the `AF_INET`/`AF_INET6` sockets fail (with
 `ENOSYS`) due to the seccomp-bpf rules, and Firefox decides not to
 actually open the connection that will work.

 When Tor Browser is configured to use `AF_LOCAL`, the two prior calls
 shouldn't happen to begin with.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/20775#comment:7>
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