Re: [tor-bugs] #20283 [Applications/Tor Browser]: Tor Browser should run without a `/proc` filesystem.

["Tor Bug Tracker & Wiki" <blackhole@xxxxxxxxxxxxxx>]

#20283: Tor Browser should run without a `/proc` filesystem.
-------------------------------------------------+-------------------------
 Reporter:  yawning                              |          Owner:
                                                 |  pospeselr
     Type:  defect                               |         Status:
                                                 |  needs_review
 Priority:  Very High                            |      Milestone:
Component:  Applications/Tor Browser             |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  tbb-sandboxing,                      |  Actual Points:
  TorBrowserTeam201804R                          |
Parent ID:  #20773                               |         Points:
 Reviewer:                                       |        Sponsor:
-------------------------------------------------+-------------------------

Comment (by pospeselr):

 Audited all the remaining syscalls (was only catch'ing open and openat
 before) and discovered three more things which don't seem to be an issue
 for us.  Here's the full list of what we're working with (on x64 Linux)
 roughly in order of invocation for future reference (open here covers both
 open and openat, didn't save that data unfortunately):

 ||= Caller =||= syscall =||= Requested Path =||= Relevant Source ||
 || mozilla::HasUserNamespaceSupport() || access || "/proc/self/ns/user" ||
 /security/sandbox/linux/SandboxInfo.cpp ||
 |||||||| Failure here 'just' disables 'User Namespaces' (as shown under
 the Sandbox section of about:support), not sure what the security
 consequences of this is but tor browser boots and runs fine ||
 || selinuxfs_exists() || open ||"/proc/filessytems" ||  ||
 |||||||| This call happens down in dlopen when opening libxul.so. Failure
 to open this file will result in selinxufs_exists() always reporting
 selinuxfs exists ( see
 [https://github.com/SELinuxProject/selinux/blob/64afa1aff1cd610d2493f780e2a44b551f668b84/libselinux/src/init.c#L56
 selinuxfs_exists(void)] but everything seems to go along even if it is a
 false positive) ||
 || mozilla::(anonymous namespace)::IsSingleThreaded () || xstat ||
 "/proc/self/task" || /security/sandbox/linux/SandboxInfo.cpp ||
 |||||||| Failure to read and count number of files under this directory
 causes tor browser to guess and indicate that it is not single threaded ||
 || mozilla::ComputeProcessUptimeThread(void*) || open ||
 "/proc/self/task/$tid/stat", "/proc/self/stat" ||
 /mozglue/misc/TimeStamp_posix.cpp ||
 |||||||| This code fails gracefully and sets uptime to 0 ||
 || nsNotifyAddrListener::calculateNetworkId() || open ||
 "/proc/net/route", "/proc/net/arp" ||
 /netwerk/system/linux/nsNotifyAddrListener_Linux.cpp ||
 |||||||| This code fails gracefully, network id is only used once for
 telemetry, otherwise this is dead code ||
 || js::GetNativeStackBaseImpl() || open || "/proc/self/maps" ||
 /js/src/jsnativestack.cpp ||
 |||||||| This code gets an address at the top of the usable stack,
 required for internal JS stuff or else bad things happen. Attached patch
 fixes this issue using !__libc_stack_end ||
 || mozilla::ThreadStackHelper::GetThreadStackBase() || open ||
 "/proc/self/maps" || /xpcom/threads/ThreadStackHelper.cpp ||
 |||||||| Similar to js::GetNativeStackBaseImpl() except the implementation
 isn't there for all platforms and the saved value isn't used for anything,
 fails gracefully ||
 || nsSystemInfo::Init() || open || "/proc/cpuino" ||
 /xpcom/base/nsSystemInfo.cpp ||
 |||||||| Fails gracefully, otherwise scrapes all your CPU info and stores
 it in the nsISystemInfo property bag for god knows what reasons ||
 || gfxFcPlatformFontList::FindGenericFamilies() || readlink ||
 "/proc/self/exe" || /gfx/thebes/gfxFcPlatformFontList.cpp ||
 |||||||| Fails gracefully when intercepting this syscall and returning
 error (-1) ||
 || nsLocalFile::GetDiskSpaceAvailable() || open || "/proc/self/mountinfo"
 || /xpcom/io/nsLocalFileUnix.cpp ||
 |||||||| Fails gracefully when given file isn't found and a simpler
 estimate is used instead ||

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/20283#comment:22>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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