[tor-bugs] #33346 [Core Tor/Tor]: Seccomp soft fail (no write) in 0.4.2.6

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#33346: Seccomp soft fail (no write) in 0.4.2.6
-------------------------------------------------+-------------------------
 Reporter:  subjectfrosting                      |          Owner:  nickm
     Type:  defect                               |         Status:
                                                 |  needs_revision
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  0.4.4.x-final
Component:  Core Tor/Tor                         |        Version:  0.4.2.6
 Severity:  Normal                               |     Resolution:
 Keywords:  easy? 035-backport 041-backport      |  Actual Points:  .1
  042-backport 043-backport                      |
Parent ID:                                       |         Points:  .1
 Reviewer:                                       |        Sponsor:
-------------------------------------------------+-------------------------

Comment (by subjectfrosting):

 Nick and I discussed this on IRC earlier. I did try tampering with the
 flags that we give openat() but no luck. I was able to reproduce the bug
 on my amd64 machine too, so it is not ARM related.

 Let me know if there's anything further I can try out. Nick suggested it
 was likely to be one of two things:
 * seccomp2 is not adding the rule that we think
 * using wrong pointer for the file (must match handle, not just same
 string)

 I added my own logging on nick's request to see if the right path was
 being detected, but this seemed normal:
 {{{
 write(1, "seccomp: allow_file_open called "..., 51seccomp: allow_file_open
 called with use_openat:1
 ) = 51
 write(1, "seccomp: allow_file_open called "..., 75seccomp: allow_file_open
 called with file:/home/user/.tor/cached-consensus
 openat(AT_FDCWD, "/home/user/.tor/cached-consensus", O_RDONLY|O_CLOEXEC) =
 -1 EPERM (Operation not permitted)
 write(1, "Mar 09 16:30:06.000 [warn] Could"..., 112Mar 09 16:30:06.000
 [warn] Could not open "/home/user/.tor/cached-consensus" for mmap():
 Operation not permitted
 }}}


 An except of my strace:
 {{{
 ...
 getpid()                                = 22986
 sendto(7, "<29>Mar  9 14:26:07 Tor[22986]: "..., 69, MSG_NOSIGNAL, NULL,
 0) = 69
 unlinkat(AT_FDCWD, "/var/lib/tor/data/key-pinning-entries", 0) = -1 ENOENT
 (No such file or directory)
 openat(AT_FDCWD, "/var/lib/tor/data/cached-certs", O_RDONLY|O_CLOEXEC) =
 -1 EPERM (Operation not permitted)
 getpid()                                = 22986
 sendto(7, "<28>Mar  9 14:26:07 Tor[22986]: "..., 105, MSG_NOSIGNAL, NULL,
 0) = 105
 openat(AT_FDCWD, "/var/lib/tor/data/cached-consensus", O_RDONLY|O_CLOEXEC)
 = -1 EPERM (Operation not permitted)
 getpid()                                = 22986
 sendto(7, "<28>Mar  9 14:26:07 Tor[22986]: "..., 120, MSG_NOSIGNAL, NULL,
 0) = 120
 openat(AT_FDCWD, "/var/lib/tor/data/unverified-consensus",
 O_RDONLY|O_CLOEXEC) = -1 EPERM (Operation not permitted)
 getpid()                                = 22986
 sendto(7, "<28>Mar  9 14:26:07 Tor[22986]: "..., 124, MSG_NOSIGNAL, NULL,
 0) = 124
 openat(AT_FDCWD, "/var/lib/tor/data/cached-microdesc-consensus",
 O_RDONLY|O_CLOEXEC) = -1 EPERM (Operation not permitted)
 getpid()                                = 22986
 sendto(7, "<28>Mar  9 14:26:07 Tor[22986]: "..., 130, MSG_NOSIGNAL, NULL,
 0) = 130
 openat(AT_FDCWD, "/var/lib/tor/data/unverified-microdesc-consensus",
 O_RDONLY|O_CLOEXEC) = -1 EPERM (Operation not permitted)
 getpid()                                = 22986
 sendto(7, "<28>Mar  9 14:26:07 Tor[22986]: "..., 134, MSG_NOSIGNAL, NULL,
 0) = 134
 openat(AT_FDCWD, "/var/lib/tor/data/cached-microdescs",
 O_RDONLY|O_CLOEXEC) = -1 EPERM (Operation not permitted)
 getpid()                                = 22986
 sendto(7, "<28>Mar  9 14:26:07 Tor[22986]: "..., 121, MSG_NOSIGNAL, NULL,
 0) = 121
 openat(AT_FDCWD, "/var/lib/tor/data/cached-microdescs.new",
 O_RDONLY|O_CLOEXEC) = -1 EPERM (Operation not permitted)
 getpid()                                = 22986
 sendto(7, "<28>Mar  9 14:26:07 Tor[22986]: "..., 114, MSG_NOSIGNAL, NULL,
 0) = 114
 openat(AT_FDCWD, "/var/lib/tor/data/cached-descriptors",
 O_RDONLY|O_CLOEXEC) = -1 EPERM (Operation not permitted)
 getpid()                                = 22986
 sendto(7, "<28>Mar  9 14:26:07 Tor[22986]: "..., 122, MSG_NOSIGNAL, NULL,
 0) = 122
 newfstatat(AT_FDCWD, "/var/lib/tor/data/cached-descriptors.new",
 0x7fefcc0258, 0) = -1 EPERM (Operation not permitted)
 openat(AT_FDCWD, "/var/lib/tor/data/cached-extrainfo", O_RDONLY|O_CLOEXEC)
 = -1 EPERM (Operation not permitted)
 getpid()                                = 22986
 sendto(7, "<28>Mar  9 14:26:07 Tor[22986]: "..., 120, MSG_NOSIGNAL, NULL,
 0) = 120
 newfstatat(AT_FDCWD, "/var/lib/tor/data/cached-extrainfo.new",
 0x7fefcc0258, 0) = -1 EPERM (Operation not permitted)
 getpid()                                = 22986
 sendto(7, "<29>Mar  9 14:26:07 Tor[22986]: "..., 70, MSG_NOSIGNAL, NULL,
 0) = 70
 epoll_ctl(3, EPOLL_CTL_ADD, 6, {EPOLLIN, {u32=6, u64=6}}) = 0
 epoll_ctl(3, EPOLL_CTL_ADD, 4, {EPOLLIN, {u32=4, u64=4}}) = 0
 epoll_pwait(3, ^C0x558e1975d0, 32, 1000, NULL, 8) = -1 EINTR (Interrupted
 system call)
 strace: Process 22986 detached
 }}}

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/33346#comment:7>
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