[MacPorts] #59497: openssh @8.1p1: sshd only works in debug mode

[MacPorts]

#59497: openssh @8.1p1: sshd only works in debug mode
-------------------------+--------------------------------------
  Reporter:  davidfavor  |      Owner:  Mihai Moldovan <ionic@…>
      Type:  defect      |     Status:  closed
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:  2.6.2
Resolution:  fixed       |   Keywords:
      Port:  openssh     |
-------------------------+--------------------------------------
Changes (by Mihai Moldovan <ionic@…>):

 * owner:  (none) => Mihai Moldovan <ionic@…>
 * status:  reopened => closed
 * resolution:   => fixed


Comment:

 In [changeset:"4adcdc8b8e606bb55f83b33a2c60362292a99066/macports-ports"
 4adcdc8b8e606bb55f83b33a2c60362292a99066/macports-ports] (master):
 {{{
 #!ConfigurableCommitTicketReference repository="macports-ports"
 revision="4adcdc8b8e606bb55f83b33a2c60362292a99066"
 net/openssh: fix sshd failure in non-debug mode. Revbump.

 This commit message is essentially just a copy of the source code comment.

 ssh_sandbox_child() has the side-effect of disabling opening new files.
 This is a security precaution to prevent the child process from leaking
 data or opening new sockets, but clashes with newer OpenSSL
 implementations.

 Generally, OpenSSL wants to read new entropy from the system for each
 reseeding operation (and, by extension, through any operation that might
 trigger an internal reseeding, like requesting random bytes).

 The current OpenSSL port only enables the default set of system entropy
 - which means reading in data from crypto devices like /dev/{,u,s}random
 and /dev/hwrng.

 To speed things up, OpenSSL tries to open file descriptors to the listed
 devices and caches the result, i.e., the open file descriptor. Those are
 normally kept open UNLESS a reading error occurred OR no random bytes
 were returned.

 In a quite scary move, OpenSSL versions prior to 1.1.1 didn't fail when
 getting system entropy wasn't successful and also added some
 "pseudo-random" data like the PID, user id and current time to the
 entropy pool, which was often enough to seed the PRNG.

 More recent versions have a rewritten PRNG/DRBG core and, crucially,
 stricter rules when it comes to acquiring system entropy - this is now
 strictly required and no other data is mixed into the pool.

 OpenSSH generally tries (or intends) to leave crypto devices (which
 should one of the earliest open devices) alone and not close their FD on
 re-exec, but that doesn't seem to work. Although OpenSSL is initialized
 very early in the main() call chain, which SHOULD lead to open file
 descriptors to crypto devices, on a typical OS X/macOS system,
 /dev/urandom is opened as FD 6, which is above any FD that would be
 preserved after a re-exec operation.

 This leads to the child process having no open file descriptors to
 /dev/urandom, activating the sandbox, setting the number of open files
 to zero and subsequently effectively breaking OpenSSL 1.1.1+.

 We'll work around that by reseeding the PRNGs before enabling the
 sandbox, which has the side-effect of opening a file descriptor to
 /dev/urandom and keeping it open.

 There is a slight catch: errors in reading from the FD or a read count
 of zero (i.e., the device not returning any data) will lead to the FD
 being closed again without a way to be re-opened.

 We can take this risk, as this should realistically not happen. Even if
 it does, that only means that the child process will fail to read random
 data and hence terminate with an error - showing the same symptoms the
 workaround is intended to fix, but nothing worse.

 Fixes: https://trac.macports.org/ticket/59497
 }}}

-- 
Ticket URL: <https://trac.macports.org/ticket/59497#comment:17>
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