[Bug libc/12539] New: need a way to atomically set FD_CLOEXEC on fds transferred via SCM_RIGHTS

[Bug libc/12539] New: need a way to atomically set FD_CLOEXEC on fds transferred via SCM_RIGHTS

[eblake at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12539

           Summary: need a way to atomically set FD_CLOEXEC on fds
                    transferred via SCM_RIGHTS
           Product: glibc
           Version: 2.13
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: drepper.fsp@gmail.com
        ReportedBy: eblake@redhat.com


It seems a shame that after all the effort that went into allowing atomic
creation of fds with FD_CLOEXEC set (accept4, pipe2, epoll_create1, ...) that
there's still no way to transfer fds using recvmsg while having the resulting
fd start life as cloexec.  This is a two-part bug report - the kernel would
need to learn SCM_RIGHTS_CLOEXEC (identical behavior to SCM_RIGHTS on sendmsg,
and atomically sets FD_CLOEXEC on recvmsg), and glibc needs to learn to use it.

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[Bug libc/12539] need a way to atomically set FD_CLOEXEC on fds transferred via SCM_RIGHTS

[bonzini at gnu dot org]

http://sourceware.org/bugzilla/show_bug.cgi?id=12539

Paolo Bonzini <bonzini at gnu dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bonzini at gnu dot org
         Resolution|                            |INVALID

--- Comment #1 from Paolo Bonzini <bonzini at gnu dot org> 2011-03-04 16:16:43 UTC ---
This is already present, but the choice of whether to close-on-exec is done by
the receiver, not the sender:

   MSG_CMSG_CLOEXEC (recvmsg() only; since Linux 2.6.23)
          Set  the close-on-exec flag for the file descriptor received via a
Unix 
          domain file descriptor using the SCM_RIGHTS operation (described in 
          unix(7)).  This flag is useful for the same reasons as the O_CLOEXEC
          flag of open(2).

/* Bits in the FLAGS argument to `send', `recv', et al.  */
enum
  {
    MSG_CMSG_CLOEXEC    = 0x40000000    /* Set close_on_exit for file
                                           descriptor received through
                                           SCM_RIGHTS.  */
#define MSG_CMSG_CLOEXEC MSG_CMSG_CLOEXEC
  };

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[Bug libc/12539] need a way to atomically set FD_CLOEXEC on fds transferred via SCM_RIGHTS

[eblake at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12539

--- Comment #2 from Eric Blake <eblake at redhat dot com> 2011-03-04 17:09:16 UTC ---
Since 'man recvmsg' doesn't describe SCM_RIGHTS (other than the one mention of
the term in MSG_CMSG_CLOEXEC), and 'man csmg' didn't discuss MSG_CMSG_CLOEXEC,
I hadn't put two and two together.  Thanks for correcting me, and glad to know
it already exists.

Hmm, that means I should open a bug against the man-pages project.  'man cmsg'
only talks about SCM_RIGHTS creating descriptors as if by dup(2), but it should
also discuss that the addition of the MSG_CMSG_CLOEXEC flags can create
descriptors as if by fcntl(,F_DUPFD_CLOEXEC,0) instead.

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[Bug libc/12539] need a way to atomically set FD_CLOEXEC on fds transferred via SCM_RIGHTS

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=12539

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-

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