git: kernel - Fix long-standing bug in kqueue backend for *poll*()

[Matthew Dillon]

commit 0d47c594fde0de2008b2f26db9ab7a6a22eaf64f
Author: Matthew Dillon <dillon at apollo.backplane.com>
Date:   Tue Jan 23 13:00:54 2024 -0800

    kernel - Fix long-standing bug in kqueue backend for *poll*()
    
    * The poll() family of system calls passes an fds[] array with a
      series of descriptors and event requests.  Our kernel implementation
      uses kqueue but a long standing bug breaks situations where
      more than one fds[] entry for the poll corresponds to the same
      { ident, filter } for kqueue, causing only the last such entry
      to be registered with kqueue and breaking poll().
    
    * Added feature to kqueue to supply further distinctions between
      knotes beyond the nominal { kq, filter, ident } tuple, allowing
      us to fix poll().
    
    * Added a FreeBSD feature where poll() implements an implied POLLHUP
      when events = 0.  This is used by X11 and (perhaps mistakenly) also
      by sshd.  Our poll previous ignored fds[] entries with events = 0.
    
    * Note that sshd can generate poll fds[] arrays with both an events = 0
      and an events = POLLIN for the same descriptor, which broke sshd
      when I initially added the events = 0 support due to the first bug.
    
      Now with that fixed, sshd works properly.  However it is unclear whether
      the authors of sshd intended events = 0 to detect POLLHUP or not.
    
    Reported-by: servik (missing events = 0 poll feature)
    Testing: servik, dillon

Summary of changes:
 sys/kern/kern_event.c  | 36 +++++++++++++++++++++++++++------
 sys/kern/sys_generic.c | 54 +++++++++++++++++++++++++++++++++++++++++---------
 sys/sys/event.h        |  5 ++++-
 3 files changed, 79 insertions(+), 16 deletions(-)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/0d47c594fde0de2008b2f26db9ab7a6a22eaf64f


-- 
DragonFly BSD source repository