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Date:      Thu, 16 May 2019 12:34:43 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 237924] Possible infinite loop in function empty_aux_buffer of sys/dev/atkbdc/atkbdc.c
Message-ID:  <bug-237924-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=237924

            Bug ID: 237924
           Summary: Possible infinite loop in function empty_aux_buffer of
                    sys/dev/atkbdc/atkbdc.c
           Product: Base System
           Version: CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Many People
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: yangx92@hotmail.com

Created attachment 204401
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=204401&action=edit
Proposed patch

There is a possible infinite loop vulnerability in function empty_aux_buffer of 
sys/dev/atkbdc/atkbdc.c

Some systems (Intel/IBM blades) do not have keyboard devices and will thus hang
in the processure.

void
empty_aux_buffer(KBDC p, int wait)
{
    int t;
    int b;
    int f;
#if KBDIO_DEBUG >= 2
    int c1 = 0;
    int c2 = 0;
#endif
    int delta = 2;

    for (t = wait; t > 0; ) {
        if ((f = read_status(kbdcp(p))) & KBDS_ANY_BUFFER_FULL) {
            DELAY(KBDD_DELAYTIME);
            b = read_data(kbdcp(p));
            if ((f & KBDS_BUFFER_FULL) == KBDS_KBD_BUFFER_FULL) {
                addq(&kbdcp(p)->kbd, b);
#if KBDIO_DEBUG >= 2
                ++c1;
            } else {
                ++c2;
#endif
            }
            t = wait;
        } else {
            t -= delta;
        }
        DELAY(delta*1000);
    }
#if KBDIO_DEBUG >= 2
    if ((c1 > 0) || (c2 > 0))
        log(LOG_DEBUG, "kbdc: %d:%d char read (empty_aux_buffer)\n", c1, c2);
#endif

    emptyq(&kbdcp(p)->aux);
}

The attachment is the proposed patch that are copied from
https://github.com/freebsd/freebsd/commit/3631541670c84a8731b46350daa30502edb0ca80

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