cvs commit: src/sys/dev/sound/pcm sound.c sound.h vchan.c

Ariff Abdullah ariff at
Thu Mar 16 04:12:50 UTC 2006

ariff       2006-03-16 04:12:49 UTC

  FreeBSD src repository

  Modified files:
    sys/dev/sound/pcm    sound.c sound.h vchan.c 
  Fix severe 8bit integer overflow during channel creation and destruction,
  especially for vchans. It turns out that channel numbering always depend
  on d->devcount counter (which keep increasing), while PCMMKMINOR() truncate
  everything to 8bit length. At some point the truncation cause the newly
  created character device overlapped with the existence one, causing erratic
  overall system behaviour and panic. Easily reproduce with something like:
          (Luckily, only root can reproduce this)
          while : ; do
                  sysctl hw.snd.pcm0.vchans=200
                  sysctl hw.snd.pcm0.vchans=100
  - Enforce channel/chardev numbering within 8bit boundary. Return E2BIG
    if necessary.
  - Traverse d->channels SLIST and try to reclaim "free" counter during channel
    creation. Don't rely on d->devcount at all.
  - Destroy vchans in reverse order.
  Anyway, this is not the fault of vchans. It is just that vchans are so cute
  and begging to be abused ;) . Don't blame her.
  Old, hidden bugs.. sigh..
  MFC after:      3 days
  Revision  Changes    Path
  1.99      +73 -32    src/sys/dev/sound/pcm/sound.c
  1.67      +11 -6     src/sys/dev/sound/pcm/sound.h
  1.23      +15 -6     src/sys/dev/sound/pcm/vchan.c

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