ALSA: pcm: Fix endless loop for XRUN recovery in OSS emulation
The commit02a5d6925c
("ALSA: pcm: Avoid potential races between OSS ioctls and read/write") split the PCM preparation code to a locked version, and it added a sanity check of runtime->oss.prepare flag along with the change. This leaded to an endless loop when the stream gets XRUN: namely, snd_pcm_oss_write3() and co call snd_pcm_oss_prepare() without setting runtime->oss.prepare flag and the loop continues until the PCM state reaches to another one. As the function is supposed to execute the preparation unconditionally, drop the invalid state check there. The bug was triggered by syzkaller. Fixes:02a5d6925c
("ALSA: pcm: Avoid potential races between OSS ioctls and read/write") Reported-by: syzbot+150189c103427d31a053@syzkaller.appspotmail.com Reported-by: syzbot+7e3f31a52646f939c052@syzkaller.appspotmail.com Reported-by: syzbot+4f2016cf5185da7759dc@syzkaller.appspotmail.com Cc: <stable@vger.kernel.org> Signed-off-by: Takashi Iwai <tiwai@suse.de>
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@ -1128,13 +1128,14 @@ static int snd_pcm_oss_get_active_substream(struct snd_pcm_oss_file *pcm_oss_fil
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}
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/* call with params_lock held */
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/* NOTE: this always call PREPARE unconditionally no matter whether
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* runtime->oss.prepare is set or not
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*/
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static int snd_pcm_oss_prepare(struct snd_pcm_substream *substream)
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{
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int err;
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struct snd_pcm_runtime *runtime = substream->runtime;
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if (!runtime->oss.prepare)
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return 0;
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err = snd_pcm_kernel_ioctl(substream, SNDRV_PCM_IOCTL_PREPARE, NULL);
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if (err < 0) {
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pcm_dbg(substream->pcm,
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