3.2.89-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Takashi Iwai <tiwai@xxxxxxx> commit f3ac9f737603da80c2da3e84b89e74429836bb6d upstream. The sequencer FIFO management has a bug that may lead to a corruption (shortage) of the cell linked list. When a sequencer client faces an error at the event delivery, it tries to put back the dequeued cell. When the first queue was put back, this forgot the tail pointer tracking, and the link will be screwed up. Although there is no memory corruption, the sequencer client may stall forever at exit while flushing the pending FIFO cells in snd_seq_pool_done(), as spotted by syzkaller. This patch addresses the missing tail pointer tracking at snd_seq_fifo_cell_putback(). Also the patch makes sure to clear the cell->enxt pointer at snd_seq_fifo_event_in() for avoiding a similar mess-up of the FIFO linked list. Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Signed-off-by: Takashi Iwai <tiwai@xxxxxxx> Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> --- sound/core/seq/seq_fifo.c | 3 +++ 1 file changed, 3 insertions(+) --- a/sound/core/seq/seq_fifo.c +++ b/sound/core/seq/seq_fifo.c @@ -137,6 +137,7 @@ int snd_seq_fifo_event_in(struct snd_seq f->tail = cell; if (f->head == NULL) f->head = cell; + cell->next = NULL; f->cells++; spin_unlock_irqrestore(&f->lock, flags); @@ -216,6 +217,8 @@ void snd_seq_fifo_cell_putback(struct sn spin_lock_irqsave(&f->lock, flags); cell->next = f->head; f->head = cell; + if (!f->tail) + f->tail = cell; f->cells++; spin_unlock_irqrestore(&f->lock, flags); }