ALSA: gus: fix null pointer dereference on pointer block

The pointer block return from snd_gf1_dma_next_block could be
null, so there is a potential null pointer dereference issue.
Fix this by adding a null check before dereference.

Signed-off-by: Chengfeng Ye <cyeaa@connect.ust.hk>
Link: https://lore.kernel.org/r/20211024104611.9919-1-cyeaa@connect.ust.hk
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/isa/gus/gus_dma.c b/sound/isa/gus/gus_dma.c
index a1c770d826ddab1d6ed6d2f6c34aadcdf25d2701..6d664dd8dde0b4fe5b54bf3ea35bca454d81d493 100644 (file)
--- a/sound/isa/gus/gus_dma.c
+++ b/sound/isa/gus/gus_dma.c
@@ -126,6 +126,8 @@ static void snd_gf1_dma_interrupt(struct snd_gus_card * gus)
        }
        block = snd_gf1_dma_next_block(gus);
        spin_unlock(&gus->dma_lock);
+       if (!block)
+               return;
        snd_gf1_dma_program(gus, block->addr, block->buf_addr, block->count, (unsigned short) block->cmd);
        kfree(block);
 #if 0