[PATCH AUTOSEL 4.19 20/21] ALSA: gus: fix null pointer dereference on pointer block

[Sasha Levin]

From: Chengfeng Ye <cyeaa@xxxxxxxxxxxxxx>

[ Upstream commit a0d21bb3279476c777434c40d969ea88ca64f9aa ]

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@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20211024104611.9919-1-cyeaa@xxxxxxxxxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 sound/isa/gus/gus_dma.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/sound/isa/gus/gus_dma.c b/sound/isa/gus/gus_dma.c
index 7f95f452f1064..48e76b8fede41 100644
--- a/sound/isa/gus/gus_dma.c
+++ b/sound/isa/gus/gus_dma.c
@@ -141,6 +141,8 @@ 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
-- 
2.33.0