[PATCH] ALSA: PCM: Fix NULL dereference at mmap checks

[Takashi Iwai]

The recent refactoring of mmap handling caused Oops on some devices
that don't use the standard memory allocations.  This patch addresses
it by allowing snd_dma_buffer_mmap() helper to receive the NULL
pointer dmab argument (and return an error appropriately).

Fixes: a202bd1ad86d ("ALSA: core: Move mmap handler into memalloc ops")
Cc: <stable at vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/core/memalloc.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/sound/core/memalloc.c b/sound/core/memalloc.c
index 0145dabda56d..de7e9d2df39d 100644
--- a/sound/core/memalloc.c
+++ b/sound/core/memalloc.c
@@ -183,8 +183,11 @@ EXPORT_SYMBOL_GPL(snd_devm_alloc_dir_pages);
 int snd_dma_buffer_mmap(struct snd_dma_buffer *dmab,
 			struct vm_area_struct *area)
 {
-	const struct snd_malloc_ops *ops = snd_dma_get_ops(dmab);
+	const struct snd_malloc_ops *ops;
 
+	if (!dmab)
+		return -ENOENT;
+	ops = snd_dma_get_ops(dmab);
 	if (ops && ops->mmap)
 		return ops->mmap(dmab, area);
 	else
-- 
2.31.1