[PATCH 4.12 38/99] ALSA: core: Fix unexpected error at replacing user TLV

Greg Kroah-Hartman
2017-08-28T08:09:01Z

From: Takashi Iwai <tiwai@suse.de>

commit 88c54cdf61f508ebcf8da2d819f5dfc03e954d1d upstream.

When user tries to replace the user-defined control TLV, the kernel
checks the change of its content via memcmp(). The problem is that
the kernel passes the return value from memcmp() as is. memcmp()
gives a non-zero negative value depending on the comparison result,
and this shall be recognized as an error code.

The patch covers that corner-case, return 1 properly for the changed
TLV.

Fixes: 8aa9b586e420 ("[ALSA] Control API - more robust TLV implementation")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
sound/core/control.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -1157,7 +1157,7 @@ static int snd_ctl_elem_user_tlv(struct
mutex_lock(&ue->card->user_ctl_lock);
change = ue->tlv_data_size != size;
if (!change)
- change = memcmp(ue->tlv_data, new_data, size);
+ change = memcmp(ue->tlv_data, new_data, size) != 0;
kfree(ue->tlv_data);
ue->tlv_data = new_data;
ue->tlv_data_size = size;