[PATCH] ASoC: cs-amp-lib: Prevent NULL pointer if efi variable is zero length

[Richard Fitzgerald <rf@opensource.cirrus.com>]

In cs_amp_alloc_get_efi_variable() the first call to
cs_amp_get_efi_variable() might return EFI_SUCCESS if the variable
exists with zero length. Trap this and return -ENOENT to prevent
returning an unexpected NULL pointer.

The first cs_amp_get_efi_variable() call was assumed to return
EFI_BUFFER_TOO_SMALL if the variable existed, but if instead it
returned EFI_SUCCESS this would be converted to 0 by
cs_amp_convert_efi_status() and then be returned as a NULL pointer.

Fixes: 00fd40bc7acec ("ASoC: cs-amp-lib: Support Dell SSIDExV2 UEFI variable")
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
---
 sound/soc/codecs/cs-amp-lib.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/sound/soc/codecs/cs-amp-lib.c b/sound/soc/codecs/cs-amp-lib.c
index 41a9a5b005c63..9bc19d2e16394 100644
--- a/sound/soc/codecs/cs-amp-lib.c
+++ b/sound/soc/codecs/cs-amp-lib.c
@@ -317,6 +317,8 @@ static void *cs_amp_alloc_get_efi_variable(efi_char16_t *name,
 	unsigned long size = 0;
 
 	status = cs_amp_get_efi_variable(name, guid, NULL, &size, NULL);
+	if (status == EFI_SUCCESS)
+		return ERR_PTR(-ENOENT);
 	if (status != EFI_BUFFER_TOO_SMALL)
 		return ERR_PTR(cs_amp_convert_efi_status(status));
 
-- 
2.47.3