linux-hardening - [PATCH] ALSA: lola: Bounds check loop iterator against streams array size

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Date:   Fri, 20 May 2022 09:55:37 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jaroslav Kysela <perex@...ex.cz>
Cc:     Kees Cook <keescook@...omium.org>, Takashi Iwai <tiwai@...e.com>,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: [PATCH] ALSA: lola: Bounds check loop iterator against streams array size

GCC 12 sees that it's technically possible for num_streams to be larger
than ARRAY_SIZE(pcm->streams). Bounds-check the iterator.

../sound/pci/lola/lola_pcm.c: In function 'lola_pcm_update':
../sound/pci/lola/lola_pcm.c:567:64: warning: array subscript [0, 31] is outside array bounds of 'struct lola_stream[16]' [-Warray-bounds]
  567 |                         struct lola_stream *str = &pcm->streams[i];
      |                                                    ~~~~~~~~~~~~^~~
In file included from ../sound/pci/lola/lola_pcm.c:15:
../sound/pci/lola/lola.h:307:28: note: while referencing 'streams'
  307 |         struct lola_stream streams[MAX_STREAM_COUNT];
      |                            ^~~~~~~

Cc: Jaroslav Kysela <perex@...ex.cz>
Cc: Takashi Iwai <tiwai@...e.com>
Cc: alsa-devel@...a-project.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 sound/pci/lola/lola_pcm.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sound/pci/lola/lola_pcm.c b/sound/pci/lola/lola_pcm.c
index 738ec987000a..32193fae978d 100644
--- a/sound/pci/lola/lola_pcm.c
+++ b/sound/pci/lola/lola_pcm.c
@@ -561,8 +561,9 @@ static snd_pcm_uframes_t lola_pcm_pointer(struct snd_pcm_substream *substream)
 void lola_pcm_update(struct lola *chip, struct lola_pcm *pcm, unsigned int bits)
 {
 	int i;
+	u8 num_streams = min_t(u8, pcm->num_streams, ARRAY_SIZE(pcm->streams));
 
-	for (i = 0; bits && i < pcm->num_streams; i++) {
+	for (i = 0; bits && i < num_streams; i++) {
 		if (bits & (1 << i)) {
 			struct lola_stream *str = &pcm->streams[i];
 			if (str->substream && str->running)
-- 
2.32.0