ASoC: pcm: Fix possible buffer overflow in dpcm state sysfs output

commit 6c89ffea60aa3b2a33ae7987de1e84bfb89e4c9e upstream.

dpcm_show_state() invokes multiple snprintf() calls to concatenate
formatted strings on the fixed size buffer.  The usage of snprintf()
is supposed for avoiding the buffer overflow, but it doesn't work as
expected because snprintf() doesn't return the actual output size but
the size to be written.

Fix this bug by replacing all snprintf() calls with scnprintf()
calls.

Fixes: f86dcef87b77 ("ASoC: dpcm: Add debugFS support for DPCM")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Acked-by: Cezary Rojewski <cezary.rojewski@intel.com>
Link: https://lore.kernel.org/r/20200218111737.14193-4-tiwai@suse.de
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c
index 280bb5cab87fd57f4236d6206fae94973d43d8f1..9df0c8102dc0355ba179834870ffc4aeb16abfcd 100644 (file)
--- a/sound/soc/soc-pcm.c
+++ b/sound/soc/soc-pcm.c
@@ -2979,16 +2979,16 @@ static ssize_t dpcm_show_state(struct snd_soc_pcm_runtime *fe,
        ssize_t offset = 0;
 
        /* FE state */
-       offset += snprintf(buf + offset, size - offset,
+       offset += scnprintf(buf + offset, size - offset,
                        "[%s - %s]\n", fe->dai_link->name,
                        stream ? "Capture" : "Playback");
 
-       offset += snprintf(buf + offset, size - offset, "State: %s\n",
+       offset += scnprintf(buf + offset, size - offset, "State: %s\n",
                        dpcm_state_string(fe->dpcm[stream].state));
 
        if ((fe->dpcm[stream].state >= SND_SOC_DPCM_STATE_HW_PARAMS) &&
            (fe->dpcm[stream].state <= SND_SOC_DPCM_STATE_STOP))
-               offset += snprintf(buf + offset, size - offset,
+               offset += scnprintf(buf + offset, size - offset,
                                "Hardware Params: "
                                "Format = %s, Channels = %d, Rate = %d\n",
                                snd_pcm_format_name(params_format(params)),
@@ -2996,10 +2996,10 @@ static ssize_t dpcm_show_state(struct snd_soc_pcm_runtime *fe,
                                params_rate(params));
 
        /* BEs state */
-       offset += snprintf(buf + offset, size - offset, "Backends:\n");
+       offset += scnprintf(buf + offset, size - offset, "Backends:\n");
 
        if (list_empty(&fe->dpcm[stream].be_clients)) {
-               offset += snprintf(buf + offset, size - offset,
+               offset += scnprintf(buf + offset, size - offset,
                                " No active DSP links\n");
                goto out;
        }
@@ -3008,16 +3008,16 @@ static ssize_t dpcm_show_state(struct snd_soc_pcm_runtime *fe,
                struct snd_soc_pcm_runtime *be = dpcm->be;
                params = &dpcm->hw_params;
 
-               offset += snprintf(buf + offset, size - offset,
+               offset += scnprintf(buf + offset, size - offset,
                                "- %s\n", be->dai_link->name);
 
-               offset += snprintf(buf + offset, size - offset,
+               offset += scnprintf(buf + offset, size - offset,
                                "   State: %s\n",
                                dpcm_state_string(be->dpcm[stream].state));
 
                if ((be->dpcm[stream].state >= SND_SOC_DPCM_STATE_HW_PARAMS) &&
                    (be->dpcm[stream].state <= SND_SOC_DPCM_STATE_STOP))
-                       offset += snprintf(buf + offset, size - offset,
+                       offset += scnprintf(buf + offset, size - offset,
                                "   Hardware Params: "
                                "Format = %s, Channels = %d, Rate = %d\n",
                                snd_pcm_format_name(params_format(params)),