[PATCH 4.8 01/92] ALSA: info: Return error for invalid read/write

[Greg Kroah-Hartman]

4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@xxxxxxx>

commit 6809cd682b82dfff47943850d1a8c714f971b5ca upstream.

Currently the ALSA proc handler allows read or write even if the proc
file were write-only or read-only.  It's mostly harmless, does thing
but allocating memory and ignores the input/output.  But it doesn't
tell user about the invalid use, and it's confusing and inconsistent
in comparison with other proc files.

This patch adds some sanity checks and let the proc handler returning
an -EIO error when the invalid read/write is performed.

Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 sound/core/info.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/sound/core/info.c
+++ b/sound/core/info.c
@@ -325,6 +325,8 @@ static ssize_t snd_info_text_entry_write
 	size_t next;
 	int err = 0;
 
+	if (!entry->c.text.write)
+		return -EIO;
 	pos = *offset;
 	if (!valid_pos(pos, count))
 		return -EIO;
@@ -366,7 +368,9 @@ static int snd_info_seq_show(struct seq_
 	struct snd_info_private_data *data = seq->private;
 	struct snd_info_entry *entry = data->entry;
 
-	if (entry->c.text.read) {
+	if (!entry->c.text.read) {
+		return -EIO;
+	} else {
 		data->rbuffer->buffer = (char *)seq; /* XXX hack! */
 		entry->c.text.read(entry, data->rbuffer);
 	}