ALSA: info: Check for integer overflow in snd_info_entry_write()

snd_info_entry_write() resizes the buffer with an unsigned long
size argument that gets truncated because resize_info_buffer()
takes the size parameter as an unsigned int. On 64-bit kernels,
this causes the following copy_to_user() to write out-of-bounds
if (pos + count) can't be represented by an unsigned int.

Bug: 32510733
Change-Id: I9e8b55f93f2bd606b4a73b5a4525b71ee88c7c23
Signed-off-by: Siqi Lin <siqilin@google.com>
Git-repo: https://android.googlesource.com/kernel/msm
Git-commit: 600c59f1f58bf30716d4a072add85f8da77c145c
Signed-off-by: Dennis Cagle <d-cagle@codeaurora.org>

sound/core/info.c

@@ -260,6 +260,7 @@ static ssize_t snd_info_entry_write(struct file *file, const char __user *buffer
 	struct snd_info_buffer *buf;
 	ssize_t size = 0;
 	loff_t pos;
+	unsigned long realloc_size;
 
 	data = file->private_data;
 	if (snd_BUG_ON(!data))
@@ -268,7 +269,8 @@ static ssize_t snd_info_entry_write(struct file *file, const char __user *buffer
 	pos = *offset;
 	if (pos < 0 || (long) pos != pos || (ssize_t) count < 0)
 		return -EIO;
-	if ((unsigned long) pos + (unsigned long) count < (unsigned long) pos)
+	realloc_size = (unsigned long) pos + (unsigned long) count;
+	if (realloc_size < (unsigned long) pos || realloc_size > UINT_MAX)
 		return -EIO;
 	switch (entry->content) {
 	case SNDRV_INFO_CONTENT_TEXT: