iwlwifi: pcie: Fixed integer overflow in iwl_write_to_user_buf

An integer overflow occurs in the iwl_write_to_user_buf() function,
which is called by the iwl_dbgfs_monitor_data_read() function.

static bool iwl_write_to_user_buf(char __user *user_buf, ssize_t count,
void *buf, ssize_t *size, ssize_t *bytes_copied)

{
	int buf_size_left = count - *bytes_copied;

	buf_size_left = buf_size_left - (buf_size_left % sizeof(u32));
	if (*size > buf_size_left)
		*size = buf_size_left;

If the user passes a SIZE_MAX value to the "ssize_t count" parameter,
the ssize_t count parameter is assigned to "int buf_size_left".
Then compare "*size" with "buf_size_left" . Here, "buf_size_left" is a negative number, so "*size" is assigned "buf_size_left" and goes into the third argument of the copy_to_user function, causing a heap overflow.

This is not a security vulnerability because iwl_dbgfs_monitor_data_read() is a debugfs operation with 0400 privileges.

---
 drivers/net/wireless/intel/iwlwifi/pcie/trans.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index bd50f52a1aad..fded5d305b11 100644
@@ -2854,7 +2854,7 @@ static bool iwl_write_to_user_buf(char __user *user_buf, ssize_t count,
 				  void *buf, ssize_t *size,
 				  ssize_t *bytes_copied)
 {
-	int buf_size_left = count - *bytes_copied;
+	ssize_t buf_size_left = count - *bytes_copied;
 
 	buf_size_left = buf_size_left - (buf_size_left % sizeof(u32));
 	if (*size > buf_size_left)

2.25.1

Out of curiosity, how did you find this?

johannes

I found it while analyzing several device drivers as a personal hobby.

I also want to ask you one question.
While analyzing several device drivers, I found several such integer overflow or race condition problems, and made and submitted a patch.

https://marc.info/?l=linux-fbdev&m=165497564701256&w=2
https://www.spinics.net/lists/linux-efi/msg24884.html

However, there is no response whether this patch has been accepted or rejected. In this case, do I have to send an email to the higher level maintainer? Or do I have to wait?

Thanks,
Hyunwoo Kim