paride: Fixed integer overflow in pt_read and pt_write

In pt_read() and pt_write(), the "size_t count" variable is assigned to the "int n" variable and then size check is performed.

static ssize_t pt_write(struct file *filp, const char __user *buf, size_t count, loff_t * ppos)

{
	...
        int k, n, r, p, s, t, b;

	...

        while (count > 0) {

                if (!pt_poll_dsc(tape, HZ / 100, PT_TMO, "write"))
                        return -EIO;

                n = count;
                if (n > 32768)
                        n = 32768;      /* max per command */

If the user passes the SIZE_MAX value to the "count" variable, the "n" value is greater than 32768, but it becomes a negative number and passes the size check.
In other words, we need to add a negative check as well, since the size check makes no sense.

---
 drivers/block/paride/pt.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index e815312a00ad..f37aa1349622 100644
@@ -787,7 +787,7 @@ static ssize_t pt_read(struct file *filp, char __user *buf, size_t count, loff_t
 			return -EIO;
 
 		n = count;
-		if (n > 32768)
+		if (n > 32768 || n < 0)
 			n = 32768;	/* max per command */
 		b = (n - 1 + tape->bs) / tape->bs;
 		n = b * tape->bs;	/* rounded up to even block */

@@ -888,7 +888,7 @@ static ssize_t pt_write(struct file *filp, const char __user *buf, size_t count,
 			return -EIO;
 
 		n = count;
-		if (n > 32768)
+		if (n > 32768 || n < 0)
 			n = 32768;	/* max per command */
 		b = (n - 1 + tape->bs) / tape->bs;
 		n = b * tape->bs;	/* rounded up to even block */

2.25.1

Dear all,

I submitted this patch a week ago.

Can I get feedback on this patch?

Regards,
Hyunwoo Kim.