ptp: Add a upper bound on max_vclocks

syzbot reported WARNING in max_vclocks_store.

This occurs when the argument max is too large for kcalloc to handle.

Extend the guard to guard against values that are too large for
kcalloc

Reported-by: syzbot+94d20db923b9f51be0df@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=94d20db923b9f51be0df
Tested-by: syzbot+94d20db923b9f51be0df@syzkaller.appspotmail.com
Fixes: 73f3706 ("ptp: support ptp physical/virtual clocks conversion")
Signed-off-by: I Viswanath <viswanathiyyappan@gmail.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Link: https://patch.msgid.link/20250925155908.5034-1-viswanathiyyappan@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: CraftyChimera

drivers/ptp/ptp_private.h

@@ -22,6 +22,7 @@
 #define PTP_MAX_TIMESTAMPS 128
 #define PTP_BUF_TIMESTAMPS 30
 #define PTP_DEFAULT_MAX_VCLOCKS 20
+#define PTP_MAX_VCLOCKS_LIMIT (KMALLOC_MAX_SIZE/(sizeof(int)))
 #define PTP_MAX_CHANNELS 2048
 
 enum {

drivers/ptp/ptp_sysfs.c

@@ -284,7 +284,7 @@ static ssize_t max_vclocks_store(struct device *dev,
 	size_t size;
 	u32 max;
 
-	if (kstrtou32(buf, 0, &max) || max == 0)
+	if (kstrtou32(buf, 0, &max) || max == 0 || max > PTP_MAX_VCLOCKS_LIMIT)
 		return -EINVAL;
 
 	if (max == ptp->max_vclocks)