netdevsim: prevent bad user input in nsim_dev_health_break_write()

If either a zero count or a large one is provided, kernel can crash.

Fixes: 82c93a87bf ("netdevsim: implement couple of testing devlink health reporters")
Reported-by: [email protected]
Closes: https://lore.kernel.org/netdev/[email protected]/T/#u
Signed-off-by: Eric Dumazet <[email protected]>
Cc: Jiri Pirko <[email protected]>
Reviewed-by: Joe Damato <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

drivers/net/netdevsim/health.c

@@ -149,6 +149,8 @@ static ssize_t nsim_dev_health_break_write(struct file *file,
 	char *break_msg;
 	int err;
 
+	if (count == 0 || count > PAGE_SIZE)
+		return -EINVAL;
 	break_msg = memdup_user_nul(data, count);
 	if (IS_ERR(break_msg))
 		return PTR_ERR(break_msg);