drivers/misc/lkdtm.c: fix missing allocation failure check

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=44691

Reported-by: <rucsoftsec@gmail.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/misc/lkdtm.c

@@ -477,6 +477,8 @@ static ssize_t lkdtm_debugfs_read(struct file *f, char __user *user_buf,
 	int i, n, out;
 
 	buf = (char *)__get_free_page(GFP_KERNEL);
+	if (buf == NULL)
+		return -ENOMEM;
 
 	n = snprintf(buf, PAGE_SIZE, "Available crash types:\n");
 	for (i = 0; i < ARRAY_SIZE(cp_type); i++)