vc_screen: modify vcs_size() handling in vcs_read()

jira VULN-8820
cve-bf CVE-2023-3567
commit-author George Kennedy <[email protected]>
commit 46d733d

Restore the vcs_size() handling in vcs_read() to what
it had been in previous version.

Fixes: 226fae1 ("vc_screen: move load of struct vc_data pointer in vcs_read() to avoid UAF")
	Suggested-by: Jiri Slaby <[email protected]>
	Signed-off-by: George Kennedy <[email protected]>
	Signed-off-by: Linus Torvalds <[email protected]>
(cherry picked from commit 46d733d)
	Signed-off-by: Shreeya Patel <[email protected]>

Author: shreeya-patel98

drivers/tty/vt/vc_screen.c

@@ -415,10 +415,8 @@ vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 		 */
 		size = vcs_size(vc, attr, uni_mode);
 		if (size < 0) {
-			if (read)
-				break;
 			ret = size;
-			goto unlock_out;
+			break;
 		}
 		if (pos >= size)
 			break;