proc: reject "." and ".." as filenames

Various subsystems can create files and directories in /proc with names
directly controlled by userspace.

Which means "/", "." and ".." are no-no.

"/" split is already taken care of, do the other 2 prohibited names.

Link: http://lkml.kernel.org/r/20180310001223.GB12443@avx2
Signed-off-by: Alexey Dobriyan <[email protected]>
Acked-by: Florian Westphal <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Cong Wang <[email protected]>
Cc: Pavel Machek <[email protected]>
Cc: Al Viro <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
(cherry picked from commit 7f8cc1a157e6d08dcca856132fd4eff08575bff5)
(cherry picked from commit 4cc3e492c9340edbf047d260fd266604b04efa1a)
(cherry picked from commit 1b0eeeda6bd7338f93d987aac6f9d0097d4c1d8b)
(cherry picked from commit 5a29fc991a481f5e27efd69aad44b1ef87d23f71)
(cherry picked from commit a742d9f9152b2ecedb2b9a589741274a0d1edfc1)
(cherry picked from commit 9b2e763d3140589ebd20fa3530fc92939fa28bfa)
(cherry picked from commit 6ae3968d74f6b0638e89444f7c208bfa2db1d06e)
(cherry picked from commit 191963b41b5246453f240c38a881618937641178)

fs/proc/generic.c

@@ -369,6 +369,14 @@ static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,
 		WARN(1, "name len %u\n", qstr.len);
 		return NULL;
 	}
+	if (qstr.len == 1 && fn[0] == '.') {
+		WARN(1, "name '.'\n");
+		return NULL;
+	}
+	if (qstr.len == 2 && fn[0] == '.' && fn[1] == '.') {
+		WARN(1, "name '..'\n");
+		return NULL;
+	}
 	if (*parent == &proc_root && name_to_int(&qstr) != ~0U) {
 		WARN(1, "create '/proc/%s' by hand\n", qstr.name);
 		return NULL;