net: Revert "fib_trie: use seq_file_net rather than seq->private"

This reverts commit 30f38d2fdd79f13fc929489f7e6e517b4a4bfe63.

fib_triestat is surrounded by a big lie: while it claims that it's a
seq_file (fib_triestat_seq_open, fib_triestat_seq_show), it isn't:

static const struct file_operations fib_triestat_fops = {
.owner = THIS_MODULE,
.open = fib_triestat_seq_open,
.read = seq_read,
.llseek = seq_lseek,
.release = single_release_net,
};

Yes, fib_triestat is just a regular file.

A small detail (assuming CONFIG_NET_NS=y) is that while for seq_files
you could do seq_file_net() to get the net ptr, doing so for a regular
file would be wrong and would dereference an invalid pointer.

The fib_triestat lie claimed a victim, and trying to show the file would
be bad for the kernel. This patch just reverts the issue and fixes
fib_triestat, which still needs a rewrite to either be a seq_file or
stop claiming it is.

Signed-off-by: Sasha Levin <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv4/fib_trie.c

···
 
 static int fib_triestat_seq_show(struct seq_file *seq, void *v)
 {
-	struct net *net = seq_file_net(seq);
+	struct net *net = (struct net *)seq->private;
 	unsigned int h;
 
 	seq_printf(seq,