Use proc_pid_ns() to get pid_namespace from the proc superblock

To get pid_namespace from the procfs superblock should be used a special
helper. This will avoid errors when s_fs_info will change the type.

Link: https://lore.kernel.org/lkml/20200423200316.164518-3-gladkov.alexey@gmail.com/
Link: https://lore.kernel.org/lkml/20200423112858.95820-1-gladkov.alexey@gmail.com/
Link: https://lore.kernel.org/lkml/06B50A1C-406F-4057-BFA8-3A7729EA7469@lca.pw/
Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

fs/locks.c

@@ -2823,7 +2823,7 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
 {
 	struct inode *inode = NULL;
 	unsigned int fl_pid;
-	struct pid_namespace *proc_pidns = file_inode(f->file)->i_sb->s_fs_info;
+	struct pid_namespace *proc_pidns = proc_pid_ns(file_inode(f->file));
 
 	fl_pid = locks_translate_pid(fl, proc_pidns);
 	/*
@@ -2901,7 +2901,7 @@ static int locks_show(struct seq_file *f, void *v)
 {
 	struct locks_iterator *iter = f->private;
 	struct file_lock *fl, *bfl;
-	struct pid_namespace *proc_pidns = file_inode(f->file)->i_sb->s_fs_info;
+	struct pid_namespace *proc_pidns = proc_pid_ns(file_inode(f->file));
 
 	fl = hlist_entry(v, struct file_lock, fl_link);
 

security/tomoyo/realpath.c

@@ -7,6 +7,7 @@
 
 #include "common.h"
 #include <linux/magic.h>
+#include <linux/proc_fs.h>
 
 /**
  * tomoyo_encode2 - Encode binary string to ascii string.
@@ -161,9 +162,10 @@ static char *tomoyo_get_local_path(struct dentry *dentry, char * const buffer,
 	if (sb->s_magic == PROC_SUPER_MAGIC && *pos == '/') {
 		char *ep;
 		const pid_t pid = (pid_t) simple_strtoul(pos + 1, &ep, 10);
+		struct pid_namespace *proc_pidns = proc_pid_ns(d_inode(dentry));
 
 		if (*ep == '/' && pid && pid ==
-		    task_tgid_nr_ns(current, sb->s_fs_info)) {
+		    task_tgid_nr_ns(current, proc_pidns)) {
 			pos = ep - 5;
 			if (pos < buffer)
 				goto out;