proc: proc_pid_ns takes super_block as an argument

syzbot found that

  touch /proc/testfile

causes NULL pointer dereference at tomoyo_get_local_path()
because inode of the dentry is NULL.

Before c59f415a7c, Tomoyo received pid_ns from proc's s_fs_info
directly. Since proc_pid_ns() can only work with inode, using it in
the tomoyo_get_local_path() was wrong.

To avoid creating more functions for getting proc_ns, change the
argument type of the proc_pid_ns() function. Then, Tomoyo can use
the existing super_block to get pid_ns.

Link: https://lkml.kernel.org/r/0000000000002f0c7505a5b0e04c@google.com
Link: https://lkml.kernel.org/r/20200518180738.2939611-1-gladkov.alexey@gmail.com
Reported-by: syzbot+c1af344512918c61362c@syzkaller.appspotmail.com
Fixes: c59f415a7c ("Use proc_pid_ns() to get pid_namespace from the proc superblock")
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 = proc_pid_ns(file_inode(f->file));
+	struct pid_namespace *proc_pidns = proc_pid_ns(file_inode(f->file)->i_sb);
 
 	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 = proc_pid_ns(file_inode(f->file));
+	struct pid_namespace *proc_pidns = proc_pid_ns(file_inode(f->file)->i_sb);
 
 	fl = hlist_entry(v, struct file_lock, fl_link);
 

fs/proc/array.c

@@ -728,7 +728,7 @@ static int children_seq_show(struct seq_file *seq, void *v)
 {
 	struct inode *inode = file_inode(seq->file);
 
-	seq_printf(seq, "%d ", pid_nr_ns(v, proc_pid_ns(inode)));
+	seq_printf(seq, "%d ", pid_nr_ns(v, proc_pid_ns(inode->i_sb)));
 	return 0;
 }
 

fs/proc/base.c

@@ -754,7 +754,7 @@ static const struct inode_operations proc_def_inode_operations = {
 static int proc_single_show(struct seq_file *m, void *v)
 {
 	struct inode *inode = m->private;
-	struct pid_namespace *ns = proc_pid_ns(inode);
+	struct pid_namespace *ns = proc_pid_ns(inode->i_sb);
 	struct pid *pid = proc_pid(inode);
 	struct task_struct *task;
 	int ret;
@@ -1423,7 +1423,7 @@ static const struct file_operations proc_fail_nth_operations = {
 static int sched_show(struct seq_file *m, void *v)
 {
 	struct inode *inode = m->private;
-	struct pid_namespace *ns = proc_pid_ns(inode);
+	struct pid_namespace *ns = proc_pid_ns(inode->i_sb);
 	struct task_struct *p;
 
 	p = get_proc_task(inode);
@@ -2466,7 +2466,7 @@ static int proc_timers_open(struct inode *inode, struct file *file)
 		return -ENOMEM;
 
 	tp->pid = proc_pid(inode);
-	tp->ns = proc_pid_ns(inode);
+	tp->ns = proc_pid_ns(inode->i_sb);
 	return 0;
 }
 
@@ -3377,7 +3377,7 @@ int proc_pid_readdir(struct file *file, struct dir_context *ctx)
 {
 	struct tgid_iter iter;
 	struct proc_fs_info *fs_info = proc_sb_info(file_inode(file)->i_sb);
-	struct pid_namespace *ns = proc_pid_ns(file_inode(file));
+	struct pid_namespace *ns = proc_pid_ns(file_inode(file)->i_sb);
 	loff_t pos = ctx->pos;
 
 	if (pos >= PID_MAX_LIMIT + TGID_OFFSET)
@@ -3730,7 +3730,7 @@ static int proc_task_readdir(struct file *file, struct dir_context *ctx)
 	/* f_version caches the tgid value that the last readdir call couldn't
 	 * return. lseek aka telldir automagically resets f_version to 0.
 	 */
-	ns = proc_pid_ns(inode);
+	ns = proc_pid_ns(inode->i_sb);
 	tid = (int)file->f_version;
 	file->f_version = 0;
 	for (task = first_tid(proc_pid(inode), tid, ctx->pos - 2, ns);

fs/proc/self.c

@@ -12,7 +12,7 @@ static const char *proc_self_get_link(struct dentry *dentry,
 				      struct inode *inode,
 				      struct delayed_call *done)
 {
-	struct pid_namespace *ns = proc_pid_ns(inode);
+	struct pid_namespace *ns = proc_pid_ns(inode->i_sb);
 	pid_t tgid = task_tgid_nr_ns(current, ns);
 	char *name;
 

fs/proc/thread_self.c

@@ -12,7 +12,7 @@ static const char *proc_thread_self_get_link(struct dentry *dentry,
 					     struct inode *inode,
 					     struct delayed_call *done)
 {
-	struct pid_namespace *ns = proc_pid_ns(inode);
+	struct pid_namespace *ns = proc_pid_ns(inode->i_sb);
 	pid_t tgid = task_tgid_nr_ns(current, ns);
 	pid_t pid = task_pid_nr_ns(current, ns);
 	char *name;

include/linux/proc_fs.h

@@ -202,9 +202,9 @@ int open_related_ns(struct ns_common *ns,
 		   struct ns_common *(*get_ns)(struct ns_common *ns));
 
 /* get the associated pid namespace for a file in procfs */
-static inline struct pid_namespace *proc_pid_ns(const struct inode *inode)
+static inline struct pid_namespace *proc_pid_ns(struct super_block *sb)
 {
-	return proc_sb_info(inode->i_sb)->pid_ns;
+	return proc_sb_info(sb)->pid_ns;
 }
 
 #endif /* _LINUX_PROC_FS_H */

kernel/fork.c

@@ -1745,7 +1745,7 @@ static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
 	pid_t nr = -1;
 
 	if (likely(pid_has_task(pid, PIDTYPE_PID))) {
-		ns = proc_pid_ns(file_inode(m->file));
+		ns = proc_pid_ns(file_inode(m->file)->i_sb);
 		nr = pid_nr_ns(pid, ns);
 	}
 

net/ipv6/ip6_flowlabel.c

@@ -779,7 +779,7 @@ static void *ip6fl_seq_start(struct seq_file *seq, loff_t *pos)
 {
 	struct ip6fl_iter_state *state = ip6fl_seq_private(seq);
 
-	state->pid_ns = proc_pid_ns(file_inode(seq->file));
+	state->pid_ns = proc_pid_ns(file_inode(seq->file)->i_sb);
 
 	rcu_read_lock_bh();
 	return *pos ? ip6fl_get_idx(seq, *pos - 1) : SEQ_START_TOKEN;

security/tomoyo/realpath.c

@@ -162,7 +162,7 @@ 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));
+		struct pid_namespace *proc_pidns = proc_pid_ns(sb);
 
 		if (*ep == '/' && pid && pid ==
 		    task_tgid_nr_ns(current, proc_pidns)) {