[PATCH] autofs4: allow autofs to work outside the initial PID namespace

[Ian Kent <raven@themaw.net>]

From: Sukadev Bhattiprolu <sukadev@us.ibm.com>

This patch enables autofs4 to work in a "container".  oz_pgrp is converted from
pid_t to struct pid and this is stored at mount time based on the "pgrp=" option
or if the option is missing then the current pgrp.

The "pgrp=" option is interpreted in the PID namespace of the current process.
This option is flawed in that it doesn't carry the namespace information, so it
should be deprecated.  AFAICS the autofs daemon always sends the current pgrp,
which is the default anyway.

The oz_pgrp is also set from the AUTOFS_DEV_IOCTL_SETPIPEFD_CMD ioctl.  This
ioctl sets oz_pgrp to the current pgrp.  It is not allowed to change the pid
namespace.

oz_pgrp is used mainly to determine whether the process traversing the autofs
mount tree is the autofs daemon itself or not.  This function now compares the
pid pointers instead of the pid_t values.

One other use of oz_pgrp is in autofs4_show_options.  There is shows the
virtual pid number (i.e. the one that is valid inside the PID namespace of the
calling process)

For debugging printk convert oz_pgrp to the value in the initial pid namespace.

Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Cc: Eric Biederman <ebiederm@xmission.com>
---
 fs/autofs4/autofs_i.h  |    4 ++--
 fs/autofs4/dev-ioctl.c |   16 ++++++++++++++--
 fs/autofs4/inode.c     |   33 +++++++++++++++++++++++++--------
 3 files changed, 41 insertions(+), 12 deletions(-)

diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h
index 3f1128b..16d3288 100644
--- a/fs/autofs4/autofs_i.h
+++ b/fs/autofs4/autofs_i.h
@@ -104,7 +104,7 @@ struct autofs_sb_info {
 	u32 magic;
 	int pipefd;
 	struct file *pipe;
-	pid_t oz_pgrp;
+	struct pid *oz_pgrp;
 	int catatonic;
 	int version;
 	int sub_version;
@@ -139,7 +139,7 @@ static inline struct autofs_info *autofs4_dentry_ino(struct dentry *dentry)
    filesystem without "magic".) */
 
 static inline int autofs4_oz_mode(struct autofs_sb_info *sbi) {
-	return sbi->catatonic || task_pgrp_nr(current) == sbi->oz_pgrp;
+	return sbi->catatonic || task_pgrp(current) == sbi->oz_pgrp;
 }
 
 /* Does a dentry have some pending activity? */
diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c
index 743c7c2..9183821 100644
--- a/fs/autofs4/dev-ioctl.c
+++ b/fs/autofs4/dev-ioctl.c
@@ -346,6 +346,7 @@ static int autofs_dev_ioctl_setpipefd(struct file *fp,
 {
 	int pipefd;
 	int err = 0;
+	struct pid *new_pid = NULL;
 
 	if (param->setpipefd.pipefd == -1)
 		return -EINVAL;
@@ -357,7 +358,17 @@ static int autofs_dev_ioctl_setpipefd(struct file *fp,
 		mutex_unlock(&sbi->wq_mutex);
 		return -EBUSY;
 	} else {
-		struct file *pipe = fget(pipefd);
+		struct file *pipe;
+
+		new_pid = get_task_pid(current, PIDTYPE_PGID);
+
+		if (ns_of_pid(new_pid) != ns_of_pid(sbi->oz_pgrp)) {
+			AUTOFS_WARN("Not allowed to change PID namespace");
+			err = -EINVAL;
+			goto out;
+		}
+
+		pipe = fget(pipefd);
 		if (!pipe) {
 			err = -EBADF;
 			goto out;
@@ -367,12 +378,13 @@ static int autofs_dev_ioctl_setpipefd(struct file *fp,
 			fput(pipe);
 			goto out;
 		}
-		sbi->oz_pgrp = task_pgrp_nr(current);
+		swap(sbi->oz_pgrp, new_pid);
 		sbi->pipefd = pipefd;
 		sbi->pipe = pipe;
 		sbi->catatonic = 0;
 	}
 out:
+	put_pid(new_pid);
 	mutex_unlock(&sbi->wq_mutex);
 	return err;
 }
diff --git a/fs/autofs4/inode.c b/fs/autofs4/inode.c
index b104726..1b045ec 100644
--- a/fs/autofs4/inode.c
+++ b/fs/autofs4/inode.c
@@ -62,6 +62,8 @@ void autofs4_kill_sb(struct super_block *sb)
 	/* Free wait queues, close pipe */
 	autofs4_catatonic_mode(sbi);
 
+	put_pid(sbi->oz_pgrp);
+
 	sb->s_fs_info = NULL;
 	kfree(sbi);
 
@@ -85,7 +87,7 @@ static int autofs4_show_options(struct seq_file *m, struct dentry *root)
 	if (!gid_eq(root_inode->i_gid, GLOBAL_ROOT_GID))
 		seq_printf(m, ",gid=%u",
 			from_kgid_munged(&init_user_ns, root_inode->i_gid));
-	seq_printf(m, ",pgrp=%d", sbi->oz_pgrp);
+	seq_printf(m, ",pgrp=%d", pid_vnr(sbi->oz_pgrp));
 	seq_printf(m, ",timeout=%lu", sbi->exp_timeout/HZ);
 	seq_printf(m, ",minproto=%d", sbi->min_proto);
 	seq_printf(m, ",maxproto=%d", sbi->max_proto);
@@ -129,7 +131,8 @@ static const match_table_t tokens = {
 };
 
 static int parse_options(char *options, int *pipefd, kuid_t *uid, kgid_t *gid,
-		pid_t *pgrp, unsigned int *type, int *minproto, int *maxproto)
+			 int *pgrp, bool *pgrp_set, unsigned int *type,
+			 int *minproto, int *maxproto)
 {
 	char *p;
 	substring_t args[MAX_OPT_ARGS];
@@ -137,7 +140,6 @@ static int parse_options(char *options, int *pipefd, kuid_t *uid, kgid_t *gid,
 
 	*uid = current_uid();
 	*gid = current_gid();
-	*pgrp = task_pgrp_nr(current);
 
 	*minproto = AUTOFS_MIN_PROTO_VERSION;
 	*maxproto = AUTOFS_MAX_PROTO_VERSION;
@@ -176,6 +178,7 @@ static int parse_options(char *options, int *pipefd, kuid_t *uid, kgid_t *gid,
 			if (match_int(args, &option))
 				return 1;
 			*pgrp = option;
+			*pgrp_set = true;
 			break;
 		case Opt_minproto:
 			if (match_int(args, &option))
@@ -211,6 +214,8 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent)
 	int pipefd;
 	struct autofs_sb_info *sbi;
 	struct autofs_info *ino;
+	int pgrp;
+	bool pgrp_set = false;
 
 	sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
 	if (!sbi)
@@ -223,7 +228,7 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent)
 	sbi->pipe = NULL;
 	sbi->catatonic = 1;
 	sbi->exp_timeout = 0;
-	sbi->oz_pgrp = task_pgrp_nr(current);
+	sbi->oz_pgrp = NULL;
 	sbi->sb = s;
 	sbi->version = 0;
 	sbi->sub_version = 0;
@@ -260,12 +265,23 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent)
 
 	/* Can this call block? */
 	if (parse_options(data, &pipefd, &root_inode->i_uid, &root_inode->i_gid,
-				&sbi->oz_pgrp, &sbi->type, &sbi->min_proto,
-				&sbi->max_proto)) {
+			  &pgrp, &pgrp_set, &sbi->type, &sbi->min_proto,
+			  &sbi->max_proto)) {
 		printk("autofs: called with bogus options\n");
 		goto fail_dput;
 	}
 
+	if (pgrp_set) {
+		sbi->oz_pgrp = find_get_pid(pgrp);
+		if (!sbi->oz_pgrp) {
+			pr_warn("autofs: could not find process group %d\n",
+				pgrp);
+			goto fail_dput;
+		}
+	} else {
+		sbi->oz_pgrp = get_task_pid(current, PIDTYPE_PGID);
+	}
+
 	if (autofs_type_trigger(sbi->type))
 		__managed_dentry_set_managed(root);
 
@@ -289,9 +305,9 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent)
 		sbi->version = sbi->max_proto;
 	sbi->sub_version = AUTOFS_PROTO_SUBVERSION;
 
-	DPRINTK("pipe fd = %d, pgrp = %u", pipefd, sbi->oz_pgrp);
+	DPRINTK("pipe fd = %d, pgrp = %u", pipefd, pid_nr(sbi->oz_pgrp));
 	pipe = fget(pipefd);
-	
+
 	if (!pipe) {
 		printk("autofs: could not open pipe file descriptor\n");
 		goto fail_dput;
@@ -321,6 +337,7 @@ fail_dput:
 fail_ino:
 	kfree(ino);
 fail_free:
+	put_pid(sbi->oz_pgrp);
 	kfree(sbi);
 	s->s_fs_info = NULL;
 fail_unlock: