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[3.16.y-ckt,stable] Patch "proc: Allow creating permanently empty directories that serve as mount points" has been added to staging queue

Message ID 1436779443-22812-1-git-send-email-luis.henriques@canonical.com
State New
Headers show

Commit Message

Luis Henriques July 13, 2015, 9:24 a.m. UTC 
This is a note to let you know that I have just added a patch titled

    proc: Allow creating permanently empty directories that serve as mount points

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt15.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

From 2aa621730024e7811b1ad081ef87c81d43f46cf4 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederm@xmission.com>
Date: Mon, 11 May 2015 16:44:25 -0500
Subject: proc: Allow creating permanently empty directories that serve as
 mount points

commit eb6d38d5427b3ad42f5268da0f1dd31bb0af1264 upstream.

Add a new function proc_create_mount_point that when used to creates a
directory that can not be added to.

Add a new function is_empty_pde to test if a function is a mount
point.

Update the code to use make_empty_dir_inode when reporting
a permanently empty directory to the vfs.

Update the code to not allow adding to permanently empty directories.

Update /proc/openprom and /proc/fs/nfsd to be permanently empty directories.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 fs/proc/generic.c  | 24 ++++++++++++++++++++++++
 fs/proc/inode.c    |  4 ++++
 fs/proc/internal.h |  6 ++++++
 fs/proc/root.c     |  4 ++--
 4 files changed, 36 insertions(+), 2 deletions(-)
diff mbox

Patch

diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index 2e2d9d5d78d9..c18d9b05cea9 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -334,6 +334,11 @@  static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,

 	len = strlen(fn);

+	if (is_empty_pde(*parent)) {
+		WARN(1, "attempt to add to permanently empty directory");
+		return NULL;
+	}
+
 	ent = kzalloc(sizeof(struct proc_dir_entry) + len + 1, GFP_KERNEL);
 	if (!ent)
 		goto out;
@@ -409,6 +414,25 @@  struct proc_dir_entry *proc_mkdir(const char *name,
 }
 EXPORT_SYMBOL(proc_mkdir);

+struct proc_dir_entry *proc_create_mount_point(const char *name)
+{
+	umode_t mode = S_IFDIR | S_IRUGO | S_IXUGO;
+	struct proc_dir_entry *ent, *parent = NULL;
+
+	ent = __proc_create(&parent, name, mode, 2);
+	if (ent) {
+		ent->data = NULL;
+		ent->proc_fops = NULL;
+		ent->proc_iops = NULL;
+		if (proc_register(parent, ent) < 0) {
+			kfree(ent);
+			parent->nlink--;
+			ent = NULL;
+		}
+	}
+	return ent;
+}
+
 struct proc_dir_entry *proc_create_data(const char *name, umode_t mode,
 					struct proc_dir_entry *parent,
 					const struct file_operations *proc_fops,
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 965b82e61570..6582583201ee 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -431,6 +431,10 @@  struct inode *proc_get_inode(struct super_block *sb, struct proc_dir_entry *de)
 		inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 		PROC_I(inode)->pde = de;

+		if (is_empty_pde(de)) {
+			make_empty_dir_inode(inode);
+			return inode;
+		}
 		if (de->mode) {
 			inode->i_mode = de->mode;
 			inode->i_uid = de->uid;
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index 8b24f3640cd9..e62c247b46cc 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -193,6 +193,12 @@  static inline struct proc_dir_entry *pde_get(struct proc_dir_entry *pde)
 }
 extern void pde_put(struct proc_dir_entry *);

+static inline bool is_empty_pde(const struct proc_dir_entry *pde)
+{
+	return S_ISDIR(pde->mode) && !pde->proc_iops;
+}
+struct proc_dir_entry *proc_create_mount_point(const char *name);
+
 /*
  * inode.c
  */
diff --git a/fs/proc/root.c b/fs/proc/root.c
index 7fd8c1f1b1d9..dd77e1483196 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -176,10 +176,10 @@  void __init proc_root_init(void)
 #endif
 	proc_mkdir("fs", NULL);
 	proc_mkdir("driver", NULL);
-	proc_mkdir("fs/nfsd", NULL); /* somewhere for the nfsd filesystem to be mounted */
+	proc_create_mount_point("fs/nfsd"); /* somewhere for the nfsd filesystem to be mounted */
 #if defined(CONFIG_SUN_OPENPROMFS) || defined(CONFIG_SUN_OPENPROMFS_MODULE)
 	/* just give it a mountpoint */
-	proc_mkdir("openprom", NULL);
+	proc_create_mount_point("openprom");
 #endif
 	proc_tty_init();
 	proc_mkdir("bus", NULL);