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Subject[02/18] debugfs: fix create mutex racy fops and private data
2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
commit d3a3b0adad0865c12e39b712ca89efbd0a3a0dbc upstream.

Setting fops and private data outside of the mutex at debugfs file
creation introduces a race where the files can be opened with the wrong
file operations and private data. It is easy to trigger with a process
waiting on file creation notification.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/debugfs/inode.c | 55 ++++++++++++++++++++++++++++++-----------------------
1 file changed, 32 insertions(+), 23 deletions(-)
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -32,7 +32,9 @@
static struct vfsmount *debugfs_mount;
static int debugfs_mount_count;

-static struct inode *debugfs_get_inode(struct super_block *sb, int mode, dev_t dev)
+static struct inode *debugfs_get_inode(struct super_block *sb, int mode, dev_t dev,
+ void *data, const struct file_operations *fops)
+
{
struct inode *inode = new_inode(sb);

@@ -47,14 +49,18 @@ static struct inode *debugfs_get_inode(s
init_special_inode(inode, mode, dev);
break;
case S_IFREG:
- inode->i_fop = &debugfs_file_operations;
+ inode->i_fop = fops ? fops : &debugfs_file_operations;
+ inode->i_private = data;
break;
case S_IFLNK:
inode->i_op = &debugfs_link_operations;
+ inode->i_fop = fops;
+ inode->i_private = data;
break;
case S_IFDIR:
inode->i_op = &simple_dir_inode_operations;
- inode->i_fop = &simple_dir_operations;
+ inode->i_fop = fops ? fops : &simple_dir_operations;
+ inode->i_private = data;

/* directory inodes start off with i_nlink == 2
* (for "." entry) */
@@ -67,7 +73,8 @@ static struct inode *debugfs_get_inode(s

/* SMP-safe */
static int debugfs_mknod(struct inode *dir, struct dentry *dentry,
- int mode, dev_t dev)
+ int mode, dev_t dev, void *data,
+ const struct file_operations *fops)
{
struct inode *inode;
int error = -EPERM;
@@ -75,7 +82,7 @@ static int debugfs_mknod(struct inode *d
if (dentry->d_inode)
return -EEXIST;

- inode = debugfs_get_inode(dir->i_sb, mode, dev);
+ inode = debugfs_get_inode(dir->i_sb, mode, dev, data, fops);
if (inode) {
d_instantiate(dentry, inode);
dget(dentry);
@@ -84,12 +91,13 @@ static int debugfs_mknod(struct inode *d
return error;
}

-static int debugfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
+static int debugfs_mkdir(struct inode *dir, struct dentry *dentry, int mode,
+ void *data, const struct file_operations *fops)
{
int res;

mode = (mode & (S_IRWXUGO | S_ISVTX)) | S_IFDIR;
- res = debugfs_mknod(dir, dentry, mode, 0);
+ res = debugfs_mknod(dir, dentry, mode, 0, data, fops);
if (!res) {
inc_nlink(dir);
fsnotify_mkdir(dir, dentry);
@@ -97,18 +105,20 @@ static int debugfs_mkdir(struct inode *d
return res;
}

-static int debugfs_link(struct inode *dir, struct dentry *dentry, int mode)
+static int debugfs_link(struct inode *dir, struct dentry *dentry, int mode,
+ void *data, const struct file_operations *fops)
{
mode = (mode & S_IALLUGO) | S_IFLNK;
- return debugfs_mknod(dir, dentry, mode, 0);
+ return debugfs_mknod(dir, dentry, mode, 0, data, fops);
}

-static int debugfs_create(struct inode *dir, struct dentry *dentry, int mode)
+static int debugfs_create(struct inode *dir, struct dentry *dentry, int mode,
+ void *data, const struct file_operations *fops)
{
int res;

mode = (mode & S_IALLUGO) | S_IFREG;
- res = debugfs_mknod(dir, dentry, mode, 0);
+ res = debugfs_mknod(dir, dentry, mode, 0, data, fops);
if (!res)
fsnotify_create(dir, dentry);
return res;
@@ -142,7 +152,9 @@ static struct file_system_type debug_fs_

static int debugfs_create_by_name(const char *name, mode_t mode,
struct dentry *parent,
- struct dentry **dentry)
+ struct dentry **dentry,
+ void *data,
+ const struct file_operations *fops)
{
int error = 0;

@@ -167,13 +179,16 @@ static int debugfs_create_by_name(const
if (!IS_ERR(*dentry)) {
switch (mode & S_IFMT) {
case S_IFDIR:
- error = debugfs_mkdir(parent->d_inode, *dentry, mode);
+ error = debugfs_mkdir(parent->d_inode, *dentry, mode,
+ data, fops);
break;
case S_IFLNK:
- error = debugfs_link(parent->d_inode, *dentry, mode);
+ error = debugfs_link(parent->d_inode, *dentry, mode,
+ data, fops);
break;
default:
- error = debugfs_create(parent->d_inode, *dentry, mode);
+ error = debugfs_create(parent->d_inode, *dentry, mode,
+ data, fops);
break;
}
dput(*dentry);
@@ -224,19 +239,13 @@ struct dentry *debugfs_create_file(const
if (error)
goto exit;

- error = debugfs_create_by_name(name, mode, parent, &dentry);
+ error = debugfs_create_by_name(name, mode, parent, &dentry,
+ data, fops);
if (error) {
dentry = NULL;
simple_release_fs(&debugfs_mount, &debugfs_mount_count);
goto exit;
}
-
- if (dentry->d_inode) {
- if (data)
- dentry->d_inode->i_private = data;
- if (fops)
- dentry->d_inode->i_fop = fops;
- }
exit:
return dentry;
}



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