Message-ID: <142d8d23-4feb-a0ed-a1ba-50cb1fa57cd6@linux.ibm.com>
Date:   Thu, 2 Dec 2021 08:47:53 -0500
From:   Stefan Berger <stefanb@...ux.ibm.com>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     linux-integrity@...r.kernel.org, zohar@...ux.ibm.com,
        serge@...lyn.com, containers@...ts.linux.dev,
        dmitry.kasatkin@...il.com, ebiederm@...ssion.com,
        krzysztof.struczynski@...wei.com, roberto.sassu@...wei.com,
        mpeters@...hat.com, lhinds@...hat.com, lsturman@...hat.com,
        puiterwi@...hat.com, jejb@...ux.ibm.com, jamjoom@...ibm.com,
        linux-kernel@...r.kernel.org, paul@...l-moore.com, rgb@...hat.com,
        linux-security-module@...r.kernel.org, jmorris@...ei.org
Subject: Re: [RFC 13/20] securityfs: Build securityfs_ns for namespacing
 support


On 12/2/21 08:35, Christian Brauner wrote:
> On Tue, Nov 30, 2021 at 11:06:47AM -0500, Stefan Berger wrote:
>> Implement 'securityfs_ns' for support of IMA namespacing so that each
>> IMA (user) namespace can have its own front-end for showing the currently
>> active policy, the measurement list, number of violations and so on. This
>> filesystem shares much of the existing code of SecurityFS but requires a
>> new API call securityfs_ns_create_mount() for creating a new instance.
>>
>> The API calls of securityfs_ns have the prefix securityfs_ns_ and take
>> additional parameters struct vfsmount * and mount_count that allow for
>> multiple instances of this filesystem to exist.
>>
>> The filesystem can be mounted to the usual securityfs mount point like
>> this:
>>
>> mount -t securityfs_ns /sys/kernel/security /sys/kernel/security
>>
>> Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>
>> ---
>>   include/linux/security.h   |  18 ++++
>>   include/uapi/linux/magic.h |   1 +
>>   security/inode.c           | 197 +++++++++++++++++++++++++++++++++++--
>>   3 files changed, 210 insertions(+), 6 deletions(-)
>>
>> diff --git a/include/linux/security.h b/include/linux/security.h
>> index 7e0ba63b5dde..8e479266f544 100644
>> --- a/include/linux/security.h
>> +++ b/include/linux/security.h
>> @@ -1929,6 +1929,24 @@ struct dentry *securityfs_create_symlink(const char *name,
>>   					 const struct inode_operations *iops);
>>   extern void securityfs_remove(struct dentry *dentry);
>>   
>> +extern struct dentry *securityfs_ns_create_file(const char *name, umode_t mode,
>> +						struct dentry *parent, void *data,
>> +						const struct file_operations *fops,
>> +						const struct inode_operations *iops,
>> +						struct vfsmount **mount, int *mount_count);
>> +extern struct dentry *securityfs_ns_create_dir(const char *name, struct dentry *parent,
>> +					       const struct inode_operations *iops,
>> +					       struct vfsmount **mount, int *mount_count);
>> +struct dentry *securityfs_ns_create_symlink(const char *name,
>> +					    struct dentry *parent,
>> +					    const char *target,
>> +					    const struct inode_operations *iops,
>> +					    struct vfsmount **mount, int *mount_count);
>> +extern void securityfs_ns_remove(struct dentry *dentry,
>> +				 struct vfsmount **mount, int *mount_count);
>> +struct vfsmount *securityfs_ns_create_mount(struct user_namespace *user_ns);
>> +extern struct vfsmount *securityfs_ns_mount;
>> +
>>   #else /* CONFIG_SECURITYFS */
>>   
>>   static inline struct dentry *securityfs_create_dir(const char *name,
>> diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
>> index 35687dcb1a42..5c1cc6088dd2 100644
>> --- a/include/uapi/linux/magic.h
>> +++ b/include/uapi/linux/magic.h
>> @@ -11,6 +11,7 @@
>>   #define CRAMFS_MAGIC_WEND	0x453dcd28	/* magic number with the wrong endianess */
>>   #define DEBUGFS_MAGIC          0x64626720
>>   #define SECURITYFS_MAGIC	0x73636673
>> +#define SECURITYFS_NS_MAGIC	0x73334473
>>   #define SELINUX_MAGIC		0xf97cff8c
>>   #define SMACK_MAGIC		0x43415d53	/* "SMAC" */
>>   #define RAMFS_MAGIC		0x858458f6	/* some random number */
>> diff --git a/security/inode.c b/security/inode.c
>> index 429744ff4ab3..8077d1f31489 100644
>> --- a/security/inode.c
>> +++ b/security/inode.c
>> @@ -21,6 +21,7 @@
>>   #include <linux/security.h>
>>   #include <linux/lsm_hooks.h>
>>   #include <linux/magic.h>
>> +#include <linux/user_namespace.h>
>>   
>>   static struct vfsmount *securityfs_mount;
>>   static int securityfs_mount_count;
>> @@ -73,6 +74,61 @@ static struct file_system_type securityfs_type = {
>>   	.kill_sb =	kill_litter_super,
>>   };
>>   
>> +static int securityfs_ns_fill_super(struct super_block *sb, struct fs_context *fc)
>> +{
>> +	static const struct tree_descr files[] = {{""}};
>> +	int error;
>> +
>> +	error = simple_fill_super(sb, SECURITYFS_NS_MAGIC, files);
>> +	if (error)
>> +		return error;
>> +
>> +	sb->s_op = &securityfs_super_operations;
>> +
>> +	return 0;
>> +}
>> +
>> +static int securityfs_ns_get_tree(struct fs_context *fc)
>> +{
>> +	return get_tree_keyed(fc, securityfs_ns_fill_super, fc->user_ns);
>> +}
>> +
>> +static const struct fs_context_operations securityfs_ns_context_ops = {
>> +	.get_tree	= securityfs_ns_get_tree,
>> +};
>> +
>> +static int securityfs_ns_init_fs_context(struct fs_context *fc)
>> +{
>> +	fc->ops = &securityfs_ns_context_ops;
>> +	return 0;
>> +}
>> +
>> +static struct file_system_type securityfs_ns_type = {
>> +	.owner			= THIS_MODULE,
>> +	.name			= "securityfs_ns",
>> +	.init_fs_context	= securityfs_ns_init_fs_context,
>> +	.kill_sb		= kill_litter_super,
>> +	.fs_flags		= FS_USERNS_MOUNT,
>> +};
>> +
>> +struct vfsmount *securityfs_ns_create_mount(struct user_namespace *user_ns)
>> +{
>> +	struct fs_context *fc;
>> +	struct vfsmount *mnt;
>> +
>> +	fc = fs_context_for_mount(&securityfs_ns_type, SB_KERNMOUNT);
>> +	if (IS_ERR(fc))
>> +		return ERR_CAST(fc);
>> +
>> +	put_user_ns(fc->user_ns);
>> +	fc->user_ns = get_user_ns(user_ns);
>> +
>> +	mnt = fc_mount(fc);
>> +	put_fs_context(fc);
>> +	return mnt;
>> +}
>> +
>> +
>>   /**
>>    * securityfs_create_dentry - create a dentry in the securityfs filesystem
>>    *
>> @@ -155,8 +211,8 @@ static struct dentry *securityfs_create_dentry(const char *name, umode_t mode,
>>   	inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
>>   	inode->i_private = data;
>>   	if (S_ISDIR(mode)) {
>> -		inode->i_op = &simple_dir_inode_operations;
>> -		inode->i_fop = &simple_dir_operations;
>> +		inode->i_op = iops ? iops : &simple_dir_inode_operations;
>> +		inode->i_fop = fops ? fops : &simple_dir_operations;
>>   		inc_nlink(inode);
>>   		inc_nlink(dir);
>>   	} else if (S_ISLNK(mode)) {
>> @@ -214,6 +270,41 @@ struct dentry *securityfs_create_file(const char *name, umode_t mode,
>>   }
>>   EXPORT_SYMBOL_GPL(securityfs_create_file);
>>   
>> +/**
>> + * securityfs_ns_create_file - create a file in the securityfs_ns filesystem
>> + *
>> + * @name: a pointer to a string containing the name of the file to create.
>> + * @mode: the permission that the file should have
>> + * @parent: a pointer to the parent dentry for this file.  This should be a
>> + *          directory dentry if set.  If this parameter is %NULL, then the
>> + *          file will be created in the root of the securityfs_ns filesystem.
>> + * @data: a pointer to something that the caller will want to get to later
>> + *        on.  The inode.i_private pointer will point to this value on
>> + *        the open() call.
>> + * @fops: a pointer to a struct file_operations that should be used for
>> + *        this file.
>> + * @mount: Pointer to a pointer of a an existing vfsmount
>> + * @mount_count: The mount_count that goes along with the @mount
>> + *
>> + * This function creates a file in securityfs_ns with the given @name.
>> + *
>> + * This function returns a pointer to a dentry if it succeeds.  This
>> + * pointer must be passed to the securityfs_ns_remove() function when the file
>> + * is to be removed (no automatic cleanup happens if your module is unloaded,
>> + * you are responsible here).  If an error occurs, the function will return
>> + * the error value (via ERR_PTR).
>> + */
>> +struct dentry *securityfs_ns_create_file(const char *name, umode_t mode,
>> +					 struct dentry *parent, void *data,
>> +					 const struct file_operations *fops,
>> +					 const struct inode_operations *iops,
>> +					 struct vfsmount **mount, int *mount_count)
>> +{
>> +	return securityfs_create_dentry(name, mode, parent, data, fops, iops,
>> +					&securityfs_ns_type, mount, mount_count);
>> +}
>> +EXPORT_SYMBOL_GPL(securityfs_ns_create_file);
>> +
>>   /**
>>    * securityfs_create_dir - create a directory in the securityfs filesystem
>>    *
>> @@ -240,6 +331,34 @@ struct dentry *securityfs_create_dir(const char *name, struct dentry *parent)
>>   }
>>   EXPORT_SYMBOL_GPL(securityfs_create_dir);
>>   
>> +/**
>> + * securityfs_ns_create_dir - create a directory in the securityfs_ns filesystem
>> + *
>> + * @name: a pointer to a string containing the name of the directory to
>> + *        create.
>> + * @parent: a pointer to the parent dentry for this file.  This should be a
>> + *          directory dentry if set.  If this parameter is %NULL, then the
>> + *          directory will be created in the root of the securityfs_ns filesystem.
>> + * @mount: Pointer to a pointer of a an existing vfsmount
>> + * @mount_count: The mount_count that goes along with the @mount
>> + *
>> + * This function creates a directory in securityfs_ns with the given @name.
>> + *
>> + * This function returns a pointer to a dentry if it succeeds.  This
>> + * pointer must be passed to the securityfs_ns_remove() function when the file
>> + * is to be removed (no automatic cleanup happens if your module is unloaded,
>> + * you are responsible here).  If an error occurs, the function will return
>> + * the error value (via ERR_PTR).
>> + */
>> +struct dentry *securityfs_ns_create_dir(const char *name, struct dentry *parent,
>> +					const struct inode_operations *iops,
>> +					struct vfsmount **mount, int *mount_count)
>> +{
>> +	return securityfs_ns_create_file(name, S_IFDIR | 0755, parent, NULL, NULL,
>> +					 iops, mount, mount_count);
>> +}
>> +EXPORT_SYMBOL_GPL(securityfs_ns_create_dir);
>> +
>>   struct dentry *_securityfs_create_symlink(const char *name,
>>   					  struct dentry *parent,
>>   					  const char *target,
>> @@ -263,6 +382,7 @@ struct dentry *_securityfs_create_symlink(const char *name,
>>   
>>   	return dent;
>>   }
>> +
>>   /**
>>    * securityfs_create_symlink - create a symlink in the securityfs filesystem
>>    *
>> @@ -300,6 +420,42 @@ struct dentry *securityfs_create_symlink(const char *name,
>>   }
>>   EXPORT_SYMBOL_GPL(securityfs_create_symlink);
>>   
>> +/**
>> + * securityfs_ns_create_symlink - create a symlink in the securityfs_ns filesystem
>> + *
>> + * @name: a pointer to a string containing the name of the symlink to
>> + *        create.
>> + * @parent: a pointer to the parent dentry for the symlink.  This should be a
>> + *          directory dentry if set.  If this parameter is %NULL, then the
>> + *          directory will be created in the root of the securityfs_ns filesystem.
>> + * @target: a pointer to a string containing the name of the symlink's target.
>> + *          If this parameter is %NULL, then the @iops parameter needs to be
>> + *          setup to handle .readlink and .get_link inode_operations.
>> + * @iops: a pointer to the struct inode_operations to use for the symlink. If
>> + *        this parameter is %NULL, then the default simple_symlink_inode
>> + *        operations will be used.
>> + * @mount: Pointer to a pointer of a an existing vfsmount
>> + * @mount_count: The mount_count that goes along with the @mount
>> + *
>> + * This function creates a symlink in securityfs_ns with the given @name.
>> + *
>> + * This function returns a pointer to a dentry if it succeeds.  This
>> + * pointer must be passed to the securityfs_ns_remove() function when the file
>> + * is to be removed (no automatic cleanup happens if your module is unloaded,
>> + * you are responsible here).  If an error occurs, the function will return
>> + * the error value (via ERR_PTR).
>> + */
>> +struct dentry *securityfs_ns_create_symlink(const char *name,
>> +					    struct dentry *parent,
>> +					    const char *target,
>> +					    const struct inode_operations *iops,
>> +					    struct vfsmount **mount, int *mount_count)
>> +{
>> +	return _securityfs_create_symlink(name, parent, target, iops,
>> +					  &securityfs_ns_type, mount, mount_count);
>> +}
>> +EXPORT_SYMBOL_GPL(securityfs_ns_create_symlink);
>> +
>>   void _securityfs_remove(struct dentry *dentry, struct vfsmount **mount, int *mount_count)
>>   {
>>   	struct inode *dir;
>> @@ -340,6 +496,27 @@ void securityfs_remove(struct dentry *dentry)
>>   
>>   EXPORT_SYMBOL_GPL(securityfs_remove);
>>   
>> +/**
>> + * securityfs_ns_remove - removes a file or directory from the securityfs_ns filesystem
>> + *
>> + * @dentry: a pointer to a the dentry of the file or directory to be removed.
>> + * @mount: Pointer to a pointer of a an existing vfsmount
>> + * @mount_count: The mount_count that goes along with the @mount
>> + *
>> + * This function removes a file or directory in securityfs_ns that was previously
>> + * created with a call to another securityfs_ns function (like
>> + * securityfs_ns_create_file() or variants thereof.)
>> + *
>> + * This function is required to be called in order for the file to be
>> + * removed. No automatic cleanup of files will happen when a module is
>> + * removed; you are responsible here.
>> + */
>> +void securityfs_ns_remove(struct dentry *dentry, struct vfsmount **mount, int *mount_count)
>> +{
>> +	_securityfs_remove(dentry, mount, mount_count);
>> +}
>> +EXPORT_SYMBOL_GPL(securityfs_ns_remove);
>> +
>>   #ifdef CONFIG_SECURITY
>>   static struct dentry *lsm_dentry;
>>   static ssize_t lsm_read(struct file *filp, char __user *buf, size_t count,
>> @@ -364,14 +541,22 @@ static int __init securityfs_init(void)
>>   		return retval;
>>   
>>   	retval = register_filesystem(&securityfs_type);
>> -	if (retval) {
>> -		sysfs_remove_mount_point(kernel_kobj, "security");
>> -		return retval;
>> -	}
>> +	if (retval)
>> +		goto remove_mount;
>> +	retval = register_filesystem(&securityfs_ns_type);
>> +	if (retval)
>> +		goto unregister_filesystem;
> So you're introducing a new filesystem type securityfs_ns. Ithink that's
> simply wrong and feels like a hack. What issues did you run into when
> trying to convert the existing securityfs itself?

I primarily didn't want to touch the existing securityfs with its 
existing users and it being a single instance filesystem. So I though 
I'd create something with a new API just for namespaces that is 
multi-instance capable.


>
> I see no immediate reason why a get_tree_keyed() conversion for
> securityfs wouldn't work even with the debugfs pin/unpin logic in there
> kept for the securityfs mounted in the initial userns.
Ok, let me try to convert securityfs then.

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