Re: [PATCH v5 15/16] ima: Move dentries into ima_namespace

[Christian Brauner <christian.brauner@ubuntu.com>]

On Thu, Dec 09, 2021 at 03:37:49PM +0100, Christian Brauner wrote:
> On Thu, Dec 09, 2021 at 03:34:28PM +0100, Christian Brauner wrote:
> > On Wed, Dec 08, 2021 at 05:18:17PM -0500, Stefan Berger wrote:
> > > Move the dentries into the ima_namespace for reuse by virtualized
> > > SecurityFS. Implement function freeing the dentries in order of
> > > files and symlinks before directories.
> > > 
> > > Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
> > > ---
> > 
> > This doesn't work as implemented, I think.
> > 
> > What I would have preferred and what I tried to explain in the earlier
> > review was:
> > Keep the dentry stashing global since it is only needed for init_ima_ns.
> > Then struct ima_namespace becomes way smaller and simpler.
> > If you do that then it makes sense to remove the additional dget() in
> > securityfs_create_dentry() for non-init_ima_ns.
> > Then you can rely on auto-cleanup in .kill_sb() or on
> > ima_securityfs_init() failure and you only need to call
> > ima_fs_ns_free_dentries() if ns != init_ima_ns.

s/ns != init_ima_ns/ns == init_ima_ns/

> > 
> > IIuc, it seems you're currently doing one dput() too many since you're
> > calling securityfs_remove() in the error path for non-init_ima_ns which
> > relies on the previous increased dget() which we removed.
> 
> If you really want to move the dentry stashing into struct ima_namespace
> even though it's really unnecessary then you may as well not care about
> the auto-cleanup and keep that additional ima_fs_ns_free_dentries(ns)
> call in .kill_sb(). But I really think not dragging dentry stashing into
> struct ima_namespace is the correct way to go about this.
> 
> > 
> > >  include/linux/ima.h             | 13 ++++++
> > >  security/integrity/ima/ima_fs.c | 72 ++++++++++++++++++---------------
> > >  2 files changed, 52 insertions(+), 33 deletions(-)
> > > 
> > > diff --git a/include/linux/ima.h b/include/linux/ima.h
> > > index 3aaf6e806db4..4dd64e318b15 100644
> > > --- a/include/linux/ima.h
> > > +++ b/include/linux/ima.h
> > > @@ -220,6 +220,17 @@ struct ima_h_table {
> > >  	struct hlist_head queue[IMA_MEASURE_HTABLE_SIZE];
> > >  };
> > >  
> > > +enum {
> > > +	IMAFS_DENTRY_DIR = 0,
> > > +	IMAFS_DENTRY_SYMLINK,
> > > +	IMAFS_DENTRY_BINARY_RUNTIME_MEASUREMENTS,
> > > +	IMAFS_DENTRY_ASCII_RUNTIME_MEASUREMENTS,
> > > +	IMAFS_DENTRY_RUNTIME_MEASUREMENTS_COUNT,
> > > +	IMAFS_DENTRY_VIOLATIONS,
> > > +	IMAFS_DENTRY_IMA_POLICY,
> > > +	IMAFS_DENTRY_LAST
> > > +};
> > > +
> > >  struct ima_namespace {
> > >  	struct kref kref;
> > >  	struct user_namespace *user_ns;
> > > @@ -266,6 +277,8 @@ struct ima_namespace {
> > >  	struct mutex ima_write_mutex;
> > >  	unsigned long ima_fs_flags;
> > >  	int valid_policy;
> > > +
> > > +	struct dentry *dentry[IMAFS_DENTRY_LAST];
> > >  };
> > >  
> > >  extern struct ima_namespace init_ima_ns;
> > > diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
> > > index a749a3e79304..3810d11fb463 100644
> > > --- a/security/integrity/ima/ima_fs.c
> > > +++ b/security/integrity/ima/ima_fs.c
> > > @@ -360,14 +360,6 @@ static ssize_t ima_write_policy(struct file *file, const char __user *buf,
> > >  	return result;
> > >  }
> > >  
> > > -static struct dentry *ima_dir;
> > > -static struct dentry *ima_symlink;
> > > -static struct dentry *binary_runtime_measurements;
> > > -static struct dentry *ascii_runtime_measurements;
> > > -static struct dentry *runtime_measurements_count;
> > > -static struct dentry *violations;
> > > -static struct dentry *ima_policy;
> > > -
> > >  enum ima_fs_flags {
> > >  	IMA_FS_BUSY,
> > >  };
> > > @@ -437,8 +429,8 @@ static int ima_release_policy(struct inode *inode, struct file *file)
> > >  
> > >  	ima_update_policy(ns);
> > >  #if !defined(CONFIG_IMA_WRITE_POLICY) && !defined(CONFIG_IMA_READ_POLICY)
> > > -	securityfs_remove(ima_policy);
> > > -	ima_policy = NULL;
> > > +	securityfs_remove(ns->dentry[IMAFS_DENTRY_IMA_POLICY]);
> > > +	ns->dentry[IMAFS_DENTRY_IMA_POLICY] = NULL;
> > >  #elif defined(CONFIG_IMA_WRITE_POLICY)
> > >  	clear_bit(IMA_FS_BUSY, &ns->ima_fs_flags);
> > >  #elif defined(CONFIG_IMA_READ_POLICY)
> > > @@ -455,58 +447,72 @@ static const struct file_operations ima_measure_policy_ops = {
> > >  	.llseek = generic_file_llseek,
> > >  };
> > >  
> > > -int __init ima_fs_init(void)
> > > +static void ima_fs_ns_free_dentries(struct ima_namespace *ns)
> > >  {
> > > -	ima_dir = securityfs_create_dir("ima", integrity_dir);
> > > -	if (IS_ERR(ima_dir))
> > > +	int i;
> > > +
> > > +	for (i = IMAFS_DENTRY_LAST - 1; i >= 0; i--)
> > > +		securityfs_remove(ns->dentry[i]);
> > > +
> > > +	memset(ns->dentry, 0, sizeof(ns->dentry));
> > > +}
> > > +
> > > +static int __init ima_securityfs_init(struct user_namespace *user_ns)
> > > +{
> > > +	struct ima_namespace *ns = user_ns->ima_ns;
> > > +	struct dentry *ima_dir;
> > > +
> > > +	ns->dentry[IMAFS_DENTRY_DIR] = securityfs_create_dir("ima", integrity_dir);
> > > +	if (IS_ERR(ns->dentry[IMAFS_DENTRY_DIR]))
> > >  		return -1;
> > > +	ima_dir = ns->dentry[IMAFS_DENTRY_DIR];
> > >  
> > > -	ima_symlink = securityfs_create_symlink("ima", NULL, "integrity/ima",
> > > -						NULL);
> > > -	if (IS_ERR(ima_symlink))
> > > +	ns->dentry[IMAFS_DENTRY_SYMLINK] =
> > > +	    securityfs_create_symlink("ima", NULL, "integrity/ima", NULL);
> > > +	if (IS_ERR(ns->dentry[IMAFS_DENTRY_SYMLINK]))
> > >  		goto out;
> > >  
> > > -	binary_runtime_measurements =
> > > +	ns->dentry[IMAFS_DENTRY_BINARY_RUNTIME_MEASUREMENTS] =
> > >  	    securityfs_create_file("binary_runtime_measurements",
> > >  				   S_IRUSR | S_IRGRP, ima_dir, NULL,
> > >  				   &ima_measurements_ops);
> > > -	if (IS_ERR(binary_runtime_measurements))
> > > +	if (IS_ERR(ns->dentry[IMAFS_DENTRY_BINARY_RUNTIME_MEASUREMENTS]))
> > >  		goto out;
> > >  
> > > -	ascii_runtime_measurements =
> > > +	ns->dentry[IMAFS_DENTRY_ASCII_RUNTIME_MEASUREMENTS] =
> > >  	    securityfs_create_file("ascii_runtime_measurements",
> > >  				   S_IRUSR | S_IRGRP, ima_dir, NULL,
> > >  				   &ima_ascii_measurements_ops);
> > > -	if (IS_ERR(ascii_runtime_measurements))
> > > +	if (IS_ERR(ns->dentry[IMAFS_DENTRY_ASCII_RUNTIME_MEASUREMENTS]))
> > >  		goto out;
> > >  
> > > -	runtime_measurements_count =
> > > +	ns->dentry[IMAFS_DENTRY_RUNTIME_MEASUREMENTS_COUNT] =
> > >  	    securityfs_create_file("runtime_measurements_count",
> > >  				   S_IRUSR | S_IRGRP, ima_dir, NULL,
> > >  				   &ima_measurements_count_ops);
> > > -	if (IS_ERR(runtime_measurements_count))
> > > +	if (IS_ERR(ns->dentry[IMAFS_DENTRY_RUNTIME_MEASUREMENTS_COUNT]))
> > >  		goto out;
> > >  
> > > -	violations =
> > > +	ns->dentry[IMAFS_DENTRY_VIOLATIONS] =
> > >  	    securityfs_create_file("violations", S_IRUSR | S_IRGRP,
> > >  				   ima_dir, NULL, &ima_htable_violations_ops);
> > > -	if (IS_ERR(violations))
> > > +	if (IS_ERR(ns->dentry[IMAFS_DENTRY_VIOLATIONS]))
> > >  		goto out;
> > >  
> > > -	ima_policy = securityfs_create_file("policy", POLICY_FILE_FLAGS,
> > > +	ns->dentry[IMAFS_DENTRY_IMA_POLICY] =
> > > +	    securityfs_create_file("policy", POLICY_FILE_FLAGS,
> > >  					    ima_dir, NULL,
> > >  					    &ima_measure_policy_ops);
> > > -	if (IS_ERR(ima_policy))
> > > +	if (IS_ERR(ns->dentry[IMAFS_DENTRY_IMA_POLICY]))
> > >  		goto out;
> > >  
> > >  	return 0;
> > >  out:
> > > -	securityfs_remove(violations);
> > > -	securityfs_remove(runtime_measurements_count);
> > > -	securityfs_remove(ascii_runtime_measurements);
> > > -	securityfs_remove(binary_runtime_measurements);
> > > -	securityfs_remove(ima_symlink);
> > > -	securityfs_remove(ima_dir);
> > > -	securityfs_remove(ima_policy);
> > > +	ima_fs_ns_free_dentries(ns);
> > >  	return -1;
> > >  }
> > > +
> > > +int __init ima_fs_init(void)
> > > +{
> > > +	return ima_securityfs_init(&init_user_ns);
> > > +}
> > > -- 
> > > 2.31.1
> > > 
> > > 
> > 
>