Re: [PATCH v5 15/16] ima: Move dentries into ima_namespace
From: Stefan Berger
Date: Thu Dec 09 2021 - 10:01:27 EST
On 12/9/21 09:41, Christian Brauner wrote:
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@xxxxxxxxxxxxx>
---
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.
I thought that securityfs_remove() will now simply influence when a
dentry is removed and freed. If we call it in the error cleanup path in
non-init_user_ns case it would go away right there and leave nothing to
do for .kill_sb() while an additional dget() would require the cleanup
as well but do another cleanup then in .kill_sb() since that brings the
reference count to 0 via the dput()s that it does. Am I wrong on this?
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.
I moved the dentries into the ima_namespace so that each namespace holds
a pointer to the dentries it owns and isolates them. We certainly
wouldn't want to have IMA namespaces write over the current static
variables and create a mess with what these are pointing to (
https://elixir.bootlin.com/linux/latest/source/security/integrity/ima/ima_fs.c#L359
) and possible race conditions when doing parallel initialization (if
that's possible at all). This also reduces the code size and we don't
need two different implementations for init_user_ns and
non-init_user_ns. So I don't quite understand whey we wouldn't want to
have the dentries isolated via ima_namespace?
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