Re: [PATCH v5 13/16] ima: Move some IMA policy and filesystem related variables into ima_namespace

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On 12/9/21 14:11, Christian Brauner wrote:
On Wed, Dec 08, 2021 at 05:18:15PM -0500, Stefan Berger wrote:
Move the ima_write_mutex, ima_fs_flag, and valid_policy variables into
ima_namespace. This way each IMA namespace can set those variables
independently.

Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
---
  include/linux/ima.h                      |  5 ++++
  security/integrity/ima/ima_fs.c          | 32 +++++++++++-------------
  security/integrity/ima/ima_init_ima_ns.c |  4 +++
  3 files changed, 23 insertions(+), 18 deletions(-)

diff --git a/include/linux/ima.h b/include/linux/ima.h
index 2ce801bfc449..3aaf6e806db4 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -261,6 +261,11 @@ struct ima_namespace {
  	struct ima_h_table ima_htable;
  	struct list_head ima_measurements;
  	unsigned long binary_runtime_size;
+
+	/* IMA's filesystem */
+	struct mutex ima_write_mutex;
+	unsigned long ima_fs_flags;
+	int valid_policy;
  };
extern struct ima_namespace init_ima_ns;
diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index 38b1c26479b3..0e582ceecc7f 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -25,8 +25,6 @@
#include "ima.h" -static DEFINE_MUTEX(ima_write_mutex);
-
  bool ima_canonical_fmt;
  static int __init default_canonical_fmt_setup(char *str)
  {
@@ -37,8 +35,6 @@ static int __init default_canonical_fmt_setup(char *str)
  }
  __setup("ima_canonical_fmt", default_canonical_fmt_setup);
-static int valid_policy = 1;
-
  static ssize_t ima_show_htable_value(char __user *buf, size_t count,
  				     loff_t *ppos, atomic_long_t *val)
  {
@@ -339,7 +335,7 @@ static ssize_t ima_write_policy(struct file *file, const char __user *buf,
  		goto out;
  	}
- result = mutex_lock_interruptible(&ima_write_mutex);
+	result = mutex_lock_interruptible(&ns->ima_write_mutex);
  	if (result < 0)
  		goto out_free;
@@ -354,12 +350,12 @@ static ssize_t ima_write_policy(struct file *file, const char __user *buf,
  	} else {
  		result = ima_parse_add_rule(ns, data);
  	}
-	mutex_unlock(&ima_write_mutex);
+	mutex_unlock(&ns->ima_write_mutex);
  out_free:
  	kfree(data);
  out:
  	if (result < 0)
-		valid_policy = 0;
+		ns->valid_policy = 0;
return result;
  }
@@ -376,8 +372,6 @@ enum ima_fs_flags {
  	IMA_FS_BUSY,
  };
-static unsigned long ima_fs_flags;
-
  #ifdef	CONFIG_IMA_READ_POLICY
  static const struct seq_operations ima_policy_seqops = {
  		.start = ima_policy_start,
@@ -392,6 +386,8 @@ static const struct seq_operations ima_policy_seqops = {
   */
  static int ima_open_policy(struct inode *inode, struct file *filp)
  {
+	struct ima_namespace *ns = get_current_ns();
+
I'm a bit confused here. In all those callbacks:
	.open = ima_open_policy,
	.write = ima_write_policy,
	.release = ima_release_policy,
you're calling get_current_ns() at the top of it. What guarantees that
the same ima_namespace is returned here? What if the fd is sent to
someone who is in a different user namespace and the write to that
file?

Maybe I'm just confused but wouldn't you want something like this?

I hadn't thought about inheritance or passing fds. But yes. I will adopt your patch and extend all the files to tie them to the user namespace they are opened in...

Thanks.



 From 1f03dc427c583d5e9ebc9ebe9de77c3c535bbebe Mon Sep 17 00:00:00 2001
From: Christian Brauner <christian.brauner@xxxxxxxxxx>
Date: Thu, 9 Dec 2021 20:07:02 +0100
Subject: [PATCH] !!!! HERE BE DRAGONS - UNTESTED !!!!

---
  security/integrity/ima/ima_fs.c | 43 +++++++++++++++++++++++++++++----
  1 file changed, 38 insertions(+), 5 deletions(-)

diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index 583462b29cb5..d5b302b925b8 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -317,10 +317,14 @@ static ssize_t ima_read_policy(char *path)
  static ssize_t ima_write_policy(struct file *file, const char __user *buf,
  				size_t datalen, loff_t *ppos)
  {
-	struct ima_namespace *ns = get_current_ns();
+	struct ima_namespace *ns;
+	struct user_namespace *user_ns;
  	char *data;
  	ssize_t result;
+ user_ns = ima_filp_private(filp);
+	ns = user_ns->ima_ns
+
  	if (datalen >= PAGE_SIZE)
  		datalen = PAGE_SIZE - 1;
@@ -373,26 +377,51 @@ static const struct seq_operations ima_policy_seqops = {
  };
  #endif
+static struct user_namespace *ima_filp_private(struct file *filp)
+{
+	if (!(filp->f_flags & O_WRONLY)) {
+#ifdef CONFIG_IMA_READ_POLICY
+		struct seq_file *seq;
+
+		seq = filp->private_data;
+		return seq->private;
+#endif
+	}
+	return filp->private_data;
+}
+
  /*
   * ima_open_policy: sequentialize access to the policy file
   */
  static int ima_open_policy(struct inode *inode, struct file *filp)
  {
-	struct ima_namespace *ns = get_current_ns();
+	struct user_namespace *user_ns = current_user_ns();
+	struct ima_namespace *ns = user_ns->ima_ns;
if (!(filp->f_flags & O_WRONLY)) {
  #ifndef	CONFIG_IMA_READ_POLICY
  		return -EACCES;
  #else
+		int err;
+		struct seq_file *seq;
+
  		if ((filp->f_flags & O_ACCMODE) != O_RDONLY)
  			return -EACCES;
-		if (!mac_admin_ns_capable(ima_user_ns(ns)))
+		if (!mac_admin_ns_capable(user_ns))
  			return -EPERM;
-		return seq_open(filp, &ima_policy_seqops);
+		err = seq_open(filp, &ima_policy_seqops);
+		if (err)
+			return err;
+
+		seq = filp->private_data;
+		seq->private = user_ns;
+		return 0;
  #endif
  	}
  	if (test_and_set_bit(IMA_FS_BUSY, &ns->ima_fs_flags))
  		return -EBUSY;
+
+	filp->private_data = user_ns;
  	return 0;
  }
@@ -405,9 +434,13 @@ static int ima_open_policy(struct inode *inode, struct file *filp)
   */
  static int ima_release_policy(struct inode *inode, struct file *file)
  {
-	struct ima_namespace *ns = get_current_ns();
+	struct ima_namespace *ns;
+	struct user_namespace *user_ns;
  	const char *cause = ns->valid_policy ? "completed" : "failed";
+ user_ns = ima_filp_private(filp);
+	ns = user_ns->ima_ns
+
  	if ((file->f_flags & O_ACCMODE) == O_RDONLY)
  		return seq_release(inode, file);



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