linux-kernel - [RFC PATCH 03/30] ima: Bind ima namespace to the file descriptor

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Date:   Tue, 18 Aug 2020 17:20:10 +0200
From:   <krzysztof.struczynski@...wei.com>
To:     <linux-integrity@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <containers@...ts.linux-foundation.org>,
        <linux-security-module@...r.kernel.org>
CC:     Krzysztof Struczynski <krzysztof.struczynski@...wei.com>,
        <zohar@...ux.ibm.com>, <stefanb@...ux.vnet.ibm.com>,
        <sunyuqiong1988@...il.com>, <mkayaalp@...binghamton.edu>,
        <dmitry.kasatkin@...il.com>, <serge@...lyn.com>,
        <jmorris@...ei.org>, <christian@...uner.io>,
        <silviu.vlasceanu@...wei.com>, <roberto.sassu@...wei.com>
Subject: [RFC PATCH 03/30] ima: Bind ima namespace to the file descriptor

From: Krzysztof Struczynski <krzysztof.struczynski@...wei.com>

IMA namespace reference will be required in ima_file_free() to check
the policy and find inode integrity data for the correct ima namespace.
ima_file_free() is called on __fput(), and __fput() may be called after
releasing namespaces in exit_task_namespaces() in do_exit() and
therefore nsproxy reference cannot be used - it is already set to NULL.

This is a preparation for namespacing policy and inode integrity data.

Signed-off-by: Krzysztof Struczynski <krzysztof.struczynski@...wei.com>
---
 fs/file_table.c                   |  6 +++++-
 include/linux/fs.h                |  3 +++
 include/linux/ima.h               |  6 ++++++
 security/integrity/ima/ima_main.c | 27 +++++++++++++++++++++++++--
 4 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/fs/file_table.c b/fs/file_table.c
index 656647f9575a..878213d8af92 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -109,6 +109,8 @@ static struct file *__alloc_file(int flags, const struct cred *cred)
 		return ERR_PTR(error);
 	}
 
+	ima_file_alloc(f);
+
 	atomic_long_set(&f->f_count, 1);
 	rwlock_init(&f->f_owner.lock);
 	spin_lock_init(&f->f_lock);
@@ -259,8 +261,10 @@ static void __fput(struct file *file)
 	struct inode *inode = file->f_inode;
 	fmode_t mode = file->f_mode;
 
-	if (unlikely(!(file->f_mode & FMODE_OPENED)))
+	if (unlikely(!(file->f_mode & FMODE_OPENED))) {
+		ima_file_free(file);
 		goto out;
+	}
 
 	might_sleep();
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 407881ebeab1..8d6264755935 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -947,6 +947,9 @@ struct file {
 	struct address_space	*f_mapping;
 	errseq_t		f_wb_err;
 	errseq_t		f_sb_err; /* for syncfs */
+#ifdef CONFIG_IMA
+	void			*f_ima;
+#endif
 } __randomize_layout
   __attribute__((aligned(4)));	/* lest something weird decides that 2 is OK */
 
diff --git a/include/linux/ima.h b/include/linux/ima.h
index 5b6235b97603..3954cef57c00 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -21,6 +21,7 @@ struct llist_node;
 extern int ima_bprm_check(struct linux_binprm *bprm);
 extern int ima_file_check(struct file *file, int mask);
 extern void ima_post_create_tmpfile(struct inode *inode);
+extern int ima_file_alloc(struct file *file);
 extern void ima_file_free(struct file *file);
 extern int ima_file_mmap(struct file *file, unsigned long prot);
 extern int ima_file_mprotect(struct vm_area_struct *vma, unsigned long prot);
@@ -66,6 +67,11 @@ static inline void ima_post_create_tmpfile(struct inode *inode)
 {
 }
 
+static inline int ima_file_alloc(struct file *file)
+{
+	return 0;
+}
+
 static inline void ima_file_free(struct file *file)
 {
 	return;
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index d800e73c8b62..c7e29277b953 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -169,6 +169,23 @@ static void ima_check_last_writer(struct integrity_iint_cache *iint,
 	mutex_unlock(&iint->mutex);
 }
 
+/**
+ * ima_file_alloc - called on __alloc_file()
+ * @file: pointer to file structure being created
+ *
+ * Bind IMA namespace to the file descriptor. This is necessary, because
+ * __fput can be called after exit_task_namespaces() in do_exit().
+ * In that case nsproxy is already NULL and ima ns has to be found
+ * differently in ima_file_free(). If process joins different ima ns, files
+ * opened in the old ns will point to that (old) ns.
+ */
+int ima_file_alloc(struct file *file)
+{
+	file->f_ima = get_current_ns();
+	get_ima_ns((struct ima_namespace *)file->f_ima);
+	return 0;
+}
+
 /**
  * ima_file_free - called on __fput()
  * @file: pointer to file structure being freed
@@ -179,15 +196,21 @@ void ima_file_free(struct file *file)
 {
 	struct inode *inode = file_inode(file);
 	struct integrity_iint_cache *iint;
+	struct ima_namespace *ima_ns = (struct ima_namespace *)file->f_ima;
+
+	if (unlikely(!(file->f_mode & FMODE_OPENED)))
+		goto out;
 
 	if (!ima_policy_flag || !S_ISREG(inode->i_mode))
-		return;
+		goto out;
 
 	iint = integrity_iint_find(inode);
 	if (!iint)
-		return;
+		goto out;
 
 	ima_check_last_writer(iint, inode, file);
+out:
+	put_ima_ns(ima_ns);
 }
 
 static int process_measurement(struct file *file, const struct cred *cred,
-- 
2.20.1