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Subject[PATCH 6/6] Integrity: IMA file free imbalance
Date
The number of calls to ima_path_check()/ima_file_free()
should be balanced. An extra call to fput(), indicates
the file could have been accessed without first being
measured.

Although f_count is incremented/decremented in places other
than fget/fput, like fget_light/fput_light and get_file, the
current task must already hold a file refcnt. The call to
__fput() is delayed until the refcnt becomes 0, resulting
in ima_file_free() flagging any changes.

- add hook to increment opencount for IPC shared memory(SYSV)
and shmat files

Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
---
diff --git a/include/linux/ima.h b/include/linux/ima.h
index dcc3664..6db30a3 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -19,6 +19,7 @@ extern void ima_inode_free(struct inode *inode);
extern int ima_path_check(struct path *path, int mask);
extern void ima_file_free(struct file *file);
extern int ima_file_mmap(struct file *file, unsigned long prot);
+extern void ima_shm_check(struct file *file);

#else
static inline int ima_bprm_check(struct linux_binprm *bprm)
@@ -50,5 +51,10 @@ static inline int ima_file_mmap(struct file *file, unsigned long prot)
{
return 0;
}
+
+static inline void ima_shm_check(struct file *file)
+{
+ return;
+}
#endif /* CONFIG_IMA_H */
#endif /* _LINUX_IMA_H */
diff --git a/ipc/shm.c b/ipc/shm.c
index a9e09ad..5604bc8 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -39,6 +39,7 @@
#include <linux/nsproxy.h>
#include <linux/mount.h>
#include <linux/ipc_namespace.h>
+#include <linux/ima.h>

#include <asm/uaccess.h>

@@ -381,6 +382,7 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
error = PTR_ERR(file);
if (IS_ERR(file))
goto no_file;
+ ima_shm_check(file);

id = ipc_addid(&shm_ids(ns), &shp->shm_perm, ns->shm_ctlmni);
if (id < 0) {
@@ -881,6 +883,7 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
file = alloc_file(path.mnt, path.dentry, f_mode, &shm_file_operations);
if (!file)
goto out_free;
+ ima_shm_check(file);

file->private_data = sfd;
file->f_mapping = shp->shm_file->f_mapping;
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 5b72cdb..ed953fb 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -98,6 +98,7 @@ static inline unsigned long ima_hash_key(u8 *digest)

/* iint cache flags */
#define IMA_MEASURED 1
+#define IMA_IINT_DUMP_STACK 512

/* integrity data associated with an inode */
struct ima_iint_cache {
@@ -107,6 +108,7 @@ struct ima_iint_cache {
struct mutex mutex; /* protects: version, flags, digest */
long readcount; /* measured files readcount */
long writecount; /* measured files writecount */
+ long opencount; /* opens reference count */
struct kref refcount; /* ima_iint_cache reference count */
struct rcu_head rcu;
};
diff --git a/security/integrity/ima/ima_iint.c b/security/integrity/ima/ima_iint.c
index 750db3c..1f035e8 100644
--- a/security/integrity/ima/ima_iint.c
+++ b/security/integrity/ima/ima_iint.c
@@ -126,6 +126,7 @@ struct ima_iint_cache *ima_iint_find_insert_get(struct inode *inode)

return iint;
}
+EXPORT_SYMBOL_GPL(ima_iint_find_insert_get);

/* iint_free - called when the iint refcount goes to zero */
void iint_free(struct kref *kref)
@@ -134,6 +135,21 @@ void iint_free(struct kref *kref)
refcount);
iint->version = 0;
iint->flags = 0UL;
+ if (iint->readcount != 0) {
+ printk(KERN_INFO "%s: readcount: %ld\n", __FUNCTION__,
+ iint->readcount);
+ iint->readcount = 0;
+ }
+ if (iint->writecount != 0) {
+ printk(KERN_INFO "%s: writecount: %ld\n", __FUNCTION__,
+ iint->writecount);
+ iint->writecount = 0;
+ }
+ if (iint->opencount != 0) {
+ printk(KERN_INFO "%s: opencount: %ld\n", __FUNCTION__,
+ iint->opencount);
+ iint->opencount = 0;
+ }
kref_set(&iint->refcount, 1);
kmem_cache_free(iint_cache, iint);
}
@@ -174,6 +190,7 @@ static void init_once(void *foo)
mutex_init(&iint->mutex);
iint->readcount = 0;
iint->writecount = 0;
+ iint->opencount = 0;
kref_set(&iint->refcount, 1);
}

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 871e356..751a5d2 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -66,6 +66,19 @@ void ima_file_free(struct file *file)
return;

mutex_lock(&iint->mutex);
+ if (iint->opencount <= 0) {
+ printk(KERN_INFO
+ "%s: %s open/free imbalance (r:%ld w:%ld o:%ld f:%ld)\n",
+ __FUNCTION__, file->f_dentry->d_name.name,
+ iint->readcount, iint->writecount,
+ iint->opencount, atomic_long_read(&file->f_count));
+ if (!(iint->flags & IMA_IINT_DUMP_STACK)) {
+ dump_stack();
+ iint->flags |= IMA_IINT_DUMP_STACK;
+ }
+ }
+ iint->opencount--;
+
if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
iint->readcount--;

@@ -119,6 +132,7 @@ static int get_path_measurement(struct ima_iint_cache *iint, struct file *file,
pr_info("%s dentry_open failed\n", filename);
return rc;
}
+ iint->opencount++;
iint->readcount++;

rc = ima_collect_measurement(iint, file);
@@ -159,6 +173,7 @@ int ima_path_check(struct path *path, int mask)
return 0;

mutex_lock(&iint->mutex);
+ iint->opencount++;
if ((mask & MAY_WRITE) || (mask == 0))
iint->writecount++;
else if (mask & (MAY_READ | MAY_EXEC))
@@ -219,6 +234,20 @@ out:
return rc;
}

+static void opencount_get(struct file *file)
+{
+ struct inode *inode = file->f_dentry->d_inode;
+ struct ima_iint_cache *iint;
+
+ if (!ima_initialized || !S_ISREG(inode->i_mode))
+ return;
+ iint = ima_iint_find_insert_get(inode);
+ mutex_lock(&iint->mutex);
+ if (iint)
+ iint->opencount++;
+ mutex_unlock(&iint->mutex);
+}
+
/**
* ima_file_mmap - based on policy, collect/store measurement.
* @file: pointer to the file to be measured (May be NULL)
@@ -242,6 +271,18 @@ int ima_file_mmap(struct file *file, unsigned long prot)
return 0;
}

+/*
+ * ima_shm_check - IPC shm and shmat create/fput a file
+ *
+ * Maintain the opencount for these files to prevent unnecessary
+ * imbalance messages.
+ */
+void ima_shm_check(struct file *file)
+{
+ opencount_get(file);
+ return;
+}
+
/**
* ima_bprm_check - based on policy, collect/store measurement.
* @bprm: contains the linux_binprm structure
--
1.5.6.6


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