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Subject[PATCH] Smack: check permissions from user space
Date
Adds a new file into SmackFS called 'access'. Wanted
Smack permission is written into /smack/access.
After that result can be read from the opened file.
If access applies result contains 1 and otherwise
0. File access is protected from race conditions
by using simple_transaction_get()/set() API.

Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@intel.com>
---
security/smack/smack.h | 1 +
security/smack/smackfs.c | 181 ++++++++++++++++++++++++++++++----------------
2 files changed, 119 insertions(+), 63 deletions(-)
diff --git a/security/smack/smack.h b/security/smack/smack.h
index 2b6c6a5..82c5a30 100644
--- a/security/smack/smack.h
+++ b/security/smack/smack.h
@@ -189,6 +189,7 @@ struct smk_audit_info {
struct common_audit_data a;
#endif
};
+
/*
* These functions are in smack_lsm.c
*/
diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index f934601..5a87075 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -27,6 +27,7 @@
#include <linux/seq_file.h>
#include <linux/ctype.h>
#include <linux/audit.h>
+#include <linux/smack.h>
#include "smack.h"

/*
@@ -44,6 +45,7 @@ enum smk_inos {
SMK_ONLYCAP = 9, /* the only "capable" label */
SMK_LOGGING = 10, /* logging */
SMK_LOAD_SELF = 11, /* task specific rules */
+ SMK_ACCESSES = 12, /* access policy */
};

/*
@@ -176,71 +178,19 @@ static int smk_set_access(struct smack_rule *srp, struct list_head *rule_list,
}

/**
- * smk_write_load_list - write() for any /smack/load
- * @file: file pointer, not actually used
- * @buf: where to get the data from
- * @count: bytes sent
- * @ppos: where to start - must be 0
- * @rule_list: the list of rules to write to
- * @rule_lock: lock for the rule list
- *
- * Get one smack access rule from above.
- * The format is exactly:
- * char subject[SMK_LABELLEN]
- * char object[SMK_LABELLEN]
- * char access[SMK_ACCESSLEN]
- *
- * writes must be SMK_LABELLEN+SMK_LABELLEN+SMK_ACCESSLEN bytes.
+ * smk_parse_rule - parse subject, object and access type
+ * @data: string to be parsed whose size is SMK_LOADLEN
+ * @rule: parsed entities are stored in here
*/
-static ssize_t smk_write_load_list(struct file *file, const char __user *buf,
- size_t count, loff_t *ppos,
- struct list_head *rule_list,
- struct mutex *rule_lock)
+static int smk_parse_rule(const char *data, struct smack_rule *rule)
{
- struct smack_rule *rule;
- char *data;
- int rc = -EINVAL;
-
- /*
- * No partial writes.
- * Enough data must be present.
- */
- if (*ppos != 0)
- return -EINVAL;
- /*
- * Minor hack for backward compatibility
- */
- if (count < (SMK_OLOADLEN) || count > SMK_LOADLEN)
- return -EINVAL;
-
- data = kzalloc(SMK_LOADLEN, GFP_KERNEL);
- if (data == NULL)
- return -ENOMEM;
-
- if (copy_from_user(data, buf, count) != 0) {
- rc = -EFAULT;
- goto out;
- }
-
- /*
- * More on the minor hack for backward compatibility
- */
- if (count == (SMK_OLOADLEN))
- data[SMK_OLOADLEN] = '-';
-
- rule = kzalloc(sizeof(*rule), GFP_KERNEL);
- if (rule == NULL) {
- rc = -ENOMEM;
- goto out;
- }
-
rule->smk_subject = smk_import(data, 0);
if (rule->smk_subject == NULL)
- goto out_free_rule;
+ return -1;

rule->smk_object = smk_import(data + SMK_LABELLEN, 0);
if (rule->smk_object == NULL)
- goto out_free_rule;
+ return -1;

rule->smk_access = 0;

@@ -252,7 +202,7 @@ static ssize_t smk_write_load_list(struct file *file, const char __user *buf,
rule->smk_access |= MAY_READ;
break;
default:
- goto out_free_rule;
+ return -1;
}

switch (data[SMK_LABELLEN + SMK_LABELLEN + 1]) {
@@ -263,7 +213,7 @@ static ssize_t smk_write_load_list(struct file *file, const char __user *buf,
rule->smk_access |= MAY_WRITE;
break;
default:
- goto out_free_rule;
+ return -1;
}

switch (data[SMK_LABELLEN + SMK_LABELLEN + 2]) {
@@ -274,7 +224,7 @@ static ssize_t smk_write_load_list(struct file *file, const char __user *buf,
rule->smk_access |= MAY_EXEC;
break;
default:
- goto out_free_rule;
+ return -1;
}

switch (data[SMK_LABELLEN + SMK_LABELLEN + 3]) {
@@ -285,7 +235,7 @@ static ssize_t smk_write_load_list(struct file *file, const char __user *buf,
rule->smk_access |= MAY_APPEND;
break;
default:
- goto out_free_rule;
+ return -1;
}

switch (data[SMK_LABELLEN + SMK_LABELLEN + 4]) {
@@ -296,9 +246,74 @@ static ssize_t smk_write_load_list(struct file *file, const char __user *buf,
rule->smk_access |= MAY_TRANSMUTE;
break;
default:
- goto out_free_rule;
+ return -1;
}

+ return 0;
+}
+
+/**
+ * smk_write_load_list - write() for any /smack/load
+ * @file: file pointer, not actually used
+ * @buf: where to get the data from
+ * @count: bytes sent
+ * @ppos: where to start - must be 0
+ * @rule_list: the list of rules to write to
+ * @rule_lock: lock for the rule list
+ *
+ * Get one smack access rule from above.
+ * The format is exactly:
+ * char subject[SMK_LABELLEN]
+ * char object[SMK_LABELLEN]
+ * char access[SMK_ACCESSLEN]
+ *
+ * writes must be SMK_LABELLEN+SMK_LABELLEN+SMK_ACCESSLEN bytes.
+ */
+static ssize_t smk_write_load_list(struct file *file, const char __user *buf,
+ size_t count, loff_t *ppos,
+ struct list_head *rule_list,
+ struct mutex *rule_lock)
+{
+ struct smack_rule *rule;
+ char *data;
+ int rc = -EINVAL;
+
+ /*
+ * No partial writes.
+ * Enough data must be present.
+ */
+ if (*ppos != 0)
+ return -EINVAL;
+ /*
+ * Minor hack for backward compatibility
+ */
+ if (count < (SMK_OLOADLEN) || count > SMK_LOADLEN)
+ return -EINVAL;
+
+ data = kzalloc(SMK_LOADLEN, GFP_KERNEL);
+ if (data == NULL)
+ return -ENOMEM;
+
+ if (copy_from_user(data, buf, count) != 0) {
+ rc = -EFAULT;
+ goto out;
+ }
+
+ /*
+ * More on the minor hack for backward compatibility
+ */
+ if (count == (SMK_OLOADLEN))
+ data[SMK_OLOADLEN] = '-';
+
+ rule = kzalloc(sizeof(*rule), GFP_KERNEL);
+ if (rule == NULL) {
+ rc = -ENOMEM;
+ goto out;
+ }
+
+ if (smk_parse_rule(data, rule))
+ goto out_free_rule;
+
rc = count;
/*
* smk_set_access returns true if there was already a rule
@@ -1425,6 +1440,44 @@ static const struct file_operations smk_load_self_ops = {
.write = smk_write_load_self,
.release = seq_release,
};
+
+/**
+ * smk_write_access - handle access check transaction
+ * @file: file pointer
+ * @buf: data from user space
+ * @count: bytes sent
+ * @ppos: where to start - must be 0
+ */
+static ssize_t smk_write_access(struct file *file, const char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ struct smack_rule rule;
+ char *data;
+
+ if (!capable(CAP_MAC_ADMIN))
+ return -EPERM;
+
+ data = simple_transaction_get(file, buf, count);
+ if (IS_ERR(data))
+ return PTR_ERR(data);
+
+ if (count < SMK_LOADLEN || smk_parse_rule(data, &rule))
+ return -EINVAL;
+
+ data[0] = smk_access(rule.smk_subject, rule.smk_object,
+ rule.smk_access, NULL) == 0;
+
+ simple_transaction_set(file, 1);
+ return SMK_LOADLEN;
+}
+
+static const struct file_operations smk_access_ops = {
+ .write = smk_write_access,
+ .read = simple_transaction_read,
+ .release = simple_transaction_release,
+ .llseek = generic_file_llseek,
+};
+
/**
* smk_fill_super - fill the /smackfs superblock
* @sb: the empty superblock
@@ -1459,6 +1512,8 @@ static int smk_fill_super(struct super_block *sb, void *data, int silent)
"logging", &smk_logging_ops, S_IRUGO|S_IWUSR},
[SMK_LOAD_SELF] = {
"load-self", &smk_load_self_ops, S_IRUGO|S_IWUGO},
+ [SMK_ACCESSES] = {
+ "access", &smk_access_ops, S_IRUGO|S_IWUSR},
/* last one */
{""}
};
--
1.7.4.1


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