[PATCH 2/2] Smack: allow multiple labels in onlycap

From: Rafal Krypa
Date: Thu May 21 2015 - 12:25:17 EST

Smack onlycap allows limiting of CAP_MAC_ADMIN and CAP_MAC_OVERRIDE to
processes running with the configured label. But having single privileged
label is not enough in some real use cases. On a complex system like Tizen,
there maybe few programs that need to configure Smack policy in run-time
and running them all with a single label is not always practical.
This patch extends onlycap feature for multiple labels. They are configured
in the same smackfs "onlycap" interface, separated by spaces.

Signed-off-by: Rafal Krypa <r.krypa@xxxxxxxxxxx>
---
Documentation/security/Smack.txt | 6 +-
security/smack/smack.h | 25 +++---
security/smack/smack_access.c | 41 ++++++++++
security/smack/smackfs.c | 162 ++++++++++++++++++++++++++-------------
4 files changed, 162 insertions(+), 72 deletions(-)

diff --git a/Documentation/security/Smack.txt b/Documentation/security/Smack.txt
index abc82f8..de5e1ae 100644
--- a/Documentation/security/Smack.txt
+++ b/Documentation/security/Smack.txt
@@ -206,11 +206,11 @@ netlabel
label. The format accepted on write is:
"%d.%d.%d.%d label" or "%d.%d.%d.%d/%d label".
onlycap
- This contains the label processes must have for CAP_MAC_ADMIN
+ This contains labels processes must have for CAP_MAC_ADMIN
and CAP_MAC_OVERRIDE to be effective. If this file is empty
these capabilities are effective at for processes with any
- label. The value is set by writing the desired label to the
- file or cleared by writing "-" to the file.
+ label. The values are set by writing the desired labels, separated
+ by spaces, to the file or cleared by writing "-" to the file.
ptrace
This is used to define the current ptrace policy
0 - default: this is the policy that relies on Smack access rules.
diff --git a/security/smack/smack.h b/security/smack/smack.h
index b8c1a86..244e035 100644
--- a/security/smack/smack.h
+++ b/security/smack/smack.h
@@ -138,6 +138,11 @@ struct smk_port_label {
struct smack_known *smk_out; /* outgoing label */
};

+struct smack_onlycap {
+ struct list_head list;
+ struct smack_known *smk_label;
+};
+
/*
* Mount options
*/
@@ -249,6 +254,7 @@ int smk_netlbl_mls(int, char *, struct netlbl_lsm_secattr *, int);
struct smack_known *smk_import_entry(const char *, int);
void smk_insert_entry(struct smack_known *skp);
struct smack_known *smk_find_entry(const char *);
+int smack_privileged(int cap);

/*
* Shared data.
@@ -257,7 +263,6 @@ extern int smack_enabled;
extern int smack_cipso_direct;
extern int smack_cipso_mapped;
extern struct smack_known *smack_net_ambient;
-extern struct smack_known *smack_onlycap;
extern struct smack_known *smack_syslog_label;
#ifdef CONFIG_SECURITY_SMACK_BRINGUP
extern struct smack_known *smack_unconfined;
@@ -276,6 +281,9 @@ extern struct mutex smack_known_lock;
extern struct list_head smack_known_list;
extern struct list_head smk_netlbladdr_list;

+extern struct mutex smack_onlycap_lock;
+extern struct list_head smack_onlycap_list;
+
#define SMACK_HASH_SLOTS 16
extern struct hlist_head smack_known_hash[SMACK_HASH_SLOTS];

@@ -332,21 +340,6 @@ static inline struct smack_known *smk_of_current(void)
}

/*
- * Is the task privileged and allowed to be privileged
- * by the onlycap rule.
- */
-static inline int smack_privileged(int cap)
-{
- struct smack_known *skp = smk_of_current();
-
- if (!capable(cap))
- return 0;
- if (smack_onlycap == NULL || smack_onlycap == skp)
- return 1;
- return 0;
-}
-
-/*
* logging functions
*/
#define SMACK_AUDIT_DENIED 0x1
diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
index 408e20b..00f6b38 100644
--- a/security/smack/smack_access.c
+++ b/security/smack/smack_access.c
@@ -617,3 +617,44 @@ struct smack_known *smack_from_secid(const u32 secid)
rcu_read_unlock();
return &smack_known_invalid;
}
+
+/*
+ * Unless a process is running with one of these labels
+ * even having CAP_MAC_OVERRIDE isn't enough to grant
+ * privilege to violate MAC policy. If no labels are
+ * designated (the empty list case) capabilities apply to
+ * everyone.
+ */
+LIST_HEAD(smack_onlycap_list);
+DEFINE_MUTEX(smack_onlycap_lock);
+
+/*
+ * Is the task privileged and allowed to be privileged
+ * by the onlycap rule.
+ *
+ * Returns 1 if the task is allowed to be privileged, 0 if it's not.
+ */
+int smack_privileged(int cap)
+{
+ struct smack_known *skp = smk_of_current();
+ struct smack_onlycap *sop;
+
+ if (!capable(cap))
+ return 0;
+
+ rcu_read_lock();
+ if (list_empty(&smack_onlycap_list)) {
+ rcu_read_unlock();
+ return 1;
+ }
+
+ list_for_each_entry_rcu(sop, &smack_onlycap_list, list) {
+ if (sop->smk_label == skp) {
+ rcu_read_unlock();
+ return 1;
+ }
+ }
+ rcu_read_unlock();
+
+ return 0;
+}
diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
index e40dc48..2aabcb2 100644
--- a/security/smack/smackfs.c
+++ b/security/smack/smackfs.c
@@ -87,16 +87,6 @@ int smack_cipso_direct = SMACK_CIPSO_DIRECT_DEFAULT;
*/
int smack_cipso_mapped = SMACK_CIPSO_MAPPED_DEFAULT;

-/*
- * Unless a process is running with this label even
- * having CAP_MAC_OVERRIDE isn't enough to grant
- * privilege to violate MAC policy. If no label is
- * designated (the NULL case) capabilities apply to
- * everyone. It is expected that the hat (^) label
- * will be used if any label is used.
- */
-struct smack_known *smack_onlycap;
-
#ifdef CONFIG_SECURITY_SMACK_BRINGUP
/*
* Allow one label to be unconfined. This is for
@@ -1636,34 +1626,78 @@ static const struct file_operations smk_ambient_ops = {
.llseek = default_llseek,
};

-/**
- * smk_read_onlycap - read() for smackfs/onlycap
- * @filp: file pointer, not actually used
- * @buf: where to put the result
- * @cn: maximum to send along
- * @ppos: where to start
- *
- * Returns number of bytes read or error code, as appropriate
+/*
+ * Seq_file operations for /smack/onlycap
*/
-static ssize_t smk_read_onlycap(struct file *filp, char __user *buf,
- size_t cn, loff_t *ppos)
+static void *onlycap_seq_start(struct seq_file *s, loff_t *pos)
{
- char *smack = "";
- ssize_t rc = -EINVAL;
- int asize;
+ return smk_seq_start(s, pos, &smack_onlycap_list);
+}

- if (*ppos != 0)
- return 0;
+static void *onlycap_seq_next(struct seq_file *s, void *v, loff_t *pos)
+{
+ return smk_seq_next(s, v, pos, &smack_onlycap_list);
+}

- if (smack_onlycap != NULL)
- smack = smack_onlycap->smk_known;
+static int onlycap_seq_show(struct seq_file *s, void *v)
+{
+ struct list_head *list = v;
+ struct smack_onlycap *sop =
+ list_entry_rcu(list, struct smack_onlycap, list);

- asize = strlen(smack) + 1;
+ seq_puts(s, sop->smk_label->smk_known);
+ seq_putc(s, ' ');

- if (cn >= asize)
- rc = simple_read_from_buffer(buf, cn, ppos, smack, asize);
+ return 0;
+}

- return rc;
+static const struct seq_operations onlycap_seq_ops = {
+ .start = onlycap_seq_start,
+ .next = onlycap_seq_next,
+ .show = onlycap_seq_show,
+ .stop = smk_seq_stop,
+};
+
+static int smk_open_onlycap(struct inode *inode, struct file *file)
+{
+ return seq_open(file, &onlycap_seq_ops);
+}
+
+/**
+ * list_swap_rcu - swap public list with a private one in RCU-safe way
+ * The caller must hold appropriate mutex to prevent concurrent modifications
+ * to the public list.
+ * Private list is assumed to be not accessible to other threads yet.
+ *
+ * @public: public list
+ * @private: private list
+ */
+static void list_swap_rcu(struct list_head *public, struct list_head *private)
+{
+ struct list_head *first, *last;
+
+ if (list_empty(public)) {
+ list_splice_init_rcu(private, public, synchronize_rcu);
+ } else {
+ /* Remember public list before replacing it */
+ first = public->next;
+ last = public->prev;
+
+ /* Publish private list in place of public in RCU-safe way */
+ private->prev->next = public;
+ private->next->prev = public;
+ rcu_assign_pointer(public->next, private->next);
+ public->prev = private->prev;
+
+ synchronize_rcu();
+
+ /* When all readers are done with the old public list,
+ * attach it in place of private */
+ private->next = first;
+ private->prev = last;
+ first->prev = private;
+ last->next = private;
+ }
}

/**
@@ -1679,28 +1713,47 @@ static ssize_t smk_write_onlycap(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
char *data;
- struct smack_known *skp = smk_of_task(current->cred->security);
+ char *data_parse
+ char *tok;
+ struct smack_known *skp;
+ struct smack_onlycap *sop;
+ struct smack_onlycap *sop2;
+ LIST_HEAD(list_tmp);
int rc = count;

if (!smack_privileged(CAP_MAC_ADMIN))
return -EPERM;

- /*
- * This can be done using smk_access() but is done
- * explicitly for clarity. The smk_access() implementation
- * would use smk_access(smack_onlycap, MAY_WRITE)
- */
- if (smack_onlycap != NULL && smack_onlycap != skp)
- return -EPERM;
-
data = kzalloc(count + 1, GFP_KERNEL);
if (data == NULL)
return -ENOMEM;

if (copy_from_user(data, buf, count) != 0) {
- rc = -EFAULT;
- goto freeout;
+ kfree(data);
+ return -EFAULT;
+ }
+
+ data_parse = data;
+ while ((tok = strsep(&data_parse, " ")) != NULL) {
+ if (!*tok)
+ continue;
+
+ skp = smk_import_entry(tok, 0);
+ if (IS_ERR(skp)) {
+ rc = PTR_ERR(skp);
+ break;
+ }
+
+ sop = kzalloc(sizeof(*sop), GFP_KERNEL);
+ if (sop == NULL) {
+ rc = -ENOMEM;
+ break;
+ }
+
+ sop->smk_label = skp;
+ list_add_rcu(&sop->list, &list_tmp);
}
+ kfree(data);

/*
* Clear the smack_onlycap on invalid label errors. This means
@@ -1710,26 +1763,29 @@ static ssize_t smk_write_onlycap(struct file *file, const char __user *buf,
* so "-usecapabilities" will also work.
*
* But do so only on invalid label, not on system errors.
+ * The invalid label must be first to count as clearing attempt.
*/
- skp = smk_import_entry(data, count);
- if (PTR_ERR(skp) == -EINVAL)
- skp = NULL;
- else if (IS_ERR(skp)) {
- rc = PTR_ERR(skp);
- goto freeout;
+ if (rc == -EINVAL && list_empty(&list_tmp))
+ rc = count;
+
+ if (rc >= 0) {
+ mutex_lock(&smack_onlycap_lock);
+ list_swap_rcu(&smack_onlycap_list, &list_tmp);
+ mutex_unlock(&smack_onlycap_lock);
}

- smack_onlycap = skp;
+ list_for_each_entry_safe(sop, sop2, &list_tmp, list)
+ kfree(sop);

-freeout:
- kfree(data);
return rc;
}

static const struct file_operations smk_onlycap_ops = {
- .read = smk_read_onlycap,
+ .open = smk_open_onlycap,
+ .read = seq_read,
.write = smk_write_onlycap,
- .llseek = default_llseek,
+ .llseek = seq_lseek,
+ .release = seq_release,
};

#ifdef CONFIG_SECURITY_SMACK_BRINGUP
--
2.1.4

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