[RFC][PATCH] Smack<->Audit integration

Ahmed S. Darwish
2008-03-10T12:49:28Z

Hi all,

This is the second step of integrating Audit with Smack.

The AUDIT_SUBJ_USER and AUDIT_OBJ_USER SELinux flags are recycled
for Smack to avoid `auditd' userspace modifications. Smack only
needs auditing on subject/object bases, so those flags were enough.

Patch below setups the new Audit LSM hooks and add a secid field in
smack inode and ipc security structures. The secid field was needed
cause it's the main Audit way of distinguishing kernel objects to
be audited from the remaining ones.

Possibly the last steps would be to:
1- report smack access grants and denials through Audit (like AVC)
2- Letting Audit send an OBJ_USER event in case of a process that
recieved a signal without affecting SELinux.

Thank you for your reviews.

Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com>
---

smack.h | 9 ++
smack_lsm.c | 211 +++++++++++++++++++++++++++++++++++++++++++++++++++++-----

2 files changed, 200 insertions(+), 17 deletions(-)

Patch is generated over James security/next branch cause it's the
only tree that currently has the Audit hooks merged:
git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/security-testing-2.6.git#next

diff --git a/security/smack/smack.h b/security/smack/smack.h
index c444f48..2c8bb4c 100644
--- a/security/smack/smack.h
+++ b/security/smack/smack.h
@@ -57,6 +57,15 @@ struct inode_smack {
char *smk_inode; /* label of the fso */
struct mutex smk_lock; /* initialization lock */
int smk_flags; /* smack inode flags */
+ int secid; /* security identifier */
+};
+
+/*
+ * IPC smack data
+ */
+struct ipc_smack {
+ char *smk_ipc; /* ipc object label */
+ int secid; /* security identifier */
};

#define SMK_INODE_INSTANT 0x01 /* inode is instantiated */
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index afa7967..5b5e1fd 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -6,6 +6,9 @@
* Author:
* Casey Schaufler <casey@schaufler-ca.com>
*
+ * Audit integration by:
+ * Ahmed S. Darwish <darwish.07@gmail.com>
+ *
* Copyright (C) 2007 Casey Schaufler <casey@schaufler-ca.com>
*
* This program is free software; you can redistribute it and/or modify
@@ -24,6 +27,7 @@
#include <linux/udp.h>
#include <linux/mutex.h>
#include <linux/pipe_fs_i.h>
+#include <linux/audit.h>
#include <net/netlabel.h>
#include <net/cipso_ipv4.h>

@@ -75,6 +79,7 @@ struct inode_smack *new_inode_smack(char *smack)

isp->smk_inode = smack;
isp->smk_flags = 0;
+ isp->secid = smack_to_secid(smack);
mutex_init(&isp->smk_lock);

return isp;
@@ -638,6 +643,8 @@ static void smack_inode_post_setxattr(struct dentry *dentry, char *name,
else
isp->smk_inode = smack_known_invalid.smk_known;

+ isp->secid = smack_to_secid(isp->smk_inode);
+
return;
}

@@ -759,6 +766,17 @@ static int smack_inode_listsecurity(struct inode *inode, char *buffer,
return -EINVAL;
}

+/**
+ * smack_inode_getsecid - Extract inode's security id
+ * @inode: inode to extract the info from
+ * @secid: where the result will be saved
+ */
+static void smack_inode_getsecid(const struct inode *inode, u32 *secid)
+{
+ struct inode_smack *isp = inode->i_security;
+ *secid = isp->secid;
+}
+
/*
* File Hooks
*/
@@ -1344,6 +1362,7 @@ static int smack_inode_setsecurity(struct inode *inode, const char *name,
const void *value, size_t size, int flags)
{
char *sp;
+ struct smack_known *skp;
struct inode_smack *nsp = inode->i_security;
struct socket_smack *ssp;
struct socket *sock;
@@ -1352,12 +1371,14 @@ static int smack_inode_setsecurity(struct inode *inode, const char *name,
if (value == NULL || size > SMK_LABELLEN)
return -EACCES;

- sp = smk_import(value, size);
- if (sp == NULL)
+ skp = smk_import_entry(value, size);
+ if (skp == NULL)
return -EINVAL;

+ sp = skp->smk_known;
if (strcmp(name, XATTR_SMACK_SUFFIX) == 0) {
nsp->smk_inode = sp;
+ nsp->secid = skp->smk_secid;
return 0;
}
/*
@@ -1471,9 +1492,16 @@ static char *smack_of_shm(struct shmid_kernel *shp)
*/
static int smack_shm_alloc_security(struct shmid_kernel *shp)
{
- struct kern_ipc_perm *isp = &shp->shm_perm;
+ struct ipc_smack *isp;
+ struct kern_ipc_perm *ipcp = &shp->shm_perm;

- isp->security = current->security;
+ isp = kzalloc(sizeof(struct ipc_smack), GFP_KERNEL);
+ if (isp == NULL)
+ return -ENOMEM;
+
+ isp->smk_ipc = current->security;
+ isp->secid = smack_to_secid(isp->smk_ipc);
+ ipcp->security = isp;
return 0;
}

@@ -1485,9 +1513,9 @@ static int smack_shm_alloc_security(struct shmid_kernel *shp)
*/
static void smack_shm_free_security(struct shmid_kernel *shp)
{
- struct kern_ipc_perm *isp = &shp->shm_perm;
+ struct kern_ipc_perm *ipcp = &shp->shm_perm;

- isp->security = NULL;
+ kfree(ipcp->security);
}

/**
@@ -1579,9 +1607,16 @@ static char *smack_of_sem(struct sem_array *sma)
*/
static int smack_sem_alloc_security(struct sem_array *sma)
{
- struct kern_ipc_perm *isp = &sma->sem_perm;
+ struct ipc_smack *isp;
+ struct kern_ipc_perm *ipcp = &sma->sem_perm;
+
+ isp = kzalloc(sizeof(struct ipc_smack), GFP_KERNEL);
+ if (isp == NULL)
+ return -ENOMEM;

- isp->security = current->security;
+ isp->smk_ipc = current->security;
+ isp->secid = smack_to_secid(isp->smk_ipc);
+ ipcp->security = isp;
return 0;
}

@@ -1595,7 +1630,7 @@ static void smack_sem_free_security(struct sem_array *sma)
{
struct kern_ipc_perm *isp = &sma->sem_perm;

- isp->security = NULL;
+ kfree(isp->security);
}

/**
@@ -1682,9 +1717,16 @@ static int smack_sem_semop(struct sem_array *sma, struct sembuf *sops,
*/
static int smack_msg_queue_alloc_security(struct msg_queue *msq)
{
- struct kern_ipc_perm *kisp = &msq->q_perm;
+ struct ipc_smack *isp;
+ struct kern_ipc_perm *ipcp = &msq->q_perm;

- kisp->security = current->security;
+ isp = kzalloc(sizeof(struct ipc_smack), GFP_KERNEL);
+ if (isp == NULL)
+ return -ENOMEM;
+
+ isp->smk_ipc = current->security;
+ isp->secid = smack_to_secid(isp->smk_ipc);
+ ipcp->security = isp;
return 0;
}

@@ -1696,9 +1738,9 @@ static int smack_msg_queue_alloc_security(struct msg_queue *msq)
*/
static void smack_msg_queue_free_security(struct msg_queue *msq)
{
- struct kern_ipc_perm *kisp = &msq->q_perm;
+ struct kern_ipc_perm *ipcp = &msq->q_perm;

- kisp->security = NULL;
+ kfree(ipcp->security);
}

/**
@@ -1800,18 +1842,30 @@ static int smack_msg_queue_msgrcv(struct msg_queue *msq, struct msg_msg *msg,

/**
* smack_ipc_permission - Smack access for ipc_permission()
- * @ipp: the object permissions
+ * @ipcp: the object permissions
* @flag: access requested
*
* Returns 0 if current has read and write access, error code otherwise
*/
-static int smack_ipc_permission(struct kern_ipc_perm *ipp, short flag)
+static int smack_ipc_permission(struct kern_ipc_perm *ipcp, short flag)
{
- char *isp = ipp->security;
int may;
+ struct ipc_smack *isp = ipcp->security;

may = smack_flags_to_may(flag);
- return smk_curacc(isp, may);
+ return smk_curacc(isp->smk_ipc, may);
+}
+
+/**
+ * smack_ipc_getsecid - extract Smack security id
+ * @ipcp: the object permissions
+ * @secid: where result will be saved
+ */
+static void smack_ipc_getsecid(struct kern_ipc_perm *ipcp, u32 *secid)
+{
+ struct inode_smack *isp = ipcp->security;
+
+ *secid = isp->secid;
}

/* module stacking operations */
@@ -1967,6 +2021,7 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
else
isp->smk_inode = final;

+ isp->secid = smack_to_secid(isp->smk_inode);
isp->smk_flags |= SMK_INODE_INSTANT;

unlockandout:
@@ -2391,6 +2446,116 @@ static int smack_key_permission(key_ref_t key_ref,
#endif /* CONFIG_KEYS */

/*
+ * Smack Audit hooks
+ *
+ * Audit requires an internal representation of each Smack specific
+ * rule which works as a glue between the audit hooks. Since smack_known
+ * repository entries are added but never deleted, we'll use the
+ * smack_known entry related to the given audit rule as the needed
+ * smack representation.
+ *
+ * This will also save us from searching the smack labels repository
+ * each time the audit_rule_match hook get called.
+ */
+#ifdef CONFIG_AUDIT
+
+/**
+ * smack_audit_rule_init - Initialize a smack audit rule
+ * @field: Message flags given from user-space (audit.h)
+ * @op: Required operation (Only equality testing is allowed)
+ * @rulestr: Given user-space rule
+ * @vrule: Where we'll save our own audit rule representation
+ *
+ * The label to be audited (rulestr) is created if necessay
+ */
+static int smack_audit_rule_init(u32 field, u32 op, char *rulestr, void **vrule)
+{
+ struct smack_known **smk_rule = (struct smack_known **)vrule;
+ *smk_rule = NULL;
+
+ if (field != AUDIT_SUBJ_USER && field != AUDIT_OBJ_USER)
+ return -EINVAL;
+
+ if (op != AUDIT_EQUAL && op != AUDIT_NOT_EQUAL)
+ return -EINVAL;
+
+ *smk_rule = smk_import_entry(rulestr, 0);
+
+ return 0;
+}
+
+/**
+ * smack_audit_rule_known - Distinguish smack audit rules from others
+ * @krule: rule of interest, in internal kernel representation format
+ *
+ * This is used to filter rules related to Smack from other saved
+ * Audit rules. If it's proved that this rule belongs to us, the
+ * audit_rule_match hook will be used to check a specific kernel
+ * object against its smack audit rule.
+ */
+static int smack_audit_rule_known(struct audit_krule *krule)
+{
+ struct audit_field *f;
+ int i;
+
+ for (i = 0; i < krule->field_count; i++) {
+ f = &krule->fields[i];
+
+ if (f->type == AUDIT_SUBJ_USER || f->type == AUDIT_OBJ_USER)
+ return 1;
+ }
+
+ return 0;
+}
+
+/**
+ * smack_audit_rule_match - Audit given secid identified object ?
+ * @secid: Security id to test
+ * @field: Message flags given from user-space
+ * @op: Required operation (only equality is allowed)
+ * @vrule: Smack audit rule that will be checked against the secid object
+ * @actx: audit context associated with the check (used for Audit logging)
+ *
+ * This is the core Audit hook. It's used to identify objects like
+ * syscalls and inodes requested from user-space to be audited from
+ * remaining kernel objects.
+ */
+static int smack_audit_rule_match(u32 secid, u32 field, u32 op, void *vrule,
+ struct audit_context *actx)
+{
+ struct smack_known *smk_rule = vrule;
+
+ if (!smk_rule) {
+ audit_log(actx, GFP_KERNEL, AUDIT_SELINUX_ERR,
+ "Smack: missing rule\n");
+ return -ENOENT;
+ }
+
+ if (field != AUDIT_SUBJ_USER && field != AUDIT_OBJ_USER)
+ return 0;
+
+ if (op == AUDIT_EQUAL)
+ return (smk_rule->smk_secid == secid);
+ if (op == AUDIT_NOT_EQUAL)
+ return (smk_rule->smk_secid != secid);
+
+ return 0;
+}
+
+/**
+ * smack_audit_rule_free - free internal audit rule representation
+ * @vrule: rule to be freed.
+ *
+ * No memory was allocated in audit_rule_init.
+ */
+static void smack_audit_rule_free(void *vrule)
+{
+ /* No-op */
+}
+
+#endif /* CONFIG_AUDIT */
+
+/*
* smack_secid_to_secctx - return the smack label for a secid
* @secid: incoming integer
* @secdata: destination
@@ -2476,6 +2641,7 @@ struct security_operations smack_ops = {
.inode_getsecurity = smack_inode_getsecurity,
.inode_setsecurity = smack_inode_setsecurity,
.inode_listsecurity = smack_inode_listsecurity,
+ .inode_getsecid = smack_inode_getsecid,

.file_permission = smack_file_permission,
.file_alloc_security = smack_file_alloc_security,
@@ -2506,6 +2672,7 @@ struct security_operations smack_ops = {
.task_to_inode = smack_task_to_inode,

.ipc_permission = smack_ipc_permission,
+ .ipc_getsecid = smack_ipc_getsecid,

.msg_msg_alloc_security = smack_msg_msg_alloc_security,
.msg_msg_free_security = smack_msg_msg_free_security,
@@ -2550,12 +2717,22 @@ struct security_operations smack_ops = {
.sk_free_security = smack_sk_free_security,
.sock_graft = smack_sock_graft,
.inet_conn_request = smack_inet_conn_request,
+
/* key management security hooks */
#ifdef CONFIG_KEYS
.key_alloc = smack_key_alloc,
.key_free = smack_key_free,
.key_permission = smack_key_permission,
#endif /* CONFIG_KEYS */
+
+ /* Audit hooks */
+#ifdef CONFIG_AUDIT
+ .audit_rule_init = smack_audit_rule_init,
+ .audit_rule_known = smack_audit_rule_known,
+ .audit_rule_match = smack_audit_rule_match,
+ .audit_rule_free = smack_audit_rule_free,
+#endif /* CONFIG_AUDIT */
+
.secid_to_secctx = smack_secid_to_secctx,
.secctx_to_secid = smack_secctx_to_secid,
.release_secctx = smack_release_secctx,

Regards,

--

"Better to light a candle, than curse the darkness"

Ahmed S. Darwish
Homepage: http://darwish.07.googlepages.com
Blog: http://darwish-07.blogspot.com