Re: [RFC][PATCH -v2] Smack: Integrate with Audit

Casey Schaufler
2008-03-12T04:23:13Z

--- "Ahmed S. Darwish" <darwish.07@gmail.com> wrote:

> Hi!,
>
> Setup the new Audit hooks for Smack. The AUDIT_SUBJ_USER and
> AUDIT_OBJ_USER SELinux flags are recycled to avoid `auditd'
> userspace modifications. Smack only needs auditing on
> a subject/object bases, so those flags were enough.
>
> Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com>
> ---
>
> smack_lsm.c | 153 ++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 153 insertions(+)
>
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index afa7967..d471839 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -26,6 +26,7 @@
> #include <linux/pipe_fs_i.h>
> #include <net/netlabel.h>
> #include <net/cipso_ipv4.h>
> +#include <linux/audit.h>
>
> #include "smack.h"
>
> @@ -759,6 +760,17 @@ 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 result will be saved
> + */
> +static void smack_inode_getsecid(const struct inode *inode, u32 *secid)
> +{
> + struct inode_smack *isp = inode->i_security;

How about a blank line between the declareations and the code?

> + *secid = smack_to_secid(isp->smk_inode);
> +}
> +
> /*
> * File Hooks
> */
> @@ -1814,6 +1826,17 @@ static int smack_ipc_permission(struct kern_ipc_perm
> *ipp, short flag)
> return smk_curacc(isp, may);
> }
>
> +/**
> + * smack_ipc_getsecid - Extract ipc object security id
> + * @ipp: the object permissions
> + * @secid: where result will be saved
> + */
> +static void smack_ipc_getsecid(struct kern_ipc_perm *ipp, u32 *secid)
> +{
> + char *smack = ipp->security;

Blank line

> + *secid = smack_to_secid(smack);
> +}
> +
> /* module stacking operations */
>
> /**
> @@ -2391,6 +2414,124 @@ static int smack_key_permission(key_ref_t key_ref,
> #endif /* CONFIG_KEYS */
>
> /*
> + * Smack Audit hooks
> + *
> + * Audit requires a unique representation of each Smack specific
> + * rule. This unique representation is used to distinguish the
> + * object to be audited from remaining kernel objects and also
> + * works as a glue between the audit hooks.
> + *
> + * Since repository entries are added but never deleted, we'll use
> + * the smack_known label address related to the given audit rule as
> + * the needed unique representation. This also better fits the smack
> + * model where nearly everything is a label.
> + */
> +#ifdef CONFIG_AUDIT
> +
> +/**
> + * smack_audit_rule_init - Initialize a smack audit rule
> + * @field: audit rule fields given from user-space (audit.h)
> + * @op: required testing operator (=, !=, >, <, ...)

We could say that label1 > label2 if a subject with label1 can
read an object with label2, and that label3 < label4 if a subject
with label3 cannot read an object with label4. But that's pretty
arbitrary. Let's leave it as you have it, at least for now.

> + * @rulestr: smack label to be audited
> + * @vrule: pointer to save our own audit rule representation
> + *
> + * Prepare to audit cases where (@field @op @rulestr) is true.
> + * The label to be audited is created if necessay.
> + */
> +static int smack_audit_rule_init(u32 field, u32 op, char *rulestr, void
> **vrule)
> +{
> + char **rule = (char **)vrule;
> + *rule = NULL;
> +
> + if (field != AUDIT_SUBJ_USER && field != AUDIT_OBJ_USER)
> + return -EINVAL;
> +
> + if (op != AUDIT_EQUAL && op != AUDIT_NOT_EQUAL)
> + return -EINVAL;
> +
> + *rule = smk_import(rulestr, 0);
> +
> + return 0;
> +}
> +
> +/**
> + * smack_audit_rule_known - Distinguish Smack audit rules
> + * @krule: rule of interest, in Audit kernel representation format
> + *
> + * This is used to filter Smack rules from remaining Audit ones.
> + * If it's proved that this rule belongs to us, the
> + * audit_rule_match hook will be called to do the final judgement.
> + */
> +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 object ?
> + * @secid: security id for identifying the object to test
> + * @field: audit rule flags given from user-space
> + * @op: required testing operator
> + * @vrule: smack internal rule presentation
> + * @actx: audit context associated with the check
> + *
> + * The core Audit hook. It's used to take the decision of
> + * whether to audit or not to audit a given object.
> + */
> +static int smack_audit_rule_match(u32 secid, u32 field, u32 op, void *vrule,
> + struct audit_context *actx)
> +{
> + char *smack;
> + char *rule = vrule;
> +
> + if (!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;
> +
> + smack = smack_from_secid(secid);
> +
> + /*
> + * No need to do string comparisons since we're sure
> + * that if a match occurs, both pointers will point
> + * to the same smack_konwn label.

smack_known, not smack_konwn. Must be getting early there.

> + */
> + if (op == AUDIT_EQUAL)
> + return (rule == smack);
> + if (op == AUDIT_NOT_EQUAL)
> + return (rule != smack);
> +
> + return 0;
> +}
> +
> +/**
> + * smack_audit_rule_free - free smack rule representation
> + * @vrule: rule to be freed.
> + *
> + * No memory was allocated.
> + */
> +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 +2617,7 @@ 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 +2648,7 @@ 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 +2693,22 @@ 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,
>
> --
>
> "Better to light a candle, than curse the darkness"
>
> Ahmed S. Darwish
> Homepage: http://darwish.07.googlepages.com
> Blog: http://darwish-07.blogspot.com

Casey Schaufler
casey@schaufler-ca.com