Date:	Tue, 15 Jan 2013 19:26:20 -0800
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	Rafal Krypa <r.krypa@...sung.com>
CC:	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCHv2] Smack: add support for modification of existing rules

On 1/10/2013 10:42 AM, Rafal Krypa wrote:
> Rule modifications are enabled via /smack/change-rule. Format is as follows:
> "Subject Object rwaxt rwaxt"
>
> First two strings are subject and object labels up to 255 characters.
> Third string contains permissions to enable.
> Fourth string contains permissions to disable.
>
> All unmentioned permissions will be left unchanged.
> If no rule previously existed, it will be created.
>
> Targeted for git://git.gitorious.org/smack-next/kernel.git

Applied to git://git.gitorious.org/smack-next/kernel.git#stage-for-3.9


>
> Signed-off-by: Rafal Krypa <r.krypa@...sung.com>
> ---
>  Documentation/security/Smack.txt |   11 ++
>  security/smack/smackfs.c         |  249 ++++++++++++++++++++++++++------------
>  2 files changed, 181 insertions(+), 79 deletions(-)
>
> diff --git a/Documentation/security/Smack.txt b/Documentation/security/Smack.txt
> index 8a177e4..7a2d30c 100644
> --- a/Documentation/security/Smack.txt
> +++ b/Documentation/security/Smack.txt
> @@ -117,6 +117,17 @@ access2
>  ambient
>  	This contains the Smack label applied to unlabeled network
>  	packets.
> +change-rule
> +	This interface allows modification of existing access control rules.
> +	The format accepted on write is:
> +		"%s %s %s %s"
> +	where the first string is the subject label, the second the
> +	object label, the third the access to allow and the fourth the
> +	access to deny. The access strings may contain only the characters
> +	"rwxat-". If a rule for a given subject and object exists it will be
> +	modified by enabling the permissions in the third string and disabling
> +	those in the fourth string. If there is no such rule it will be
> +	created using the access specified in the third and the fourth strings.
>  cipso
>  	This interface allows a specific CIPSO header to be assigned
>  	to a Smack label. The format accepted on write is:
> diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
> index 337e32c..2479a41 100644
> --- a/security/smack/smackfs.c
> +++ b/security/smack/smackfs.c
> @@ -50,12 +50,12 @@ enum smk_inos {
>  	SMK_ACCESS2	= 16,	/* make an access check with long labels */
>  	SMK_CIPSO2	= 17,	/* load long label -> CIPSO mapping */
>  	SMK_REVOKE_SUBJ	= 18,	/* set rules with subject label to '-' */
> +	SMK_CHANGE_RULE	= 19,	/* change or add rules (long labels) */
>  };
>  
>  /*
>   * List locks
>   */
> -static DEFINE_MUTEX(smack_list_lock);
>  static DEFINE_MUTEX(smack_cipso_lock);
>  static DEFINE_MUTEX(smack_ambient_lock);
>  static DEFINE_MUTEX(smk_netlbladdr_lock);
> @@ -110,6 +110,13 @@ struct smack_master_list {
>  
>  LIST_HEAD(smack_rule_list);
>  
> +struct smack_parsed_rule {
> +	char			*smk_subject;
> +	char			*smk_object;
> +	int			smk_access1;
> +	int			smk_access2;
> +};
> +
>  static int smk_cipso_doi_value = SMACK_CIPSO_DOI_DEFAULT;
>  
>  const char *smack_cipso_option = SMACK_CIPSO_OPTION;
> @@ -167,25 +174,28 @@ static void smk_netlabel_audit_set(struct netlbl_audit *nap)
>  #define SMK_NETLBLADDRMIN	9
>  
>  /**
> - * smk_set_access - add a rule to the rule list
> - * @srp: the new rule to add
> + * smk_set_access - add a rule to the rule list or replace an old rule
> + * @srp: the rule to add or replace
>   * @rule_list: the list of rules
>   * @rule_lock: the rule list lock
> + * @global: if non-zero, indicates a global rule
>   *
>   * Looks through the current subject/object/access list for
>   * the subject/object pair and replaces the access that was
>   * there. If the pair isn't found add it with the specified
>   * access.
>   *
> - * Returns 1 if a rule was found to exist already, 0 if it is new
>   * Returns 0 if nothing goes wrong or -ENOMEM if it fails
>   * during the allocation of the new pair to add.
>   */
> -static int smk_set_access(struct smack_rule *srp, struct list_head *rule_list,
> -				struct mutex *rule_lock)
> +static int smk_set_access(struct smack_parsed_rule *srp,
> +				struct list_head *rule_list,
> +				struct mutex *rule_lock, int global)
>  {
>  	struct smack_rule *sp;
> +	struct smack_master_list *smlp;
>  	int found = 0;
> +	int rc = 0;
>  
>  	mutex_lock(rule_lock);
>  
> @@ -197,23 +207,89 @@ static int smk_set_access(struct smack_rule *srp, struct list_head *rule_list,
>  		if (sp->smk_object == srp->smk_object &&
>  		    sp->smk_subject == srp->smk_subject) {
>  			found = 1;
> -			sp->smk_access = srp->smk_access;
> +			sp->smk_access |= srp->smk_access1;
> +			sp->smk_access &= ~srp->smk_access2;
>  			break;
>  		}
>  	}
> -	if (found == 0)
> -		list_add_rcu(&srp->list, rule_list);
>  
> +	if (found == 0) {
> +		sp = kzalloc(sizeof(*sp), GFP_KERNEL);
> +		if (sp == NULL) {
> +			rc = -ENOMEM;
> +			goto out;
> +		}
> +
> +		sp->smk_subject = srp->smk_subject;
> +		sp->smk_object = srp->smk_object;
> +		sp->smk_access = srp->smk_access1 & ~srp->smk_access2;
> +
> +		list_add_rcu(&sp->list, rule_list);
> +		/*
> +		 * If this is a global as opposed to self and a new rule
> +		 * it needs to get added for reporting.
> +		 */
> +		if (global) {
> +			smlp = kzalloc(sizeof(*smlp), GFP_KERNEL);
> +			if (smlp != NULL) {
> +				smlp->smk_rule = sp;
> +				list_add_rcu(&smlp->list, &smack_rule_list);
> +			} else
> +				rc = -ENOMEM;
> +		}
> +	}
> +
> +out:
>  	mutex_unlock(rule_lock);
> +	return rc;
> +}
> +
> +/**
> + * smk_perm_from_str - parse smack accesses from a text string
> + * @string: a text string that contains a Smack accesses code
> + *
> + * Returns an integer with respective bits set for specified accesses.
> + */
> +static int smk_perm_from_str(const char *string)
> +{
> +	int perm = 0;
> +	const char *cp;
>  
> -	return found;
> +	for (cp = string; ; cp++)
> +		switch (*cp) {
> +		case '-':
> +			break;
> +		case 'r':
> +		case 'R':
> +			perm |= MAY_READ;
> +			break;
> +		case 'w':
> +		case 'W':
> +			perm |= MAY_WRITE;
> +			break;
> +		case 'x':
> +		case 'X':
> +			perm |= MAY_EXEC;
> +			break;
> +		case 'a':
> +		case 'A':
> +			perm |= MAY_APPEND;
> +			break;
> +		case 't':
> +		case 'T':
> +			perm |= MAY_TRANSMUTE;
> +			break;
> +		default:
> +			return perm;
> +		}
>  }
>  
>  /**
>   * smk_fill_rule - Fill Smack rule from strings
>   * @subject: subject label string
>   * @object: object label string
> - * @access: access string
> + * @access1: access string
> + * @access2: string with permissions to be removed
>   * @rule: Smack rule
>   * @import: if non-zero, import labels
>   * @len: label length limit
> @@ -221,8 +297,9 @@ static int smk_set_access(struct smack_rule *srp, struct list_head *rule_list,
>   * Returns 0 on success, -1 on failure
>   */
>  static int smk_fill_rule(const char *subject, const char *object,
> -				const char *access, struct smack_rule *rule,
> -				int import, int len)
> +				const char *access1, const char *access2,
> +				struct smack_parsed_rule *rule, int import,
> +				int len)
>  {
>  	const char *cp;
>  	struct smack_known *skp;
> @@ -255,36 +332,11 @@ static int smk_fill_rule(const char *subject, const char *object,
>  		rule->smk_object = skp->smk_known;
>  	}
>  
> -	rule->smk_access = 0;
> -
> -	for (cp = access; *cp != '\0'; cp++) {
> -		switch (*cp) {
> -		case '-':
> -			break;
> -		case 'r':
> -		case 'R':
> -			rule->smk_access |= MAY_READ;
> -			break;
> -		case 'w':
> -		case 'W':
> -			rule->smk_access |= MAY_WRITE;
> -			break;
> -		case 'x':
> -		case 'X':
> -			rule->smk_access |= MAY_EXEC;
> -			break;
> -		case 'a':
> -		case 'A':
> -			rule->smk_access |= MAY_APPEND;
> -			break;
> -		case 't':
> -		case 'T':
> -			rule->smk_access |= MAY_TRANSMUTE;
> -			break;
> -		default:
> -			return 0;
> -		}
> -	}
> +	rule->smk_access1 = smk_perm_from_str(access1);
> +	if (access2)
> +		rule->smk_access2 = smk_perm_from_str(access2);
> +	else
> +		rule->smk_access2 = ~rule->smk_access1;
>  
>  	return 0;
>  }
> @@ -297,30 +349,33 @@ static int smk_fill_rule(const char *subject, const char *object,
>   *
>   * Returns 0 on success, -1 on errors.
>   */
> -static int smk_parse_rule(const char *data, struct smack_rule *rule, int import)
> +static int smk_parse_rule(const char *data, struct smack_parsed_rule *rule,
> +				int import)
>  {
>  	int rc;
>  
>  	rc = smk_fill_rule(data, data + SMK_LABELLEN,
> -			   data + SMK_LABELLEN + SMK_LABELLEN, rule, import,
> -			   SMK_LABELLEN);
> +			   data + SMK_LABELLEN + SMK_LABELLEN, NULL, rule,
> +			   import, SMK_LABELLEN);
>  	return rc;
>  }
>  
>  /**
>   * smk_parse_long_rule - parse Smack rule from rule string
>   * @data: string to be parsed, null terminated
> - * @rule: Smack rule
> + * @rule: Will be filled with Smack parsed rule
>   * @import: if non-zero, import labels
> + * @change: if non-zero, data is from /smack/change-rule
>   *
>   * Returns 0 on success, -1 on failure
>   */
> -static int smk_parse_long_rule(const char *data, struct smack_rule *rule,
> -				int import)
> +static int smk_parse_long_rule(const char *data, struct smack_parsed_rule *rule,
> +				int import, int change)
>  {
>  	char *subject;
>  	char *object;
> -	char *access;
> +	char *access1;
> +	char *access2;
>  	int datalen;
>  	int rc = -1;
>  
> @@ -334,14 +389,27 @@ static int smk_parse_long_rule(const char *data, struct smack_rule *rule,
>  	object = kzalloc(datalen, GFP_KERNEL);
>  	if (object == NULL)
>  		goto free_out_s;
> -	access = kzalloc(datalen, GFP_KERNEL);
> -	if (access == NULL)
> +	access1 = kzalloc(datalen, GFP_KERNEL);
> +	if (access1 == NULL)
>  		goto free_out_o;
> +	access2 = kzalloc(datalen, GFP_KERNEL);
> +	if (access2 == NULL)
> +		goto free_out_a;
> +
> +	if (change) {
> +		if (sscanf(data, "%s %s %s %s",
> +			subject, object, access1, access2) == 4)
> +			rc = smk_fill_rule(subject, object, access1, access2,
> +				rule, import, 0);
> +	} else {
> +		if (sscanf(data, "%s %s %s", subject, object, access1) == 3)
> +			rc = smk_fill_rule(subject, object, access1, NULL,
> +				rule, import, 0);
> +	}
>  
> -	if (sscanf(data, "%s %s %s", subject, object, access) == 3)
> -		rc = smk_fill_rule(subject, object, access, rule, import, 0);
> -
> -	kfree(access);
> +	kfree(access2);
> +free_out_a:
> +	kfree(access1);
>  free_out_o:
>  	kfree(object);
>  free_out_s:
> @@ -351,6 +419,7 @@ free_out_s:
>  
>  #define SMK_FIXED24_FMT	0	/* Fixed 24byte label format */
>  #define SMK_LONG_FMT	1	/* Variable long label format */
> +#define SMK_CHANGE_FMT	2	/* Rule modification format */
>  /**
>   * smk_write_rules_list - write() for any /smack rule file
>   * @file: file pointer, not actually used
> @@ -359,22 +428,24 @@ free_out_s:
>   * @ppos: where to start - must be 0
>   * @rule_list: the list of rules to write to
>   * @rule_lock: lock for the rule list
> - * @format: /smack/load or /smack/load2 format.
> + * @format: /smack/load or /smack/load2 or /smack/change-rule format.
>   *
>   * Get one smack access rule from above.
>   * The format for SMK_LONG_FMT is:
>   *	"subject<whitespace>object<whitespace>access[<whitespace>...]"
>   * The format for SMK_FIXED24_FMT is exactly:
>   *	"subject                 object                  rwxat"
> + * The format for SMK_CHANGE_FMT is:
> + *	"subject<whitespace>object<whitespace>
> + *	 acc_enable<whitespace>acc_disable[<whitespace>...]"
>   */
>  static ssize_t smk_write_rules_list(struct file *file, const char __user *buf,
>  					size_t count, loff_t *ppos,
>  					struct list_head *rule_list,
>  					struct mutex *rule_lock, int format)
>  {
> -	struct smack_master_list *smlp;
>  	struct smack_known *skp;
> -	struct smack_rule *rule;
> +	struct smack_parsed_rule *rule;
>  	char *data;
>  	int datalen;
>  	int rc = -EINVAL;
> @@ -417,7 +488,11 @@ static ssize_t smk_write_rules_list(struct file *file, const char __user *buf,
>  		 * Be sure the data string is terminated.
>  		 */
>  		data[count] = '\0';
> -		if (smk_parse_long_rule(data, rule, 1))
> +		if (smk_parse_long_rule(data, rule, 1, 0))
> +			goto out_free_rule;
> +	} else if (format == SMK_CHANGE_FMT) {
> +		data[count] = '\0';
> +		if (smk_parse_long_rule(data, rule, 1, 1))
>  			goto out_free_rule;
>  	} else {
>  		/*
> @@ -437,22 +512,9 @@ static ssize_t smk_write_rules_list(struct file *file, const char __user *buf,
>  		rule_lock = &skp->smk_rules_lock;
>  	}
>  
> -	rc = count;
> -	/*
> -	 * If this is a global as opposed to self and a new rule
> -	 * it needs to get added for reporting.
> -	 * smk_set_access returns true if there was already a rule
> -	 * for the subject/object pair, and false if it was new.
> -	 */
> -	if (!smk_set_access(rule, rule_list, rule_lock)) {
> -		if (load) {
> -			smlp = kzalloc(sizeof(*smlp), GFP_KERNEL);
> -			if (smlp != NULL) {
> -				smlp->smk_rule = rule;
> -				list_add_rcu(&smlp->list, &smack_rule_list);
> -			} else
> -				rc = -ENOMEM;
> -		}
> +	rc = smk_set_access(rule, rule_list, rule_lock, load);
> +	if (rc == 0) {
> +		rc = count;
>  		goto out;
>  	}
>  
> @@ -1774,7 +1836,7 @@ static const struct file_operations smk_load_self_ops = {
>  static ssize_t smk_user_access(struct file *file, const char __user *buf,
>  				size_t count, loff_t *ppos, int format)
>  {
> -	struct smack_rule rule;
> +	struct smack_parsed_rule rule;
>  	char *data;
>  	char *cod;
>  	int res;
> @@ -1796,14 +1858,14 @@ static ssize_t smk_user_access(struct file *file, const char __user *buf,
>  			return -ENOMEM;
>  		memcpy(cod, data, count);
>  		cod[count] = '\0';
> -		res = smk_parse_long_rule(cod, &rule, 0);
> +		res = smk_parse_long_rule(cod, &rule, 0, 0);
>  		kfree(cod);
>  	}
>  
>  	if (res)
>  		return -EINVAL;
>  
> -	res = smk_access(rule.smk_subject, rule.smk_object, rule.smk_access,
> +	res = smk_access(rule.smk_subject, rule.smk_object, rule.smk_access1,
>  			  NULL);
>  	data[0] = res == 0 ? '1' : '0';
>  	data[1] = '\0';
> @@ -2075,6 +2137,33 @@ static int smk_init_sysfs(void)
>  }
>  
>  /**
> + * smk_write_change_rule - write() for /smack/change-rule
> + * @file: file pointer
> + * @buf: data from user space
> + * @count: bytes sent
> + * @ppos: where to start - must be 0
> + */
> +static ssize_t smk_write_change_rule(struct file *file, const char __user *buf,
> +				size_t count, loff_t *ppos)
> +{
> +	/*
> +	 * Must have privilege.
> +	 */
> +	if (!capable(CAP_MAC_ADMIN))
> +		return -EPERM;
> +
> +	return smk_write_rules_list(file, buf, count, ppos, NULL, NULL,
> +				    SMK_CHANGE_FMT);
> +}
> +
> +static const struct file_operations smk_change_rule_ops = {
> +	.write		= smk_write_change_rule,
> +	.read		= simple_transaction_read,
> +	.release	= simple_transaction_release,
> +	.llseek		= generic_file_llseek,
> +};
> +
> +/**
>   * smk_fill_super - fill the /smackfs superblock
>   * @sb: the empty superblock
>   * @data: unused
> @@ -2123,6 +2212,8 @@ static int smk_fill_super(struct super_block *sb, void *data, int silent)
>  		[SMK_REVOKE_SUBJ] = {
>  			"revoke-subject", &smk_revoke_subj_ops,
>  			S_IRUGO|S_IWUSR},
> +		[SMK_CHANGE_RULE] = {
> +			"change-rule", &smk_change_rule_ops, S_IRUGO|S_IWUSR},
>  		/* last one */
>  			{""}
>  	};

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