[PATCH v3 3/3] LSM: Add context interface for proc attr

[Casey Schaufler <casey@schaufler-ca.com>]

Subject: [PATCH v3 3/3] LSM: Add context interface for proc attrs

The /proc/.../attr/current interface is used by all three
Linux security modules (SELinux, Smack and AppArmor) to
report and modify the process security attribute. This is
all fine when there is exactly one of these modules active
and the userspace code knows which it module it is.
It would require a major change to the "current" interface
to provide information about more than one set of process
security attributes. Instead, a "context" attribute is
added, which identifies the security module that the
information applies to. The format is:

	lsmname='context-value'

When multiple concurrent modules are supported the
/proc/.../attr/context interface will include the data
for all of the active modules.

	lsmname1='context-value1'lsmname2='context-value2'

The module specific subdirectories under attr contain context
entries that report the information for that specific module
in the same format.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>

---
 fs/proc/base.c             |  4 ++
 security/apparmor/lsm.c    | 34 ++++++++++++++--
 security/security.c        | 97 ++++++++++++++++++++++++++++++++++++++++++++++
 security/selinux/hooks.c   | 22 ++++++++++-
 security/smack/smack_lsm.c | 21 ++++++----
 5 files changed, 164 insertions(+), 14 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 182bc28..df94f26 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2532,6 +2532,7 @@ static const struct pid_entry selinux_attr_dir_stuff[] = {
 	ATTR("selinux", "fscreate",	S_IRUGO|S_IWUGO),
 	ATTR("selinux", "keycreate",	S_IRUGO|S_IWUGO),
 	ATTR("selinux", "sockcreate",	S_IRUGO|S_IWUGO),
+	ATTR("selinux", "context",	S_IRUGO|S_IWUGO),
 };
 LSM_DIR_OPS(selinux);
 #endif
@@ -2539,6 +2540,7 @@ LSM_DIR_OPS(selinux);
 #ifdef CONFIG_SECURITY_SMACK
 static const struct pid_entry smack_attr_dir_stuff[] = {
 	ATTR("smack", "current",	S_IRUGO|S_IWUGO),
+	ATTR("smack", "context",	S_IRUGO|S_IWUGO),
 };
 LSM_DIR_OPS(smack);
 #endif
@@ -2548,6 +2550,7 @@ static const struct pid_entry apparmor_attr_dir_stuff[] = {
 	ATTR("apparmor", "current",	S_IRUGO|S_IWUGO),
 	ATTR("apparmor", "prev",	S_IRUGO),
 	ATTR("apparmor", "exec",	S_IRUGO|S_IWUGO),
+	ATTR("apparmor", "context",	S_IRUGO|S_IWUGO),
 };
 LSM_DIR_OPS(apparmor);
 #endif
@@ -2559,6 +2562,7 @@ static const struct pid_entry attr_dir_stuff[] = {
 	ATTR(NULL, "fscreate",		S_IRUGO|S_IWUGO),
 	ATTR(NULL, "keycreate",		S_IRUGO|S_IWUGO),
 	ATTR(NULL, "sockcreate",	S_IRUGO|S_IWUGO),
+	ATTR(NULL, "context",		S_IRUGO|S_IWUGO),
 #ifdef CONFIG_SECURITY_SELINUX
 	DIR("selinux",			S_IRUGO|S_IXUGO,
 	    proc_selinux_attr_dir_inode_ops, proc_selinux_attr_dir_ops),
diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index fb0fb03..3790a7d 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -479,6 +479,8 @@ static int apparmor_getprocattr(struct task_struct *task, char *name,
 
 	if (strcmp(name, "current") == 0)
 		profile = aa_get_newest_profile(cxt->profile);
+	else if (strcmp(name, "context") == 0)
+		profile = aa_get_newest_profile(cxt->profile);
 	else if (strcmp(name, "prev") == 0  && cxt->previous)
 		profile = aa_get_newest_profile(cxt->previous);
 	else if (strcmp(name, "exec") == 0 && cxt->onexec)
@@ -486,8 +488,29 @@ static int apparmor_getprocattr(struct task_struct *task, char *name,
 	else
 		error = -EINVAL;
 
-	if (profile)
-		error = aa_getprocattr(profile, value);
+	if (profile) {
+		if (strcmp(name, "context") == 0) {
+			char *vp;
+			char *np;
+
+			error = aa_getprocattr(profile, &vp);
+			if (error > 0) {
+				error += 12;
+				*value = kzalloc(error, GFP_KERNEL);
+				if (*value == NULL)
+					error = -ENOMEM;
+				else {
+					sprintf(*value, "apparmor='%s'", vp);
+					np = strchr(*value, '\n');
+					if (np != NULL) {
+						np[0] = '\'';
+						np[1] = '\0';
+					}
+				}
+			}
+		} else
+			error = aa_getprocattr(profile, value);
+	}
 
 	aa_put_profile(profile);
 	put_cred(cred);
@@ -530,7 +553,7 @@ static int apparmor_setprocattr(struct task_struct *task, char *name,
 		return -EINVAL;
 
 	arg_size = size - (args - (char *) value);
-	if (strcmp(name, "current") == 0) {
+	if (strcmp(name, "current") == 0 || strcmp(name, "context") == 0) {
 		if (strcmp(command, "changehat") == 0) {
 			error = aa_setprocattr_changehat(args, arg_size,
 							 !AA_DO_TEST);
@@ -552,7 +575,10 @@ static int apparmor_setprocattr(struct task_struct *task, char *name,
 		else
 			goto fail;
 	} else
-		/* only support the "current" and "exec" process attributes */
+		/*
+		 * only support the "current", context and "exec"
+		 * process attributes
+		 */
 		return -EINVAL;
 
 	if (!error)
diff --git a/security/security.c b/security/security.c
index 41ac80d..6f7ad19 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1187,8 +1187,49 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name,
 				char **value)
 {
 	struct security_hook_list *hp;
+	char *vp;
+	char *cp = NULL;
 	int rc = -EINVAL;
+	int trc;
 
+	/*
+	 * "context" requires work here in addition to what
+	 * the modules provide.
+	 */
+	if (strcmp(name, "context") == 0) {
+		*value = NULL;
+		list_for_each_entry(hp,
+				&security_hook_heads.getprocattr, list) {
+			if (lsm != NULL && strcmp(lsm, hp->lsm))
+				continue;
+			trc = hp->hook.getprocattr(p, "context", &vp);
+			if (trc == -ENOENT)
+				continue;
+			if (trc <= 0) {
+				kfree(*value);
+				return trc;
+			}
+			rc = trc;
+			if (*value == NULL) {
+				*value = vp;
+			} else {
+				cp = kzalloc(strlen(*value) + strlen(vp) + 1,
+					GFP_KERNEL);
+				if (cp == NULL) {
+					kfree(*value);
+					kfree(vp);
+					return -ENOMEM;
+				}
+				sprintf(cp, "%s%s", *value, vp);
+				kfree(*value);
+				kfree(vp);
+				*value = cp;
+			}
+		}
+		if (rc > 0)
+			return strlen(*value);
+		return rc;
+	}
 
 	list_for_each_entry(hp, &security_hook_heads.getprocattr, list) {
 		if (lsm != NULL && strcmp(lsm, hp->lsm))
@@ -1205,7 +1246,63 @@ int security_setprocattr(struct task_struct *p, const char *lsm, char *name,
 {
 	struct security_hook_list *hp;
 	int rc = -EINVAL;
+	char *local;
+	char *cp;
+	int slen;
+	int failed = 0;
 
+	/*
+	 * "context" is handled directly here.
+	 */
+	if (strcmp(name, "context") == 0) {
+		/*
+		 * First verify that the input is acceptable.
+		 * lsm1='v1'lsm2='v2'lsm3='v3'
+		 *
+		 * A note on the use of strncmp() below.
+		 * The check is for the substring at the beginning of cp.
+		 */
+		local = kzalloc(size + 1, GFP_KERNEL);
+		memcpy(local, value, size);
+		cp = local;
+		list_for_each_entry(hp, &security_hook_heads.setprocattr,
+					list) {
+			if (lsm != NULL && strcmp(lsm, hp->lsm))
+				continue;
+			slen = strlen(hp->lsm);
+			if (strncmp(cp, hp->lsm, slen))
+				goto free_out;
+			cp += slen;
+			if (cp[0] != '=' || cp[1] != '\'' || cp[2] == '\'')
+				goto free_out;
+			for (cp += 2; cp[0] != '\''; cp++)
+				if (cp[0] == '\0')
+					goto free_out;
+			cp++;
+		}
+		cp = local;
+		list_for_each_entry(hp, &security_hook_heads.setprocattr,
+					list) {
+			if (lsm != NULL && strcmp(lsm, hp->lsm))
+				continue;
+			cp += strlen(hp->lsm) + 2;
+			for (slen = 0; cp[slen] != '\''; slen++)
+				;
+			cp[slen] = '\0';
+
+			rc = hp->hook.setprocattr(p, "context", cp, slen);
+			if (rc < 0)
+				failed = rc;
+			cp += slen + 1;
+		}
+		if (failed != 0)
+			rc = failed;
+		else
+			rc = size;
+free_out:
+		kfree(local);
+		return rc;
+	}
 	list_for_each_entry(hp, &security_hook_heads.setprocattr, list) {
 		if (lsm != NULL && strcmp(lsm, hp->lsm))
 			continue;
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index ed3a757..3a21c2b 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -5711,6 +5711,8 @@ static int selinux_getprocattr(struct task_struct *p,
 
 	if (!strcmp(name, "current"))
 		sid = __tsec->sid;
+	else if (!strcmp(name, "context"))
+		sid = __tsec->sid;
 	else if (!strcmp(name, "prev"))
 		sid = __tsec->osid;
 	else if (!strcmp(name, "exec"))
@@ -5728,7 +5730,21 @@ static int selinux_getprocattr(struct task_struct *p,
 	if (!sid)
 		return 0;
 
-	error = security_sid_to_context(sid, value, &len);
+	if (strcmp(name, "context")) {
+		error = security_sid_to_context(sid, value, &len);
+	} else {
+		char *vp;
+
+		error = security_sid_to_context(sid, &vp, &len);
+		if (!error) {
+			*value = kzalloc(len + 10, GFP_KERNEL);
+			if (*value == NULL)
+				error = -ENOMEM;
+			else
+				sprintf(*value, "selinux='%s'", vp);
+		}
+	}
+
 	if (error)
 		return error;
 	return len;
@@ -5768,6 +5784,8 @@ static int selinux_setprocattr(struct task_struct *p,
 		error = current_has_perm(p, PROCESS__SETSOCKCREATE);
 	else if (!strcmp(name, "current"))
 		error = current_has_perm(p, PROCESS__SETCURRENT);
+	else if (!strcmp(name, "context"))
+		error = current_has_perm(p, PROCESS__SETCURRENT);
 	else
 		error = -EINVAL;
 	if (error)
@@ -5827,7 +5845,7 @@ static int selinux_setprocattr(struct task_struct *p,
 		tsec->keycreate_sid = sid;
 	} else if (!strcmp(name, "sockcreate")) {
 		tsec->sockcreate_sid = sid;
-	} else if (!strcmp(name, "current")) {
+	} else if (!strcmp(name, "current") || !strcmp(name, "context")) {
 		error = -EINVAL;
 		if (sid == 0)
 			goto abort_change;
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 3577009..d2d8624 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -3576,16 +3576,21 @@ static int smack_getprocattr(struct task_struct *p, char *name, char **value)
 	char *cp;
 	int slen;
 
-	if (strcmp(name, "current") != 0)
+	if (strcmp(name, "current") == 0) {
+		cp = kstrdup(skp->smk_known, GFP_KERNEL);
+		if (cp == NULL)
+			return -ENOMEM;
+	} else if (strcmp(name, "context") == 0) {
+		slen = strlen(skp->smk_known) + 9;
+		cp = kzalloc(slen, GFP_KERNEL);
+		if (cp == NULL)
+			return -ENOMEM;
+		sprintf(cp, "smack='%s'", skp->smk_known);
+	} else
 		return -EINVAL;
 
-	cp = kstrdup(skp->smk_known, GFP_KERNEL);
-	if (cp == NULL)
-		return -ENOMEM;
-
-	slen = strlen(cp);
 	*value = cp;
-	return slen;
+	return strlen(cp);
 }
 
 /**
@@ -3622,7 +3627,7 @@ static int smack_setprocattr(struct task_struct *p, char *name,
 	if (value == NULL || size == 0 || size >= SMK_LONGLABEL)
 		return -EINVAL;
 
-	if (strcmp(name, "current") != 0)
+	if (strcmp(name, "current") != 0 && strcmp(name, "context") != 0)
 		return -EINVAL;
 
 	skp = smk_import_entry(value, size);