[PATCH v6 3/3] LSM: Add context interface for proc attrs

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

Subject: [PATCH v6 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>

---
 Documentation/security/LSM.txt |   8 +++
 fs/proc/base.c                 |   4 ++
 security/apparmor/lsm.c        |  35 +++++++++++--
 security/security.c            | 108 +++++++++++++++++++++++++++++++++++++++++
 security/selinux/hooks.c       |  20 +++++++-
 security/smack/smack_lsm.c     |  20 ++++----
 6 files changed, 180 insertions(+), 15 deletions(-)

diff --git a/Documentation/security/LSM.txt b/Documentation/security/LSM.txt
index 125c489..af3eb11 100644
--- a/Documentation/security/LSM.txt
+++ b/Documentation/security/LSM.txt
@@ -36,6 +36,14 @@ for SELinux would be in /proc/.../attr/selinux. Using the files
 found directly in /proc/.../attr (e.g. current) should be avoided.
 These files remain as legacy interfaces.
 
+The files named "context" in the attr directories contain the
+same information as the "current" files, but formatted to
+identify the module it comes from.
+
+if selinux is the active security module:
+	/proc/self/attr/context could contain selinux='unconfined_t'
+	/proc/self/attr/selinux/context could contain selinux='unconfined_t'
+
 Based on https://lkml.org/lkml/2007/10/26/215,
 a new LSM is accepted into the kernel when its intent (a description of
 what it tries to protect against and in what cases one would expect to
diff --git a/fs/proc/base.c b/fs/proc/base.c
index c6dbe81..923e4e2 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2565,6 +2565,7 @@ 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
@@ -2572,6 +2573,7 @@ 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
@@ -2581,6 +2583,7 @@ 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
@@ -2592,6 +2595,7 @@ 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 1d4843d..b865cf7 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -476,9 +476,13 @@ static int apparmor_getprocattr(struct task_struct *task, char *name,
 	const struct cred *cred = get_task_cred(task);
 	struct aa_task_cxt *cxt = cred_cxt(cred);
 	struct aa_profile *profile = NULL;
+	char *vp;
+	char *np;
 
 	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)
@@ -486,9 +490,29 @@ static int apparmor_getprocattr(struct task_struct *task, char *name,
 	else
 		error = -EINVAL;
 
-	if (profile)
-		error = aa_getprocattr(profile, value);
+	if (profile == NULL)
+		goto put_out;
+
+	error = aa_getprocattr(profile, &vp);
+	if (error < 0)
+		goto put_out;
+
+	if (strcmp(name, "context") == 0) {
+		*value = kasprintf(GFP_KERNEL, "apparmor='%s'", vp);
+		if (*value == NULL) {
+			error = -ENOMEM;
+			goto put_out;
+		}
+		np = strchr(*value, '\n');
+		if (np != NULL) {
+			np[0] = '\'';
+			np[1] = '\0';
+		}
+		error = strlen(*value);
+	} else
+		*value = vp;
 
+put_out:
 	aa_put_profile(profile);
 	put_cred(cred);
 
@@ -530,7 +554,7 @@ static int apparmor_setprocattr(struct task_struct *task, char *name,
 		goto out;
 
 	arg_size = size - (args - (largs ? largs : (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 +576,10 @@ 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
+		 */
 		goto fail;
 
 	if (!error)
diff --git a/security/security.c b/security/security.c
index 23d5868..656984a 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1207,8 +1207,47 @@ 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 = kasprintf(GFP_KERNEL, "%s,%s", *value, vp);
+				if (cp == NULL) {
+					kfree(*value);
+					kfree(vp);
+					return -ENOMEM;
+				}
+				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))
@@ -1225,7 +1264,76 @@ 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;
+
+	/*
+	 * If lsm is NULL look at all the modules to find one
+	 * that processes name. If lsm is not NULL only look at
+	 * that module.
+	 *
+	 * "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.
+		 * The kzalloc of size + 1 ensures a terminated string.
+		 */
+		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;
+			if (cp[0] == ',') {
+				if (cp == local)
+					goto free_out;
+				cp++;
+			}
+			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;
+			if (cp[0] == ',')
+				cp++;
+			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 0d039fc..cc7e95f 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -5795,6 +5795,8 @@ 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"))
@@ -5812,7 +5814,19 @@ 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 = kasprintf(GFP_KERNEL, "selinux='%s'", vp);
+			if (*value == NULL)
+				error = -ENOMEM;
+		}
+	}
+
 	if (error)
 		return error;
 	return len;
@@ -5852,6 +5866,8 @@ 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)
@@ -5911,7 +5927,7 @@ 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 7c12198..54627dd 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -3605,18 +3605,20 @@ static int smack_getprocattr(struct task_struct *p, char *name, char **value)
 {
 	struct smack_known *skp = smk_of_task_struct(p);
 	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) {
+		cp = kasprintf(GFP_KERNEL, "smack='%s'", skp->smk_known);
+		if (cp == NULL)
+			return -ENOMEM;
+	} 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);
 }
 
 /**
@@ -3653,7 +3655,7 @@ 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);
-- 
2.7.4