apparmor: ensure that undecidable profile attachments fail

commit 844b8292b6311ecd30ae63db1471edb26e01d895 upstream.

Profiles that have an undecidable overlap in their attachments are
being incorrectly handled. Instead of failing to attach the first one
encountered is being used.

eg.
  profile A /** { .. }
  profile B /*foo { .. }

have an unresolvable longest left attachment, they both have an exact
match on / and then have an overlapping expression that has no clear
winner.

Currently the winner will be the profile that is loaded first which
can result in non-deterministic behavior. Instead in this situation
the exec should fail.

Fixes: 898127c34ec0 ("AppArmor: functions for domain transitions")
Signed-off-by: John Johansen <john.johansen@canonical.com>
[bwh: Backported to 3.16:
 - Add 'info' parameter to x_to_profile(), done upstream in commit
   93c98a484c49 "apparmor: move exec domain mediation to using labels"
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

1 files changed, 37 insertions, 16 deletions

diff --git a/security/apparmor/domain.c b/security/apparmor/domain.c
index 24a21cd72b4c..4830e8ac3e85 100644
--- a/security/apparmor/domain.c
+++ b/security/apparmor/domain.c
@@ -126,6 +126,7 @@ static struct file_perms change_profile_perms(struct aa_profile *profile,
  * __attach_match_ - find an attachment match
  * @name - to match against  (NOT NULL)
  * @head - profile list to walk  (NOT NULL)
+ * @info - info message if there was an error (NOT NULL)
  *
  * Do a linear search on the profiles in the list.  There is a matching
  * preference where an exact match is preferred over a name which uses
@@ -137,28 +138,44 @@ static struct file_perms change_profile_perms(struct aa_profile *profile,
  * Returns: profile or NULL if no match found
  */
 static struct aa_profile *__attach_match(const char *name,
-					 struct list_head *head)
+					 struct list_head *head,
+					 const char **info)
 {
 	int len = 0;
+	bool conflict = false;
 	struct aa_profile *profile, *candidate = NULL;
 
 	list_for_each_entry_rcu(profile, head, base.list) {
 		if (profile->flags & PFLAG_NULL)
 			continue;
-		if (profile->xmatch && profile->xmatch_len > len) {
-			unsigned int state = aa_dfa_match(profile->xmatch,
-							  DFA_START, name);
-			u32 perm = dfa_user_allow(profile->xmatch, state);
-			/* any accepting state means a valid match. */
-			if (perm & MAY_EXEC) {
-				candidate = profile;
-				len = profile->xmatch_len;
+		if (profile->xmatch) {
+			if (profile->xmatch_len == len) {
+				conflict = true;
+				continue;
+			} else if (profile->xmatch_len > len) {
+				unsigned int state;
+				u32 perm;
+
+				state = aa_dfa_match(profile->xmatch,
+						     DFA_START, name);
+				perm = dfa_user_allow(profile->xmatch, state);
+				/* any accepting state means a valid match. */
+				if (perm & MAY_EXEC) {
+					candidate = profile;
+					len = profile->xmatch_len;
+					conflict = false;
+				}
 			}
 		} else if (!strcmp(profile->base.name, name))
 			/* exact non-re match, no more searching required */
 			return profile;
 	}
 
+	if (conflict) {
+		*info = "conflicting profile attachments";
+		return NULL;
+	}
+
 	return candidate;
 }
 
@@ -167,16 +184,18 @@ static struct aa_profile *__attach_match(const char *name,
  * @ns: the current namespace  (NOT NULL)
  * @list: list to search  (NOT NULL)
  * @name: the executable name to match against  (NOT NULL)
+ * @info: info message if there was an error
  *
  * Returns: profile or NULL if no match found
  */
 static struct aa_profile *find_attach(struct aa_namespace *ns,
-				      struct list_head *list, const char *name)
+				      struct list_head *list, const char *name,
+				      const char **info)
 {
 	struct aa_profile *profile;
 
 	rcu_read_lock();
-	profile = aa_get_profile(__attach_match(name, list));
+	profile = aa_get_profile(__attach_match(name, list, info));
 	rcu_read_unlock();
 
 	return profile;
@@ -298,7 +317,8 @@ static struct aa_profile *x_table_lookup(struct aa_profile *profile, u32 xindex)
  * Returns: refcounted profile or NULL if not found available
  */
 static struct aa_profile *x_to_profile(struct aa_profile *profile,
-				       const char *name, u32 xindex)
+				       const char *name, u32 xindex,
+				       const char **info)
 {
 	struct aa_profile *new_profile = NULL;
 	struct aa_namespace *ns = profile->ns;
@@ -312,11 +332,11 @@ static struct aa_profile *x_to_profile(struct aa_profile *profile,
 		if (xindex & AA_X_CHILD)
 			/* released by caller */
 			new_profile = find_attach(ns, &profile->base.profiles,
-						  name);
+						  name, info);
 		else
 			/* released by caller */
 			new_profile = find_attach(ns, &ns->base.profiles,
-						  name);
+						  name, info);
 		break;
 	case AA_X_TABLE:
 		/* released by caller */
@@ -385,7 +405,8 @@ int apparmor_bprm_set_creds(struct linux_binprm *bprm)
 			/* change_profile on exec already been granted */
 			new_profile = aa_get_profile(cxt->onexec);
 		else
-			new_profile = find_attach(ns, &ns->base.profiles, name);
+			new_profile = find_attach(ns, &ns->base.profiles, name,
+						  &info);
 		if (!new_profile)
 			goto cleanup;
 		/*
@@ -421,7 +442,7 @@ int apparmor_bprm_set_creds(struct linux_binprm *bprm)
 
 	if (perms.allow & MAY_EXEC) {
 		/* exec permission determine how to transition */
-		new_profile = x_to_profile(profile, name, perms.xindex);
+		new_profile = x_to_profile(profile, name, perms.xindex, &info);
 		if (!new_profile) {
 			if (perms.xindex & AA_X_INHERIT) {
 				/* (p|c|n)ix - don't change profile but do