apparmor: rework and cleanup fperm computation

shorten the name of some of the mapping functions which shortens line
lengths.

change the mapping so it returns the perm table instead of operating
directly on the file struct.

Handle potential memory allocation failure.
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/policy_unpack.c

@@ -697,8 +697,7 @@ static u32 map_old_perms(u32 old)
 	return new;
 }
 
-static void __aa_compute_fperms_allow(struct aa_perms *perms,
-				      struct aa_dfa *dfa,
+static void compute_fperms_allow(struct aa_perms *perms, struct aa_dfa *dfa,
 				 unsigned int state)
 {
 	perms->allow |= AA_MAY_GETATTR;
@@ -710,7 +709,7 @@ static void __aa_compute_fperms_allow(struct aa_perms *perms,
 		perms->allow |= AA_MAY_ONEXEC;
 }
 
-static struct aa_perms __aa_compute_fperms_user(struct aa_dfa *dfa,
+static struct aa_perms compute_fperms_user(struct aa_dfa *dfa,
 					   unsigned int state)
 {
 	struct aa_perms perms = { };
@@ -720,12 +719,12 @@ static struct aa_perms __aa_compute_fperms_user(struct aa_dfa *dfa,
 	perms.quiet = map_old_perms(dfa_user_quiet(dfa, state));
 	perms.xindex = dfa_user_xindex(dfa, state);
 
-	__aa_compute_fperms_allow(&perms, dfa, state);
+	compute_fperms_allow(&perms, dfa, state);
 
 	return perms;
 }
 
-static struct aa_perms __aa_compute_fperms_other(struct aa_dfa *dfa,
+static struct aa_perms compute_fperms_other(struct aa_dfa *dfa,
 					    unsigned int state)
 {
 	struct aa_perms perms = { };
@@ -735,7 +734,7 @@ static struct aa_perms __aa_compute_fperms_other(struct aa_dfa *dfa,
 	perms.quiet = map_old_perms(dfa_other_quiet(dfa, state));
 	perms.xindex = dfa_other_xindex(dfa, state);
 
-	__aa_compute_fperms_allow(&perms, dfa, state);
+	compute_fperms_allow(&perms, dfa, state);
 
 	return perms;
 }
@@ -743,41 +742,46 @@ static struct aa_perms __aa_compute_fperms_other(struct aa_dfa *dfa,
 /**
  * aa_compute_fperms - convert dfa compressed perms to internal perms and store
  *		       them so they can be retrieved later.
- * @file_rules: a file_rules structure containing a dfa (NOT NULL) for which
- *		permissions will be computed   (NOT NULL)
+ * @dfa: a dfa using fperms to remap to internal permissions
  *
- * TODO: convert from dfa + state to permission entry
+ * Returns: remapped perm table
  */
-static void aa_compute_fperms(struct aa_file_rules *file_rules)
+static struct aa_perms *compute_fperms(struct aa_dfa *dfa)
 {
 	int state;
-	int state_count = file_rules->dfa->tables[YYTD_ID_BASE]->td_lolen;
+	int state_count;
+	struct aa_perms *table;
 
-	// DFAs are restricted from having a state_count of less than 2
-	file_rules->fperms_table = kvzalloc(
-			state_count * 2 * sizeof(struct aa_perms), GFP_KERNEL);
+	AA_BUG(!dfa);
 
-	// Since fperms_table is initialized with zeroes via kvzalloc(), we can
-	// skip the trap state (state == 0)
+	state_count = dfa->tables[YYTD_ID_BASE]->td_lolen;
+	/* DFAs are restricted from having a state_count of less than 2 */
+	table = kvzalloc(state_count * 2 * sizeof(struct aa_perms), GFP_KERNEL);
+	if (!table)
+		return NULL;
+
+	/* zero init so skip the trap state (state == 0) */
 	for (state = 1; state < state_count; state++) {
-		file_rules->fperms_table[state * 2] =
-			__aa_compute_fperms_user(file_rules->dfa, state);
-		file_rules->fperms_table[state * 2 + 1] =
-			__aa_compute_fperms_other(file_rules->dfa, state);
+		table[state * 2] = compute_fperms_user(dfa, state);
+		table[state * 2 + 1] = compute_fperms_other(dfa, state);
 	}
+
+	return table;
 }
 
-static u32 *aa_compute_xmatch_perms(struct aa_dfa *xmatch)
+static u32 *compute_xmatch_perms(struct aa_dfa *xmatch)
 {
 	u32 *perms_table;
 	int state;
-	int state_count = xmatch->tables[YYTD_ID_BASE]->td_lolen;
+	int state_count;
+
+	AA_BUG(!xmatch);
 
-	// DFAs are restricted from having a state_count of less than 2
+	state_count = xmatch->tables[YYTD_ID_BASE]->td_lolen;
+	/* DFAs are restricted from having a state_count of less than 2 */
 	perms_table = kvcalloc(state_count, sizeof(u32), GFP_KERNEL);
 
-	// Since perms_table is initialized with zeroes via kvcalloc(), we can
-	// skip the trap state (state == 0)
+	/* zero init so skip the trap state (state == 0) */
 	for (state = 1; state < state_count; state++)
 		perms_table[state] = dfa_user_allow(xmatch, state);
 
@@ -850,8 +854,7 @@ static struct aa_profile *unpack_profile(struct aa_ext *e, char **ns_name)
 		}
 		profile->xmatch_len = tmp;
 
-		profile->xmatch_perms = aa_compute_xmatch_perms(
-			profile->xmatch);
+		profile->xmatch_perms = compute_xmatch_perms(profile->xmatch);
 	}
 
 	/* disconnected attachment string is optional */
@@ -997,8 +1000,11 @@ static struct aa_profile *unpack_profile(struct aa_ext *e, char **ns_name)
 	} else
 		profile->file.dfa = aa_get_dfa(nulldfa);
 
-	aa_compute_fperms(&(profile->file));
-
+	profile->file.fperms_table = compute_fperms(profile->file.dfa);
+	if (!profile->file.fperms_table) {
+		info = "failed to remap file permission table";
+		goto fail;
+	}
 	if (!unpack_trans_table(e, profile)) {
 		info = "failed to unpack profile transition table";
 		goto fail;