audit: fix error handling in audit_data_to_entry()

Commit 219ca394 ("audit: use union for audit_field values since
they are mutually exclusive") combined a number of separate fields in
the audit_field struct into a single union.  Generally this worked
just fine because they are generally mutually exclusive.
Unfortunately in audit_data_to_entry() the overlap can be a problem
when a specific error case is triggered that causes the error path
code to attempt to cleanup an audit_field struct and the cleanup
involves attempting to free a stored LSM string (the lsm_str field).
Currently the code always has a non-NULL value in the
audit_field.lsm_str field as the top of the for-loop transfers a
value into audit_field.val (both .lsm_str and .val are part of the
same union); if audit_data_to_entry() fails and the audit_field
struct is specified to contain a LSM string, but the
audit_field.lsm_str has not yet been properly set, the error handling
code will attempt to free the bogus audit_field.lsm_str value that
was set with audit_field.val at the top of the for-loop.

This patch corrects this by ensuring that the audit_field.val is only
set when needed (it is cleared when the audit_field struct is
allocated with kcalloc()).  It also corrects a few other issues to
ensure that in case of error the proper error code is returned.

Cc: stable@vger.kernel.org
Fixes: 219ca394 ("audit: use union for audit_field values since they are mutually exclusive")
Reported-by: syzbot+1f4d90ead370d72e450b@syzkaller.appspotmail.com
Signed-off-by: Paul Moore <paul@paul-moore.com>

kernel/auditfilter.c

@@ -456,6 +456,7 @@ static struct audit_entry *audit_data_to_entry(struct audit_rule_data *data,
 	bufp = data->buf;
 	for (i = 0; i < data->field_count; i++) {
 		struct audit_field *f = &entry->rule.fields[i];
+		u32 f_val;
 
 		err = -EINVAL;
 
@@ -464,12 +465,12 @@ static struct audit_entry *audit_data_to_entry(struct audit_rule_data *data,
 			goto exit_free;
 
 		f->type = data->fields[i];
-		f->val = data->values[i];
+		f_val = data->values[i];
 
 		/* Support legacy tests for a valid loginuid */
-		if ((f->type == AUDIT_LOGINUID) && (f->val == AUDIT_UID_UNSET)) {
+		if ((f->type == AUDIT_LOGINUID) && (f_val == AUDIT_UID_UNSET)) {
 			f->type = AUDIT_LOGINUID_SET;
-			f->val = 0;
+			f_val = 0;
 			entry->rule.pflags |= AUDIT_LOGINUID_LEGACY;
 		}
 
@@ -485,7 +486,7 @@ static struct audit_entry *audit_data_to_entry(struct audit_rule_data *data,
 		case AUDIT_SUID:
 		case AUDIT_FSUID:
 		case AUDIT_OBJ_UID:
-			f->uid = make_kuid(current_user_ns(), f->val);
+			f->uid = make_kuid(current_user_ns(), f_val);
 			if (!uid_valid(f->uid))
 				goto exit_free;
 			break;
@@ -494,11 +495,12 @@ static struct audit_entry *audit_data_to_entry(struct audit_rule_data *data,
 		case AUDIT_SGID:
 		case AUDIT_FSGID:
 		case AUDIT_OBJ_GID:
-			f->gid = make_kgid(current_user_ns(), f->val);
+			f->gid = make_kgid(current_user_ns(), f_val);
 			if (!gid_valid(f->gid))
 				goto exit_free;
 			break;
 		case AUDIT_ARCH:
+			f->val = f_val;
 			entry->rule.arch_f = f;
 			break;
 		case AUDIT_SUBJ_USER:
@@ -511,11 +513,13 @@ static struct audit_entry *audit_data_to_entry(struct audit_rule_data *data,
 		case AUDIT_OBJ_TYPE:
 		case AUDIT_OBJ_LEV_LOW:
 		case AUDIT_OBJ_LEV_HIGH:
-			str = audit_unpack_string(&bufp, &remain, f->val);
-			if (IS_ERR(str))
+			str = audit_unpack_string(&bufp, &remain, f_val);
+			if (IS_ERR(str)) {
+				err = PTR_ERR(str);
 				goto exit_free;
-			entry->rule.buflen += f->val;
-
+			}
+			entry->rule.buflen += f_val;
+			f->lsm_str = str;
 			err = security_audit_rule_init(f->type, f->op, str,
 						       (void **)&f->lsm_rule);
 			/* Keep currently invalid fields around in case they
@@ -524,68 +528,71 @@ static struct audit_entry *audit_data_to_entry(struct audit_rule_data *data,
 				pr_warn("audit rule for LSM \'%s\' is invalid\n",
 					str);
 				err = 0;
-			}
-			if (err) {
-				kfree(str);
+			} else if (err)
 				goto exit_free;
-			} else
-				f->lsm_str = str;
 			break;
 		case AUDIT_WATCH:
-			str = audit_unpack_string(&bufp, &remain, f->val);
-			if (IS_ERR(str))
+			str = audit_unpack_string(&bufp, &remain, f_val);
+			if (IS_ERR(str)) {
+				err = PTR_ERR(str);
 				goto exit_free;
-			entry->rule.buflen += f->val;
-
-			err = audit_to_watch(&entry->rule, str, f->val, f->op);
+			}
+			err = audit_to_watch(&entry->rule, str, f_val, f->op);
 			if (err) {
 				kfree(str);
 				goto exit_free;
 			}
+			entry->rule.buflen += f_val;
 			break;
 		case AUDIT_DIR:
-			str = audit_unpack_string(&bufp, &remain, f->val);
-			if (IS_ERR(str))
+			str = audit_unpack_string(&bufp, &remain, f_val);
+			if (IS_ERR(str)) {
+				err = PTR_ERR(str);
 				goto exit_free;
-			entry->rule.buflen += f->val;
-
+			}
 			err = audit_make_tree(&entry->rule, str, f->op);
 			kfree(str);
 			if (err)
 				goto exit_free;
+			entry->rule.buflen += f_val;
 			break;
 		case AUDIT_INODE:
+			f->val = f_val;
 			err = audit_to_inode(&entry->rule, f);
 			if (err)
 				goto exit_free;
 			break;
 		case AUDIT_FILTERKEY:
-			if (entry->rule.filterkey || f->val > AUDIT_MAX_KEY_LEN)
+			if (entry->rule.filterkey || f_val > AUDIT_MAX_KEY_LEN)
 				goto exit_free;
-			str = audit_unpack_string(&bufp, &remain, f->val);
-			if (IS_ERR(str))
+			str = audit_unpack_string(&bufp, &remain, f_val);
+			if (IS_ERR(str)) {
+				err = PTR_ERR(str);
 				goto exit_free;
-			entry->rule.buflen += f->val;
+			}
+			entry->rule.buflen += f_val;
 			entry->rule.filterkey = str;
 			break;
 		case AUDIT_EXE:
-			if (entry->rule.exe || f->val > PATH_MAX)
+			if (entry->rule.exe || f_val > PATH_MAX)
 				goto exit_free;
-			str = audit_unpack_string(&bufp, &remain, f->val);
+			str = audit_unpack_string(&bufp, &remain, f_val);
 			if (IS_ERR(str)) {
 				err = PTR_ERR(str);
 				goto exit_free;
 			}
-			entry->rule.buflen += f->val;
-
-			audit_mark = audit_alloc_mark(&entry->rule, str, f->val);
+			audit_mark = audit_alloc_mark(&entry->rule, str, f_val);
 			if (IS_ERR(audit_mark)) {
 				kfree(str);
 				err = PTR_ERR(audit_mark);
 				goto exit_free;
 			}
+			entry->rule.buflen += f_val;
 			entry->rule.exe = audit_mark;
 			break;
+		default:
+			f->val = f_val;
+			break;
 		}
 	}