Unmount USB on start (#1211)

* WIP Allow configuring Santa to unmount existing mass storage devices on startup

* WIP fixup existing tests

* Add unmount on startup tests

Source/common/SNTCommonEnums.h

@@ -158,6 +158,12 @@ typedef NS_ENUM(NSInteger, SNTOverrideFileAccessAction) {
   SNTOverrideFileAccessActionDiable,
 };
 
+typedef NS_ENUM(NSInteger, SNTDeviceManagerStartupPreferences) {
+  SNTDeviceManagerStartupPreferencesNone,
+  SNTDeviceManagerStartupPreferencesUnmount,
+  SNTDeviceManagerStartupPreferencesForceUnmount,
+};
+
 #ifdef __cplusplus
 enum class FileAccessPolicyDecision {
   kNoPolicy,

Source/common/SNTConfigurator.h

@@ -454,6 +454,20 @@
 ///
 @property(nonatomic) NSArray<NSString *> *remountUSBMode;
 
+///
+/// If set, defines the action that should be taken on existing USB mounts when
+/// Santa starts up.
+///
+/// Supported values are:
+///   * "Unmount": Unmount mass storage devices
+///   * "ForceUnmount": Force unmount mass storage devices
+///
+///
+/// Note: Existing mounts with mount flags that are a superset of RemountUSBMode
+/// are unaffected and left mounted.
+///
+@property(readonly, nonatomic) SNTDeviceManagerStartupPreferences onStartUSBOptions;
+
 ///
 /// If set, will override the action taken when a file access rule violation
 /// occurs. This setting will apply across all rules in the file access policy.

Source/common/SNTConfigurator.m

@@ -121,6 +121,7 @@ @implementation SNTConfigurator
 static NSString *const kFailClosedKey = @"FailClosed";
 static NSString *const kBlockUSBMountKey = @"BlockUSBMount";
 static NSString *const kRemountUSBModeKey = @"RemountUSBMode";
+static NSString *const kOnStartUSBOptions = @"OnStartUSBOptions";
 static NSString *const kEnableTransitiveRulesKey = @"EnableTransitiveRules";
 static NSString *const kEnableTransitiveRulesKeyDeprecated = @"EnableTransitiveWhitelisting";
 static NSString *const kAllowedPathRegexKey = @"AllowedPathRegex";
@@ -181,6 +182,7 @@ - (instancetype)init {
       kBlockedPathRegexKeyDeprecated : re,
       kBlockUSBMountKey : number,
       kRemountUSBModeKey : array,
+      kOnStartUSBOptions : string,
       kEnablePageZeroProtectionKey : number,
       kEnableBadSignatureProtectionKey : number,
       kEnableSilentModeKey : number,
@@ -635,6 +637,18 @@ - (void)setRemountUSBMode:(NSArray<NSString *> *)args {
   return args;
 }
 
+- (SNTDeviceManagerStartupPreferences)onStartUSBOptions {
+  NSString *action = [self.configState[kOnStartUSBOptions] lowercaseString];
+
+  if ([action isEqualToString:@"unmount"]) {
+    return SNTDeviceManagerStartupPreferencesUnmount;
+  } else if ([action isEqualToString:@"forceunmount"]) {
+    return SNTDeviceManagerStartupPreferencesForceUnmount;
+  } else {
+    return SNTDeviceManagerStartupPreferencesNone;
+  }
+}
+
 - (NSDictionary<NSString *, SNTRule *> *)staticRules {
   return self.cachedStaticRules;
 }

Source/santad/BUILD

@@ -395,6 +395,7 @@ objc_library(
         ":Metrics",
         ":SNTEndpointSecurityClient",
         ":SNTEndpointSecurityEventHandler",
+        "//Source/common:SNTCommonEnums",
         "//Source/common:SNTDeviceEvent",
         "//Source/common:SNTLogging",
     ],
@@ -1317,6 +1318,7 @@ santa_unit_test(
         ":Metrics",
         ":MockEndpointSecurityAPI",
         ":SNTEndpointSecurityDeviceManager",
+        "//Source/common:SNTCommonEnums",
         "//Source/common:SNTConfigurator",
         "//Source/common:SNTDeviceEvent",
         "//Source/common:TestUtils",

Source/santad/EventProviders/DiskArbitrationTestUtil.h

@@ -16,6 +16,9 @@
 #include <CoreFoundation/CoreFoundation.h>
 #include <DiskArbitration/DiskArbitration.h>
 #include <Foundation/Foundation.h>
+#include <sys/mount.h>
+#include <sys/param.h>
+#include <sys/ucred.h>
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -27,6 +30,7 @@ NS_ASSUME_NONNULL_BEGIN
 @interface MockDADisk : NSObject
 @property(nonatomic) NSDictionary *diskDescription;
 @property(nonatomic, readwrite) NSString *name;
+@property(nonatomic) BOOL wasUnmounted;
 @end
 
 typedef void (^MockDADiskAppearedCallback)(DADiskRef ref);
@@ -49,6 +53,23 @@ typedef void (^MockDADiskAppearedCallback)(DADiskRef ref);
 + (instancetype _Nonnull)mockDiskArbitration;
 @end
 
+@interface MockStatfs : NSObject
+@property NSString *fromName;
+@property NSString *onName;
+@property NSNumber *flags;
+
+- (instancetype _Nonnull)initFrom:(NSString *)from on:(NSString *)on flags:(NSNumber *)flags;
+@end
+
+@interface MockMounts : NSObject
+@property(nonatomic) NSMutableDictionary<NSString *, MockStatfs *> *mounts;
+
+- (instancetype _Nonnull)init;
+- (void)reset;
+- (void)insert:(MockStatfs *)sfs;
++ (instancetype _Nonnull)mockMounts;
+@end
+
 //
 // All DiskArbitration functions used in SNTEndpointSecurityDeviceManager
 // and shimmed out accordingly.
@@ -81,5 +102,9 @@ void DARegisterDiskDescriptionChangedCallback(DASessionRef session,
 void DASessionSetDispatchQueue(DASessionRef session, dispatch_queue_t __nullable queue);
 DASessionRef __nullable DASessionCreate(CFAllocatorRef __nullable allocator);
 
+void DADiskUnmount(DADiskRef disk, DADiskUnmountOptions options,
+                   DADiskUnmountCallback __nullable callback, void *__nullable context);
+int getmntinfo_r_np(struct statfs *__nullable *__nullable mntbufp, int flags);
+
 CF_EXTERN_C_END
 NS_ASSUME_NONNULL_END

Source/santad/EventProviders/DiskArbitrationTestUtil.mm

@@ -14,6 +14,9 @@
 #import <Foundation/Foundation.h>
 
 #include <stdlib.h>
+#include <sys/mount.h>
+#include <sys/param.h>
+#include <sys/ucred.h>
 
 #import "Source/santad/EventProviders/DiskArbitrationTestUtil.h"
 
@@ -62,6 +65,47 @@ + (instancetype _Nonnull)mockDiskArbitration {
 
 @end
 
+@implementation MockStatfs
+- (instancetype _Nonnull)initFrom:(NSString *)from on:(NSString *)on flags:(NSNumber *)flags {
+  self = [super init];
+  if (self) {
+    _fromName = from;
+    _onName = on;
+    _flags = flags;
+  }
+  return self;
+}
+@end
+
+@implementation MockMounts
+
+- (instancetype _Nonnull)init {
+  self = [super init];
+  if (self) {
+    _mounts = [NSMutableDictionary dictionary];
+  }
+  return self;
+}
+
+- (void)reset {
+  [self.mounts removeAllObjects];
+}
+
+- (void)insert:(MockStatfs *)sfs {
+  self.mounts[sfs.fromName] = sfs;
+}
+
++ (instancetype _Nonnull)mockMounts {
+  static MockMounts *sharedMounts;
+  static dispatch_once_t onceToken;
+  dispatch_once(&onceToken, ^{
+    sharedMounts = [[MockMounts alloc] init];
+  });
+  return sharedMounts;
+}
+
+@end
+
 void DADiskMountWithArguments(DADiskRef _Nonnull disk, CFURLRef __nullable path,
                               DADiskMountOptions options, DADiskMountCallback __nullable callback,
                               void *__nullable context,
@@ -117,4 +161,32 @@ DASessionRef __nullable DASessionCreate(CFAllocatorRef __nullable allocator) {
   return (__bridge DASessionRef)[MockDiskArbitration mockDiskArbitration];
 };
 
+void DADiskUnmount(DADiskRef disk, DADiskUnmountOptions options,
+                   DADiskUnmountCallback __nullable callback, void *__nullable context) {
+  MockDADisk *mockDisk = (__bridge MockDADisk *)disk;
+  mockDisk.wasUnmounted = YES;
+
+  dispatch_semaphore_t sema = (__bridge dispatch_semaphore_t)context;
+  dispatch_semaphore_signal(sema);
+}
+
+int getmntinfo_r_np(struct statfs *__nullable *__nullable mntbufp, int flags) {
+  MockMounts *mockMounts = [MockMounts mockMounts];
+
+  struct statfs *sfs = (struct statfs *)calloc(mockMounts.mounts.count, sizeof(struct statfs));
+
+  __block NSUInteger i = 0;
+  [mockMounts.mounts
+    enumerateKeysAndObjectsUsingBlock:^(NSString *key, MockStatfs *mockSfs, BOOL *stop) {
+      strlcpy(sfs[i].f_mntfromname, mockSfs.fromName.UTF8String, sizeof(sfs[i].f_mntfromname));
+      strlcpy(sfs[i].f_mntonname, mockSfs.onName.UTF8String, sizeof(sfs[i].f_mntonname));
+      sfs[i].f_flags = [mockSfs.flags unsignedIntValue];
+      i++;
+    }];
+
+  *mntbufp = sfs;
+
+  return (int)mockMounts.mounts.count;
+}
+
 NS_ASSUME_NONNULL_END

Source/santad/EventProviders/SNTEndpointSecurityDeviceManager.h

@@ -15,6 +15,7 @@
 #include <DiskArbitration/DiskArbitration.h>
 #import <Foundation/Foundation.h>
 
+#import "Source/common/SNTCommonEnums.h"
 #import "Source/common/SNTDeviceEvent.h"
 #import "Source/santad/EventProviders/AuthResultCache.h"
 #include "Source/santad/EventProviders/EndpointSecurity/EndpointSecurityAPI.h"
@@ -39,11 +40,16 @@ typedef void (^SNTDeviceBlockCallback)(SNTDeviceEvent *event);
 @property(nonatomic, nullable) SNTDeviceBlockCallback deviceBlockCallback;
 
 - (instancetype)
-    initWithESAPI:
-      (std::shared_ptr<santa::santad::event_providers::endpoint_security::EndpointSecurityAPI>)esApi
-          metrics:(std::shared_ptr<santa::santad::Metrics>)metrics
-           logger:(std::shared_ptr<santa::santad::logs::endpoint_security::Logger>)logger
-  authResultCache:(std::shared_ptr<santa::santad::event_providers::AuthResultCache>)authResultCache;
+       initWithESAPI:
+         (std::shared_ptr<santa::santad::event_providers::endpoint_security::EndpointSecurityAPI>)
+           esApi
+             metrics:(std::shared_ptr<santa::santad::Metrics>)metrics
+              logger:(std::shared_ptr<santa::santad::logs::endpoint_security::Logger>)logger
+     authResultCache:
+       (std::shared_ptr<santa::santad::event_providers::AuthResultCache>)authResultCache
+       blockUSBMount:(BOOL)blockUSBMount
+      remountUSBMode:(nullable NSArray<NSString *> *)remountUSBMode
+  startupPreferences:(SNTDeviceManagerStartupPreferences)startupPrefs;
 
 @end