Validate hosts block contents during integrity checks

Block Management/HostFileBlocker.h

@@ -42,6 +42,7 @@
 - (void)appendExistingBlockWithRuleForDomain:(NSString*)domainName;
 
 - (BOOL)containsSelfControlBlock;
+- (BOOL)containsExpectedRulesForBlocklist:(NSArray<NSString*>*)blocklist;
 
 - (void)removeSelfControlBlock;
 

Block Management/HostFileBlocker.m

@@ -21,6 +21,8 @@
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #import "HostFileBlocker.h"
+#import "SCBlockEntry.h"
+#import "NSString+IPAddress.h"
 
 NSString* const kHostFileBlockerPath = @"/etc/hosts";
 NSString* const kHostFileBlockerSelfControlHeader = @"# BEGIN SELFCONTROL BLOCK";
@@ -182,6 +184,74 @@ - (BOOL)containsSelfControlBlock {
 	return ret;
 }
 
+- (NSSet<NSString*>*)selfControlBlockRuleSet {
+    NSMutableSet<NSString*>* ruleSet = [NSMutableSet set];
+
+    NSRange startRange = [newFileContents rangeOfString: kHostFileBlockerSelfControlHeader];
+    NSRange endRange = [newFileContents rangeOfString: kHostFileBlockerSelfControlFooter];
+    if (startRange.location == NSNotFound || endRange.location == NSNotFound || endRange.location <= startRange.location) {
+        return ruleSet;
+    }
+
+    NSUInteger blockStart = startRange.location + startRange.length;
+    NSRange blockRange = NSMakeRange(blockStart, endRange.location - blockStart);
+    NSString* blockContents = [newFileContents substringWithRange: blockRange];
+    NSArray<NSString*>* lines = [blockContents componentsSeparatedByCharactersInSet: [NSCharacterSet newlineCharacterSet]];
+    NSCharacterSet* whitespace = [NSCharacterSet whitespaceAndNewlineCharacterSet];
+
+    for (NSString* line in lines) {
+        NSString* trimmedLine = [line stringByTrimmingCharactersInSet: whitespace];
+        if (trimmedLine.length == 0 || [trimmedLine hasPrefix: @"#"]) {
+            continue;
+        }
+
+        NSArray<NSString*>* parts = [trimmedLine componentsSeparatedByCharactersInSet: whitespace];
+        NSMutableArray<NSString*>* nonEmptyParts = [NSMutableArray array];
+        for (NSString* part in parts) {
+            if (part.length > 0) {
+                [nonEmptyParts addObject: part];
+            }
+        }
+        if (nonEmptyParts.count < 2) {
+            continue;
+        }
+
+        NSString* address = nonEmptyParts[0];
+        for (NSUInteger i = 1; i < nonEmptyParts.count; i++) {
+            [ruleSet addObject: [NSString stringWithFormat: @"%@ %@", address, nonEmptyParts[i]]];
+        }
+    }
+
+    return ruleSet;
+}
+
+- (BOOL)containsExpectedRulesForBlocklist:(NSArray<NSString*>*)blocklist {
+    [strLock lock];
+
+    BOOL ret = ([newFileContents rangeOfString: kHostFileBlockerSelfControlHeader].location != NSNotFound);
+    if (ret) {
+        NSSet<NSString*>* blockRuleSet = [self selfControlBlockRuleSet];
+
+        for (NSString* blocklistString in blocklist) {
+            SCBlockEntry* entry = [SCBlockEntry entryFromString: blocklistString];
+            if (entry == nil || entry.port || [entry.hostname rangeOfString: @"*"].location != NSNotFound || [entry.hostname isValidIPAddress]) {
+                continue;
+            }
+
+            NSString* ipv4Rule = [NSString stringWithFormat: @"0.0.0.0 %@", entry.hostname];
+            NSString* ipv6Rule = [NSString stringWithFormat: @":: %@", entry.hostname];
+            if (![blockRuleSet containsObject: ipv4Rule] || ![blockRuleSet containsObject: ipv6Rule]) {
+                NSLog(@"INFO: SelfControl hosts block is missing expected rule(s) for %@", entry.hostname);
+                ret = NO;
+                break;
+            }
+        }
+    }
+
+    [strLock unlock];
+    return ret;
+}
+
 - (void)removeSelfControlBlock {
 	if(![self containsSelfControlBlock])
 		return;

Block Management/HostFileBlockerSet.m

@@ -112,6 +112,14 @@ - (BOOL)containsSelfControlBlock {
     return ret;
 }
 
+- (BOOL)containsExpectedRulesForBlocklist:(NSArray<NSString*>*)blocklist {
+    BOOL ret = YES;
+    for (HostFileBlocker* blocker in self.blockers) {
+        ret = ret && [blocker containsExpectedRulesForBlocklist: blocklist];
+    }
+    return ret;
+}
+
 - (void)removeSelfControlBlock {
     for (HostFileBlocker* blocker in self.blockers) {
         [blocker removeSelfControlBlock];

Common/SCSettings.m

@@ -271,10 +271,10 @@ - (void)writeSettingsWithCompletion:(nullable void(^)(NSError* _Nullable))comple
             NSError* chmodErr;
             BOOL chmodSuccessful = [[NSFileManager defaultManager]
                                     setAttributes: @{
-                                        NSFileOwnerAccountID: [NSNumber numberWithUnsignedLong: 0],
-                                        NSFileGroupOwnerAccountID: [NSNumber numberWithUnsignedLong: 0],
-                                        NSFilePosixPermissions: [NSNumber numberWithShort: 0755]
-                                    }
+	                                        NSFileOwnerAccountID: [NSNumber numberWithUnsignedLong: 0],
+	                                        NSFileGroupOwnerAccountID: [NSNumber numberWithUnsignedLong: 0],
+	                                        NSFilePosixPermissions: [NSNumber numberWithShort: 0644]
+	                                    }
                                     ofItemAtPath: SCSettings.securedSettingsFilePath
                                     error: &chmodErr];
 

Daemon/SCDaemonBlockMethods.m

@@ -349,7 +349,8 @@ + (void)checkBlockIntegrity {
     SCSettings* settings = [SCSettings sharedSettings];
     PacketFilter* pf = [[PacketFilter alloc] init];
     HostFileBlockerSet* hostFileBlockerSet = [[HostFileBlockerSet alloc] init];
-    if(![pf containsSelfControlBlock] || (![settings boolForKey: @"ActiveBlockAsWhitelist"] && ![hostFileBlockerSet.defaultBlocker containsSelfControlBlock])) {
+    BOOL hostsBlockIsValid = [settings boolForKey: @"ActiveBlockAsWhitelist"] || [hostFileBlockerSet.defaultBlocker containsExpectedRulesForBlocklist: [settings valueForKey: @"ActiveBlocklist"]];
+    if(![pf containsSelfControlBlock] || !hostsBlockIsValid) {
         NSLog(@"INFO: Block is missing in PF or hosts, re-adding...");
         // The firewall is missing at least the block header.  Let's clear everything
         // before we re-add to make sure everything goes smoothly.

SelfControlTests/SCUtilityTests.m

@@ -10,6 +10,7 @@
 #import "SCSentry.h"
 #import "SCErr.h"
 #import "SCSettings.h"
+#import "HostFileBlocker.h"
 
 @interface SCUtilityTests : XCTestCase
 
@@ -164,6 +165,47 @@ - (void) testModernBlockDetection {
     XCTAssert([SCBlockUtilities currentBlockIsExpired]);
 }
 
+- (NSURL*)temporaryHostsFileURLWithName:(NSString*)name contents:(NSString*)contents {
+    NSURL* url = [[NSURL fileURLWithPath: NSTemporaryDirectory()] URLByAppendingPathComponent: name];
+    [contents writeToURL: url atomically: YES encoding: NSUTF8StringEncoding error: nil];
+    return url;
+}
+
+- (void) testHostBlockIntegrityRequiresExpectedRules {
+    NSURL* hostsURL = [self temporaryHostsFileURLWithName: @"selfcontrol-empty-hosts-block-test"
+                                                 contents: @"127.0.0.1 localhost\n\n# BEGIN SELFCONTROL BLOCK\n# END SELFCONTROL BLOCK\n"];
+    HostFileBlocker* blocker = [[HostFileBlocker alloc] initWithPath: hostsURL.path];
+
+    XCTAssert([blocker containsSelfControlBlock]);
+    XCTAssertFalse([blocker containsExpectedRulesForBlocklist: @[ @"youtube.com" ]]);
+
+    [[NSFileManager defaultManager] removeItemAtURL: hostsURL error: nil];
+}
+
+- (void) testHostBlockIntegrityAcceptsExpectedRules {
+    NSURL* hostsURL = [self temporaryHostsFileURLWithName: @"selfcontrol-valid-hosts-block-test"
+                                                 contents: @"127.0.0.1 localhost\n"];
+    HostFileBlocker* blocker = [[HostFileBlocker alloc] initWithPath: hostsURL.path];
+    [blocker addSelfControlBlockHeader];
+    [blocker addRuleBlockingDomain: @"youtube.com"];
+    [blocker addSelfControlBlockFooter];
+
+    XCTAssert([blocker containsExpectedRulesForBlocklist: @[ @"youtube.com" ]]);
+    XCTAssertFalse([blocker containsExpectedRulesForBlocklist: @[ @"youtube.com", @"www.youtube.com" ]]);
+
+    [[NSFileManager defaultManager] removeItemAtURL: hostsURL error: nil];
+}
+
+- (void) testHostBlockIntegrityIgnoresRulesHostsCannotRepresent {
+    NSURL* hostsURL = [self temporaryHostsFileURLWithName: @"selfcontrol-hosts-unrepresentable-rules-test"
+                                                 contents: @"127.0.0.1 localhost\n\n# BEGIN SELFCONTROL BLOCK\n# END SELFCONTROL BLOCK\n"];
+    HostFileBlocker* blocker = [[HostFileBlocker alloc] initWithPath: hostsURL.path];
+
+    XCTAssert([blocker containsExpectedRulesForBlocklist: @[ @"*.youtube.com", @"127.0.0.1", @"example.com:443" ]]);
+
+    [[NSFileManager defaultManager] removeItemAtURL: hostsURL error: nil];
+}
+
 - (void) testLegacyBlockDetection {
     // test blockIsRunningInLegacyDictionary
     // the block is "running" even if it's expired, since it hasn't been removed