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Commit 4eabbe3f authored by Luke Huang's avatar Luke Huang
Browse files

Fix the side channel attack by using aysnc DnsResolver API with FLAG_NO_CACHE_STORE 

Before this CL, FLAG_NO_CACHE_STORE could be used to perform side
channel attack. Because this flag ensures the result is never
added to the cache, but will return a cached response if one exists.
So make FLAG_NO_CACHE_STORE imply FLAG_NO_CACHE_LOOKUP to block the
possibility of side channel attacking.

Bug: 150371903
Test: atest
Change-Id: I37391ffe315b90c0cdfd86888c6bf68b2b89f601
parent 0986cbb7

res_cache.cpp

+4 −6
Original line number Diff line number Diff line
@@ -1190,7 +1190,9 @@ ResolvCacheStatus resolv_cache_lookup(unsigned netid, const void* query, int que 
    // possible to cache the answer of this query.

    // If ANDROID_RESOLV_NO_CACHE_STORE is set, return RESOLV_CACHE_SKIP to skip possible cache

    // storing.

    if (flags & ANDROID_RESOLV_NO_CACHE_LOOKUP) {

    // (b/150371903): ANDROID_RESOLV_NO_CACHE_STORE should imply ANDROID_RESOLV_NO_CACHE_LOOKUP

    // to avoid side channel attack.

    if (flags & (ANDROID_RESOLV_NO_CACHE_LOOKUP | ANDROID_RESOLV_NO_CACHE_STORE)) {

        return flags & ANDROID_RESOLV_NO_CACHE_STORE ? RESOLV_CACHE_SKIP : RESOLV_CACHE_NOTFOUND;

    }

    Entry key;
@@ -1221,10 +1223,6 @@ ResolvCacheStatus resolv_cache_lookup(unsigned netid, const void* query, int que 


    if (e == NULL) {

        LOG(INFO) << __func__ << ": NOT IN CACHE";

        // If it is no-cache-store mode, we won't wait for possible query.

        if (flags & ANDROID_RESOLV_NO_CACHE_STORE) {

            return RESOLV_CACHE_SKIP;

        }



        if (!cache_has_pending_request_locked(cache, &key, true)) {

            return RESOLV_CACHE_NOTFOUND;
@@ -1264,7 +1262,7 @@ ResolvCacheStatus resolv_cache_lookup(unsigned netid, const void* query, int que 
        LOG(INFO) << __func__ << ": NOT IN CACHE (STALE ENTRY " << *lookup << "DISCARDED)";

        res_pquery(e->query, e->querylen);

        _cache_remove_p(cache, lookup);

        return (flags & ANDROID_RESOLV_NO_CACHE_STORE) ? RESOLV_CACHE_SKIP : RESOLV_CACHE_NOTFOUND;

        return RESOLV_CACHE_NOTFOUND;

    }



    *answerlen = e->answerlen;

resolv_cache_unit_test.cpp

+1 −1
Original line number Diff line number Diff line
@@ -353,7 +353,7 @@ TEST_F(ResolvCacheTest, CacheLookup_CacheFlags) { 
    EXPECT_TRUE(cacheLookup(RESOLV_CACHE_NOTFOUND, TEST_NETID, ce, ANDROID_RESOLV_NO_CACHE_LOOKUP));



    // Now no-cache-store has no effect if a same entry is existent in the cache.

    EXPECT_TRUE(cacheLookup(RESOLV_CACHE_FOUND, TEST_NETID, ce, ANDROID_RESOLV_NO_CACHE_STORE));

    EXPECT_TRUE(cacheLookup(RESOLV_CACHE_SKIP, TEST_NETID, ce, ANDROID_RESOLV_NO_CACHE_STORE));



    // Skip the cache lookup again regardless of a same entry being already in the cache.

    EXPECT_TRUE(cacheLookup(RESOLV_CACHE_SKIP, TEST_NETID, ce,

tests/resolv_integration_test.cpp

+49 −39
Original line number Diff line number Diff line
@@ -2238,13 +2238,13 @@ TEST_F(ResolverTest, Async_MalformedQuery) { 


TEST_F(ResolverTest, Async_CacheFlags) {

    constexpr char listen_addr[] = "127.0.0.4";

    constexpr char host_name[] = "howdy.example.com.";

    constexpr char another_host_name[] = "howdy.example2.com.";

    constexpr char host_name1[] = "howdy.example.com.";

    constexpr char host_name2[] = "howdy.example2.com.";

    constexpr char host_name3[] = "howdy.example3.com.";

    const std::vector<DnsRecord> records = {

            {host_name, ns_type::ns_t_a, "1.2.3.4"},

            {host_name, ns_type::ns_t_aaaa, "::1.2.3.4"},

            {another_host_name, ns_type::ns_t_a, "1.2.3.5"},

            {another_host_name, ns_type::ns_t_aaaa, "::1.2.3.5"},

            {host_name1, ns_type::ns_t_a, "1.2.3.4"}, {host_name1, ns_type::ns_t_aaaa, "::1.2.3.4"},

            {host_name2, ns_type::ns_t_a, "1.2.3.5"}, {host_name2, ns_type::ns_t_aaaa, "::1.2.3.5"},

            {host_name3, ns_type::ns_t_a, "1.2.3.6"}, {host_name3, ns_type::ns_t_aaaa, "::1.2.3.6"},

    };



    test::DNSResponder dns(listen_addr);
@@ -2268,17 +2268,28 @@ TEST_F(ResolverTest, Async_CacheFlags) { 
    expectAnswersValid(fd1, AF_INET, "1.2.3.4");



    // No cache exists, expect 3 queries

    EXPECT_EQ(3U, GetNumQueries(dns, host_name));

    EXPECT_EQ(3U, GetNumQueries(dns, host_name1));



    // Re-query and cache

    // Raise a query with no flags to ensure no cache exists. Also make an cache entry for the

    // query.

    fd1 = resNetworkQuery(TEST_NETID, "howdy.example.com", ns_c_in, ns_t_a, 0);



    EXPECT_TRUE(fd1 != -1);



    expectAnswersValid(fd1, AF_INET, "1.2.3.4");



    // Now we have cache, expect 4 queries

    EXPECT_EQ(4U, GetNumQueries(dns, host_name));

    // Expect 4 queries because there should be no cache before this query.

    EXPECT_EQ(4U, GetNumQueries(dns, host_name1));



    // Now we have the cache entry, re-query with ANDROID_RESOLV_NO_CACHE_STORE to ensure

    // that ANDROID_RESOLV_NO_CACHE_STORE implied ANDROID_RESOLV_NO_CACHE_LOOKUP.

    fd1 = resNetworkQuery(TEST_NETID, "howdy.example.com", ns_c_in, ns_t_a,

                          ANDROID_RESOLV_NO_CACHE_STORE);

    EXPECT_TRUE(fd1 != -1);

    expectAnswersValid(fd1, AF_INET, "1.2.3.4");

    // Expect 5 queries because we shouldn't do cache lookup for the query which has

    // ANDROID_RESOLV_NO_CACHE_STORE.

    EXPECT_EQ(5U, GetNumQueries(dns, host_name1));



    // ANDROID_RESOLV_NO_CACHE_LOOKUP

    fd1 = resNetworkQuery(TEST_NETID, "howdy.example.com", ns_c_in, ns_t_a,
@@ -2292,78 +2303,77 @@ TEST_F(ResolverTest, Async_CacheFlags) { 
    expectAnswersValid(fd2, AF_INET, "1.2.3.4");

    expectAnswersValid(fd1, AF_INET, "1.2.3.4");



    // Skip cache, expect 6 queries

    EXPECT_EQ(6U, GetNumQueries(dns, host_name));

    // Cache was skipped, expect 2 more queries.

    EXPECT_EQ(7U, GetNumQueries(dns, host_name1));



    // Re-query verify cache works

    fd1 = resNetworkQuery(TEST_NETID, "howdy.example.com", ns_c_in, ns_t_a,

                          ANDROID_RESOLV_NO_CACHE_STORE);

    fd1 = resNetworkQuery(TEST_NETID, "howdy.example.com", ns_c_in, ns_t_a, 0);

    EXPECT_TRUE(fd1 != -1);

    expectAnswersValid(fd1, AF_INET, "1.2.3.4");



    // Cache hits,  expect still 6 queries

    EXPECT_EQ(6U, GetNumQueries(dns, host_name));

    // Cache hits,  expect still 7 queries

    EXPECT_EQ(7U, GetNumQueries(dns, host_name1));



    // Start to verify if ANDROID_RESOLV_NO_CACHE_LOOKUP does write response into cache

    dns.clearQueries();



    fd1 = resNetworkQuery(TEST_NETID, "howdy.example.com", ns_c_in, ns_t_aaaa,

    fd1 = resNetworkQuery(TEST_NETID, "howdy.example2.com", ns_c_in, ns_t_aaaa,

                          ANDROID_RESOLV_NO_CACHE_LOOKUP);

    fd2 = resNetworkQuery(TEST_NETID, "howdy.example.com", ns_c_in, ns_t_aaaa,

    fd2 = resNetworkQuery(TEST_NETID, "howdy.example2.com", ns_c_in, ns_t_aaaa,

                          ANDROID_RESOLV_NO_CACHE_LOOKUP);



    EXPECT_TRUE(fd1 != -1);

    EXPECT_TRUE(fd2 != -1);



    expectAnswersValid(fd2, AF_INET6, "::1.2.3.4");

    expectAnswersValid(fd1, AF_INET6, "::1.2.3.4");

    expectAnswersValid(fd2, AF_INET6, "::1.2.3.5");

    expectAnswersValid(fd1, AF_INET6, "::1.2.3.5");



    // Skip cache, expect 2 queries

    EXPECT_EQ(2U, GetNumQueries(dns, host_name));

    EXPECT_EQ(2U, GetNumQueries(dns, host_name2));



    // Re-query without flags

    fd1 = resNetworkQuery(TEST_NETID, "howdy.example.com", ns_c_in, ns_t_aaaa, 0);

    fd2 = resNetworkQuery(TEST_NETID, "howdy.example.com", ns_c_in, ns_t_aaaa, 0);

    fd1 = resNetworkQuery(TEST_NETID, "howdy.example2.com", ns_c_in, ns_t_aaaa, 0);

    fd2 = resNetworkQuery(TEST_NETID, "howdy.example2.com", ns_c_in, ns_t_aaaa, 0);



    EXPECT_TRUE(fd1 != -1);

    EXPECT_TRUE(fd2 != -1);



    expectAnswersValid(fd2, AF_INET6, "::1.2.3.4");

    expectAnswersValid(fd1, AF_INET6, "::1.2.3.4");

    expectAnswersValid(fd2, AF_INET6, "::1.2.3.5");

    expectAnswersValid(fd1, AF_INET6, "::1.2.3.5");



    // Cache hits, expect still 2 queries

    EXPECT_EQ(2U, GetNumQueries(dns, host_name));

    EXPECT_EQ(2U, GetNumQueries(dns, host_name2));



    // Test both ANDROID_RESOLV_NO_CACHE_STORE and ANDROID_RESOLV_NO_CACHE_LOOKUP are set

    dns.clearQueries();



    // Make sure that the cache of "howdy.example2.com" exists.

    fd1 = resNetworkQuery(TEST_NETID, "howdy.example2.com", ns_c_in, ns_t_aaaa, 0);

    // Make sure that the cache of "howdy.example3.com" exists.

    fd1 = resNetworkQuery(TEST_NETID, "howdy.example3.com", ns_c_in, ns_t_aaaa, 0);

    EXPECT_TRUE(fd1 != -1);

    expectAnswersValid(fd1, AF_INET6, "::1.2.3.5");

    EXPECT_EQ(1U, GetNumQueries(dns, another_host_name));

    expectAnswersValid(fd1, AF_INET6, "::1.2.3.6");

    EXPECT_EQ(1U, GetNumQueries(dns, host_name3));



    // Re-query with testFlags

    const int testFlag = ANDROID_RESOLV_NO_CACHE_STORE | ANDROID_RESOLV_NO_CACHE_LOOKUP;

    fd1 = resNetworkQuery(TEST_NETID, "howdy.example2.com", ns_c_in, ns_t_aaaa, testFlag);

    fd1 = resNetworkQuery(TEST_NETID, "howdy.example3.com", ns_c_in, ns_t_aaaa, testFlag);

    EXPECT_TRUE(fd1 != -1);

    expectAnswersValid(fd1, AF_INET6, "::1.2.3.5");

    expectAnswersValid(fd1, AF_INET6, "::1.2.3.6");

    // Expect cache lookup is skipped.

    EXPECT_EQ(2U, GetNumQueries(dns, another_host_name));

    EXPECT_EQ(2U, GetNumQueries(dns, host_name3));



    // Do another query with testFlags

    fd1 = resNetworkQuery(TEST_NETID, "howdy.example2.com", ns_c_in, ns_t_a, testFlag);

    fd1 = resNetworkQuery(TEST_NETID, "howdy.example3.com", ns_c_in, ns_t_a, testFlag);

    EXPECT_TRUE(fd1 != -1);

    expectAnswersValid(fd1, AF_INET, "1.2.3.5");

    expectAnswersValid(fd1, AF_INET, "1.2.3.6");

    // Expect cache lookup is skipped.

    EXPECT_EQ(3U, GetNumQueries(dns, another_host_name));

    EXPECT_EQ(3U, GetNumQueries(dns, host_name3));



    // Re-query with no flags

    fd1 = resNetworkQuery(TEST_NETID, "howdy.example2.com", ns_c_in, ns_t_a, 0);

    fd1 = resNetworkQuery(TEST_NETID, "howdy.example3.com", ns_c_in, ns_t_a, 0);

    EXPECT_TRUE(fd1 != -1);

    expectAnswersValid(fd1, AF_INET, "1.2.3.5");

    expectAnswersValid(fd1, AF_INET, "1.2.3.6");

    // Expect no cache hit because cache storing is also skipped in previous query.

    EXPECT_EQ(4U, GetNumQueries(dns, another_host_name));

    EXPECT_EQ(4U, GetNumQueries(dns, host_name3));

}



TEST_F(ResolverTest, Async_NoCacheStoreFlagDoesNotRefreshStaleCacheEntry) {