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Commit 70931aa0 authored by Luke Huang's avatar Luke Huang
Browse files

Refine asynchronous DNS API flag NO_RETRY behavior 

Previously, query with NO_RETRY flag would try to query all the ns once.
Fix it to try only one DNS server per query.
The server is selected randomly from available nameserver list.

Bug: 122564854

Test: built, flashed, booted
      system/netd/tests/runtests.sh pass
      atest CtsNativeNetDnsTestCases
      atest DnsResolverTest

Change-Id: I489c1762b26dd39014ede85d6b6f0e16051ec5e9
parent b0cbe354

DnsProxyListener.cpp

+20 −7
Original line number Diff line number Diff line
@@ -295,14 +295,25 @@ bool simpleStrtoul(const char* input, IntegralType* output, int base = 10) { 
    return true;

}



bool parseQuery(const uint8_t* msg, size_t msgLen, int* rr_type, std::string* rr_name) {

bool setQueryId(uint8_t* msg, size_t msgLen, uint16_t query_id) {

    if (msgLen < sizeof(HEADER)) {

        errno = EINVAL;

        return false;

    }

    auto hp = reinterpret_cast<HEADER*>(msg);

    hp->id = htons(query_id);

    return true;

}



bool parseQuery(const uint8_t* msg, size_t msgLen, uint16_t* query_id, int* rr_type,

                std::string* rr_name) {

    ns_msg handle;

    ns_rr rr;

    if (ns_initparse((const uint8_t*)msg, msgLen, &handle) < 0 ||

        ns_parserr(&handle, ns_s_qd, 0, &rr) < 0) {

        return false;

    }



    *query_id = ns_msg_id(handle);

    *rr_name = ns_rr_name(rr);

    *rr_type = ns_rr_type(rr);

    return true;
@@ -850,10 +861,11 @@ void DnsProxyListener::ResNSendHandler::run() { 
    const uid_t uid = mClient->getUid();

    int rr_type = 0;

    std::string rr_name;

    uint16_t original_query_id = 0;



    // TODO: Handle the case which is msg contains more than one query

    // Parse and store query type/name

    if (!parseQuery(msg.data(), msgLen, &rr_type, &rr_name)) {

    if (!parseQuery(msg.data(), msgLen, &original_query_id, &rr_type, &rr_name) ||

        !setQueryId(msg.data(), msgLen, arc4random_uniform(65536))) {

        // If the query couldn't be parsed, block the request.

        ALOGW("resnsend: from UID %d, invalid query", uid);

        sendBE32(mClient, -EINVAL);
@@ -890,8 +902,9 @@ void DnsProxyListener::ResNSendHandler::run() { 
        return;

    }



    // Send answer

    if (!sendLenAndData(mClient, nsendAns, ansBuf.data())) {

    // Restore query id and send answer

    if (!setQueryId(ansBuf.data(), nsendAns, original_query_id) ||

        !sendLenAndData(mClient, nsendAns, ansBuf.data())) {

        ALOGW("resnsend: failed to send answer to uid %d: %s", uid, strerror(errno));

        return;

    }

include/netd_resolv/resolv_stub.h

+2 −2
Original line number Diff line number Diff line
@@ -47,7 +47,7 @@ extern struct ResolvStub { 
                                                  res_params* params, res_stats stats[MAXNS],

                                                  int* wait_for_pending_req_timeout_count);



    void (*android_net_res_stats_get_usable_servers)(const res_params* params, res_stats stats[],

    int (*android_net_res_stats_get_usable_servers)(const res_params* params, res_stats stats[],

                                                    int nscount, bool valid_servers[]);



    void (*resolv_delete_cache_for_net)(unsigned netid);

include/netd_resolv/stats.h

+3 −3
Original line number Diff line number Diff line
@@ -55,7 +55,7 @@ LIBNETD_RESOLV_PUBLIC int android_net_res_stats_get_info_for_net( 
        int* wait_for_pending_req_timeout_count);



// Returns an array of bools indicating which servers are considered good

LIBNETD_RESOLV_PUBLIC void android_net_res_stats_get_usable_servers(const res_params* params,

LIBNETD_RESOLV_PUBLIC int android_net_res_stats_get_usable_servers(const res_params* params,

                                                                   res_stats stats[], int nscount,

                                                                   bool valid_servers[]);

res_send.cpp

+19 −1
Original line number Diff line number Diff line
@@ -246,6 +246,15 @@ static int random_bind(int s, int family) { 
}

/* BIONIC-END */



// Disables all nameservers other than selectedServer

static void res_set_usable_server(int selectedServer, int nscount, bool usable_servers[]) {

    int usableIndex = 0;

    for (int ns = 0; ns < nscount; ns++) {

        if (usable_servers[ns]) ++usableIndex;

        if (usableIndex != selectedServer) usable_servers[ns] = false;

    }

}



/* int

 * res_isourserver(ina)

 *	looks up "ina" in _res.ns_addr_list[]
@@ -493,7 +502,16 @@ int res_nsend(res_state statp, const u_char* buf, int buflen, u_char* ans, int a 
        return -ESRCH;

    }

    bool usable_servers[MAXNS];

    android_net_res_stats_get_usable_servers(&params, stats, statp->nscount, usable_servers);

    int usableServersCount = android_net_res_stats_get_usable_servers(

            &params, stats, statp->nscount, usable_servers);



    if ((flags & ANDROID_RESOLV_NO_RETRY) && usableServersCount > 1) {

        auto hp = reinterpret_cast<const HEADER*>(buf);



        // Select a random server based on the query id

        int selectedServer = (hp->id % usableServersCount) + 1;

        res_set_usable_server(selectedServer, statp->nscount, usable_servers);

    }

    if (params.retry_count != 0) statp->retry = params.retry_count;



    /*

res_stats.cpp

+3 −2
Original line number Diff line number Diff line
@@ -144,7 +144,7 @@ static bool res_stats_usable_server(const res_params* params, res_stats* stats) 
    return 1;

}



void android_net_res_stats_get_usable_servers(const res_params* params, res_stats stats[],

int android_net_res_stats_get_usable_servers(const res_params* params, res_stats stats[],

                                             int nscount, bool usable_servers[]) {

    unsigned usable_servers_found = 0;

    for (int ns = 0; ns < nscount; ns++) {
@@ -161,4 +161,5 @@ void android_net_res_stats_get_usable_servers(const res_params* params, res_stat 
            usable_servers[ns] = true;

        }

    }

    return (usable_servers_found == 0) ? nscount : usable_servers_found;

}