Fix 32-bit userspace on 64-bit kernel quota2 compatibility.

#include <netinet/in.h>

#include <stdlib.h>

#include <string.h>

#include <sys/personality.h>

#include <sys/socket.h>

#include <sys/types.h>

#include <sys/utsname.h>

#include <android-base/parseint.h>

#include <log/log.h>

#include <sysutils/NetlinkEvent.h>

using android::base::ParseInt;

/* From kernel's net/netfilter/xt_quota2.c */

const int LOCAL_QLOG_NL_EVENT = 112;

const int LOCAL_NFLOG_PACKET = NFNL_SUBSYS_ULOG << 8 | NFULNL_MSG_PACKET;

/* From deprecated ipt_ULOG.h to parse QLOG_NL_EVENT. */

/******************************************************************************

 * WARNING: HERE BE DRAGONS!                                                  *

 *                                                                            *

 * This is here to provide for compatibility with both 32 and 64-bit kernels  *

 * from 32-bit userspace.                                                     *

 *                                                                            *

 * The kernel definition of this struct uses types (like long) that are not   *

 * the same across 32-bit and 64-bit builds, and there is no compatibility    *

 * layer to fix it up before it reaches userspace.                            *

 * As such we need to detect the bit-ness of the kernel and deal with it.     *

 *                                                                            *

 ******************************************************************************/

/*

 * This is the verbatim kernel declaration from net/netfilter/xt_quota2.c,

 * it is *NOT* of a well defined layout and is included here for compile

 * time assertions only.

 *

 * It got there from deprecated ipt_ULOG.h to parse QLOG_NL_EVENT.

 */

#define ULOG_MAC_LEN 80

#define ULOG_PREFIX_LEN 32

typedef struct ulog_packet_msg {

    unsigned char payload[0];

} ulog_packet_msg_t;

#include <android-base/parseint.h>

#include <log/log.h>

#include <sysutils/NetlinkEvent.h>

using android::base::ParseInt;

// On Linux int is always 32 bits, while sizeof(long) == sizeof(void*),

// thus long on a 32-bit Linux kernel is 32-bits, like int always is

typedef int long32;

typedef unsigned int ulong32;

static_assert(sizeof(long32) == 4);

static_assert(sizeof(ulong32) == 4);

// Here's the same structure definition with the assumption the kernel

// is compiled for 32-bits.

typedef struct {

    ulong32 mark;

    long32 timestamp_sec;

    long32 timestamp_usec;

    unsigned int hook;

    char indev_name[IFNAMSIZ];

    char outdev_name[IFNAMSIZ];

    ulong32 data_len;

    char prefix[ULOG_PREFIX_LEN];

    unsigned char mac_len;

    unsigned char mac[ULOG_MAC_LEN];

    unsigned char payload[0];

} ulog_packet_msg32_t;

// long on a 64-bit kernel is 64-bits with 64-bit alignment,

// while long long is 64-bit but may have 32-bit aligment.

typedef long long __attribute__((__aligned__(8))) long64;

typedef unsigned long long __attribute__((__aligned__(8))) ulong64;

static_assert(sizeof(long64) == 8);

static_assert(sizeof(ulong64) == 8);

// Here's the same structure definition with the assumption the kernel

// is compiled for 64-bits.

typedef struct {

    ulong64 mark;

    long64 timestamp_sec;

    long64 timestamp_usec;

    unsigned int hook;

    char indev_name[IFNAMSIZ];

    char outdev_name[IFNAMSIZ];

    ulong64 data_len;

    char prefix[ULOG_PREFIX_LEN];

    unsigned char mac_len;

    unsigned char mac[ULOG_MAC_LEN];

    unsigned char payload[0];

} ulog_packet_msg64_t;

// One expects the 32-bit version to be smaller than the 64-bit version.

static_assert(sizeof(ulog_packet_msg32_t) < sizeof(ulog_packet_msg64_t));

// And either way the 'native' version should match either the 32 or 64 bit one.

static_assert(sizeof(ulog_packet_msg_t) == sizeof(ulog_packet_msg32_t) ||

              sizeof(ulog_packet_msg_t) == sizeof(ulog_packet_msg64_t));

// In practice these sizes are always simply (for both x86 and arm):

static_assert(sizeof(ulog_packet_msg32_t) == 168);

static_assert(sizeof(ulog_packet_msg64_t) == 192);

// Figure out the bitness of userspace.

// Trivial and known at compile time.

static bool isUserspace64bit(void) {

    return sizeof(long) == 8;

}

// Figure out the bitness of the kernel.

static bool isKernel64Bit(void) {

    // a 64-bit userspace requires a 64-bit kernel

    if (isUserspace64bit()) return true;

    static bool init = false;

    static bool cache = false;

    if (init) return cache;

    // Retrieve current personality - on Linux this system call *cannot* fail.

    int p = personality(0xffffffff);

    // But if it does just assume kernel and userspace (which is 32-bit) match...

    if (p == -1) return false;

    // This will effectively mask out the bottom 8 bits, and switch to 'native'

    // personality, and then return the previous personality of this thread

    // (likely PER_LINUX or PER_LINUX32) with any extra options unmodified.

    int q = personality((p & ~PER_MASK) | PER_LINUX);

    // Per man page this theoretically could error out with EINVAL,

    // but kernel code analysis suggests setting PER_LINUX cannot fail.

    // Either way, assume kernel and userspace (which is 32-bit) match...

    if (q != p) return false;

    struct utsname u;

    (void)uname(&u);  // only possible failure is EFAULT, but u is on stack.

    // Switch back to previous personality.

    // Theoretically could fail with EINVAL on arm64 with no 32-bit support,

    // but then we wouldn't have fetched 'p' from the kernel in the first place.

    // Either way there's nothing meaningul we can do in case of error.

    // Since PER_LINUX32 vs PER_LINUX only affects uname.machine it doesn't

    // really hurt us either.  We're really just switching back to be 'clean'.

    (void)personality(p);

    // Possible values of utsname.machine observed on x86_64 desktop (arm via qemu):

    //   x86_64 i686 aarch64 armv7l

    // additionally observed on arm device:

    //   armv8l

    // presumably also might just be possible:

    //   i386 i486 i586

    // and there might be other weird arm32 cases.

    // We note that the 64 is present in both 64-bit archs,

    // and in general is likely to be present in only 64-bit archs.

    cache = !!strstr(u.machine, "64");

    init = true;

    return cache;

}

/******************************************************************************/

NetlinkEvent::NetlinkEvent() {

    mAction = Action::kUnknown;

 * Parse a QLOG_NL_EVENT message.

 */

bool NetlinkEvent::parseUlogPacketMessage(const struct nlmsghdr *nh) {

    const char* alert;

    const char* devname;

    ulog_packet_msg_t *pm = (ulog_packet_msg_t *) NLMSG_DATA(nh);

    if (!checkRtNetlinkLength(nh, sizeof(*pm)))

        return false;

    devname = pm->indev_name[0] ? pm->indev_name : pm->outdev_name;

    asprintf(&mParams[0], "ALERT_NAME=%s", pm->prefix);

    if (isKernel64Bit()) {

        ulog_packet_msg64_t* pm64 = (ulog_packet_msg64_t*)NLMSG_DATA(nh);

        if (!checkRtNetlinkLength(nh, sizeof(*pm64))) return false;

        alert = pm64->prefix;

        devname = pm64->indev_name[0] ? pm64->indev_name : pm64->outdev_name;

    } else {

        ulog_packet_msg32_t* pm32 = (ulog_packet_msg32_t*)NLMSG_DATA(nh);

        if (!checkRtNetlinkLength(nh, sizeof(*pm32))) return false;

        alert = pm32->prefix;

        devname = pm32->indev_name[0] ? pm32->indev_name : pm32->outdev_name;

    }

    asprintf(&mParams[0], "ALERT_NAME=%s", alert);

    asprintf(&mParams[1], "INTERFACE=%s", devname);

    mSubsystem = strdup("qlog");

    mAction = Action::kChange;