Merge "libcutils: Stop checking the uid of netlink messages"

#include <linux/netlink.h>

#include <fstream>

#include <private/android_filesystem_config.h>

namespace {

// Returns the uid of root in the current user namespace.

// Returns AID_OVERFLOWUID if the root user is not mapped in the current

// namespace.

// Returns 0 if the kernel is not user namespace-aware (for backwards

// compatibility) or if AID_OVERFLOWUID could not be validated to match what the

// kernel would return.

uid_t GetRootUid() {

    constexpr uid_t kParentRootUid = 0;

    std::ifstream uid_map_file("/proc/self/uid_map");

    if (!uid_map_file) {

        // The kernel does not support user namespaces.

        return kParentRootUid;

    }

    uid_t current_namespace_uid, parent_namespace_uid;

    uint32_t length;

    while (uid_map_file >> current_namespace_uid >> parent_namespace_uid >> length) {

        // Since kParentRootUid is 0, it should be the first entry in the mapped

        // range.

        if (parent_namespace_uid != kParentRootUid || length < 1) continue;

        return current_namespace_uid;

    }

    // Sanity check: verify that the overflow UID is the one to be returned by

    // the kernel.

    std::ifstream overflowuid_file("/proc/sys/kernel/overflowuid");

    if (!overflowuid_file) {

        // It's better to return 0 in case we cannot make sure that the overflow

        // UID matches.

        return kParentRootUid;

    }

    uid_t kernel_overflow_uid;

    if (!(overflowuid_file >> kernel_overflow_uid) || kernel_overflow_uid != AID_OVERFLOWUID)

        return kParentRootUid;

    // root is unmapped, use the kernel "overflow" uid.

    return AID_OVERFLOWUID;

}

}  // namespace

extern "C" {

/**

}

ssize_t uevent_kernel_recv(int socket, void* buffer, size_t length, bool require_group, uid_t* uid) {

    static const uid_t root_uid = GetRootUid();

    struct iovec iov = {buffer, length};

    struct sockaddr_nl addr;

    char control[CMSG_SPACE(sizeof(struct ucred))];

    cred = (struct ucred*)CMSG_DATA(cmsg);

    *uid = cred->uid;

    if (cred->uid != root_uid) {

        /* ignoring netlink message from non-root user */

        goto out;

    }

    if (addr.nl_pid != 0) {

        /* ignore non-kernel */