Commit 57821d89 authored by Ramon Nou's avatar Ramon Nou
Browse files

fix(malleability): use atomic rename to prevent hostfile race condition 

write_rs_interval_comments now writes to a temporary file and renames it
to the target path instead of truncating the file in place. This prevents
a race condition where concurrently running daemons could observe an empty
or partially written hostfile. Added cleanup for the temporary file on
failure and updated error messages accordingly.
parent 1527977f

src/common/malleability_markers.cpp

+27 −3
Original line number Diff line number Diff line
@@ -33,9 +33,12 @@ 
#include <stdexcept>

#include <algorithm>

#include <cstring>

#include <cstdio>

#include <iomanip>

#include <fmt/format.h>



#include <unistd.h>



namespace gkfs {

namespace malleable {
@@ -258,11 +261,17 @@ write_rs_interval_comments( 
    }

    in.close();



    std::ofstream out(path, std::ios::trunc);

    // Write to a sibling temporary file and rename it into place.  Mutate

    // start sends this shared hostfile to every daemon concurrently; opening

    // the destination with std::ios::trunc leaves a window in which a peer can

    // observe an empty or partially-written hostfile.

    const auto temporary_path =

            path + ".tmp." + std::to_string(static_cast<long long>(getpid()));

    std::ofstream out(temporary_path, std::ios::trunc);

    if(!out.is_open()) {

        throw std::runtime_error(fmt::format(

                "Failed to write hostfile for RS intervals: '{}': {}", path,

                strerror(errno)));

                "Failed to write temporary hostfile for RS intervals: '{}': {}",

                temporary_path, strerror(errno)));

    }

    for(const auto& kept_line : lines) {

        out << kept_line << "\n";
@@ -272,6 +281,21 @@ write_rs_interval_comments( 
            << " start=" << std::fixed << std::setprecision(9) << interval.start

            << " end=" << interval.end << "\n";

    }

    out.close();

    if(!out) {

        std::remove(temporary_path.c_str());

        throw std::runtime_error(fmt::format(

                "Failed to write temporary hostfile for RS intervals: '{}': {}",

                temporary_path, strerror(errno)));

    }



    if(std::rename(temporary_path.c_str(), path.c_str()) != 0) {

        const auto error = errno;

        std::remove(temporary_path.c_str());

        throw std::runtime_error(fmt::format(

                "Failed to replace hostfile for RS intervals: '{}': {}", path,

                strerror(error)));

    }

}



} // namespace malleable