forked from lix-project/lix
eldritch horrors
3d155fc509
copy-constructing or assigning from pid_t can easily lead to duplicate
Pid instances for the same process if a pid_t was used carelessly, and
Pid itself was copy-constructible. both could cause surprising results
such as killing processes twice (which could become very problemantic,
but luckily modern systems don't reuse PIDs all that quickly), or more
than one piece of the code believing it owns a process when neither do
Change-Id: Ifea7445f84200b34c1a1d0acc2cdffe0f01e20c6
117 lines
3.7 KiB
C++
117 lines
3.7 KiB
C++
#include "file-system.hh"
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#include "processes.hh"
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#include "unix-domain-socket.hh"
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#include "strings.hh"
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#include <sys/socket.h>
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#include <sys/un.h>
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#include <unistd.h>
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namespace nix {
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AutoCloseFD createUnixDomainSocket()
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{
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AutoCloseFD fdSocket{socket(PF_UNIX, SOCK_STREAM
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#ifdef SOCK_CLOEXEC
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| SOCK_CLOEXEC
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#endif
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, 0)};
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if (!fdSocket)
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throw SysError("cannot create Unix domain socket");
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closeOnExec(fdSocket.get());
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return fdSocket;
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}
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AutoCloseFD createUnixDomainSocket(const Path & path, mode_t mode)
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{
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auto fdSocket = nix::createUnixDomainSocket();
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bind(fdSocket.get(), path);
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chmodPath(path.c_str(), mode);
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if (listen(fdSocket.get(), 100) == -1)
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throw SysError("cannot listen on socket '%1%'", path);
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return fdSocket;
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}
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/**
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* Workaround for the max length of Unix socket names being between 102
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* (darwin) and 108 (Linux), which is extremely short. This limitation is
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* caused by historical restrictions on sizeof(struct sockaddr):
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* https://unix.stackexchange.com/a/367012.
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*
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* Our solution here is to start a process inheriting the socket, chdir into
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* the directory of the socket, then connect with just the filename. This is
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* rather silly but it works around working directory being process-wide state,
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* and is as clearly sound as possible.
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*/
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static void bindConnectProcHelper(
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std::string_view operationName, auto && operation,
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int fd, const std::string & path)
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{
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struct sockaddr_un addr;
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addr.sun_family = AF_UNIX;
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// Casting between types like these legacy C library interfaces
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// require is forbidden in C++. To maintain backwards
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// compatibility, the implementation of the bind/connect functions
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// contains some hints to the compiler that allow for this
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// special case.
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auto * psaddr = reinterpret_cast<struct sockaddr *>(&addr);
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if (path.size() + 1 >= sizeof(addr.sun_path)) {
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Pipe pipe;
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pipe.create();
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Pid pid{startProcess([&] {
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try {
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pipe.readSide.close();
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Path dir = dirOf(path);
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if (chdir(dir.c_str()) == -1)
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throw SysError("chdir to '%s' failed", dir);
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std::string base(baseNameOf(path));
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if (base.size() + 1 >= sizeof(addr.sun_path))
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throw Error("socket path '%s' is too long", base);
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memcpy(addr.sun_path, base.c_str(), base.size() + 1);
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if (operation(fd, psaddr, sizeof(addr)) == -1)
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throw SysError("cannot %s to socket at '%s'", operationName, path);
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writeFull(pipe.writeSide.get(), "0\n");
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} catch (SysError & e) {
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writeFull(pipe.writeSide.get(), fmt("%d\n", e.errNo));
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} catch (...) {
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writeFull(pipe.writeSide.get(), "-1\n");
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}
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})};
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pipe.writeSide.close();
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auto errNo = string2Int<int>(chomp(drainFD(pipe.readSide.get())));
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if (!errNo || *errNo == -1)
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throw Error("cannot %s to socket at '%s'", operationName, path);
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else if (*errNo > 0) {
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errno = *errNo;
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throw SysError("cannot %s to socket at '%s'", operationName, path);
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}
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} else {
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memcpy(addr.sun_path, path.c_str(), path.size() + 1);
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if (operation(fd, psaddr, sizeof(addr)) == -1)
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throw SysError("cannot %s to socket at '%s'", operationName, path);
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}
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}
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void bind(int fd, const std::string & path)
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{
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unlink(path.c_str());
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bindConnectProcHelper("bind", ::bind, fd, path);
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}
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void connect(int fd, const std::string & path)
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{
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bindConnectProcHelper("connect", ::connect, fd, path);
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}
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}
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