src/Instance.cc

   1 /*
   2  * Copyright (C) 1996-2022 The Squid Software Foundation and contributors
   3  *
   4  * Squid software is distributed under GPLv2+ license and includes
   5  * contributions from numerous individuals and organizations.
   6  * Please see the COPYING and CONTRIBUTORS files for details.
   7  */
   8
   9 #include "squid.h"
  10 #include "base/File.h"
  11 #include "DebugMessages.h"
  12 #include "fs_io.h"
  13 #include "Instance.h"
  14 #include "parser/Tokenizer.h"
  15 #include "sbuf/Stream.h"
  16 #include "SquidConfig.h"
  17 #include "tools.h"
  18
  19 #include <cerrno>
  20
  21 /* To support concurrent PID files, convert local statics into PidFile class */
  22
  23 /// Describes the (last) instance PID file being processed.
  24 /// This hack shortens reporting code while keeping its messages consistent.
  25 static SBuf TheFile;
  26
  27 /// PidFilename() helper
  28 /// \returns PID file name or, if PID signaling was disabled, an empty SBuf
  29 static SBuf
  30 PidFilenameCalc()
  31 {
  32     if (!Config.pidFilename || strcmp(Config.pidFilename, "none") == 0)
  33         return SBuf();
  34
  35     // If chroot has been requested, then we first read the PID file before
  36     // chroot() and then create/update it inside a chrooted environment.
  37     // TODO: Consider removing half-baked chroot support from Squid.
  38     extern bool Chrooted;
  39     if (!Config.chroot_dir || Chrooted) // no need to compensate
  40         return SBuf(Config.pidFilename);
  41
  42     SBuf filename;
  43     filename.append(Config.chroot_dir);
  44     filename.append("/");
  45     filename.append(Config.pidFilename);
  46     debugs(50, 3, "outside chroot: " << filename);
  47     return filename;
  48 }
  49
  50 /// \returns PID file description for debugging messages and error reporting
  51 static SBuf
  52 PidFileDescription(const SBuf &filename)
  53 {
  54     return ToSBuf("PID file (", filename, ')');
  55 }
  56
  57 /// Instance entry points are expected to call this first.
  58 /// \returns PidFilenameCalc() result while updating TheFile context
  59 static SBuf
  60 PidFilename()
  61 {
  62     const auto name = PidFilenameCalc();
  63     TheFile = PidFileDescription(name);
  64     return name;
  65 }
  66
  67 /// \returns the PID of another Squid instance (or throws)
  68 static pid_t
  69 GetOtherPid(File &pidFile)
  70 {
  71     const auto input = pidFile.readSmall(1, 32);
  72     int64_t rawPid = -1;
  73
  74     Parser::Tokenizer tok(input);
  75     if (!(tok.int64(rawPid, 10, false) && // PID digits
  76             (tok.skipOne(CharacterSet::CR)||true) && // optional CR (Windows/etc.)
  77             tok.skipOne(CharacterSet::LF) && // required end of line
  78             tok.atEnd())) { // no trailing garbage
  79         throw TexcHere(ToSBuf("Malformed ", TheFile));
  80     }
  81
  82     debugs(50, 7, "found PID " << rawPid << " in " << TheFile);
  83
  84     if (rawPid < 1)
  85         throw TexcHere(ToSBuf("Bad ", TheFile, " contains unreasonably small PID value: ", rawPid));
  86     const auto finalPid = static_cast<pid_t>(rawPid);
  87     if (static_cast<int64_t>(finalPid) != rawPid)
  88         throw TexcHere(ToSBuf("Bad ", TheFile, " contains unreasonably large PID value: ", rawPid));
  89
  90     return finalPid;
  91 }
  92
  93 /// determines whether a given process is running at the time of the call
  94 static bool
  95 ProcessIsRunning(const pid_t pid)
  96 {
  97     const auto result = kill(pid, 0);
  98     const auto savedErrno = errno;
  99     if (result != 0)
 100         debugs(50, 3, "kill(" << pid << ", 0) failed: " << xstrerr(savedErrno));
 101     // if we do not have permissions to signal the process, then it is running
 102     return (result == 0 || savedErrno == EPERM);
 103 }
 104
 105 /// quits if another Squid instance (that owns the given PID file) is running
 106 static void
 107 ThrowIfAlreadyRunningWith(File &pidFile)
 108 {
 109     bool running = false;
 110     SBuf description;
 111     try {
 112         const auto pid = GetOtherPid(pidFile);
 113         description = ToSBuf(TheFile, " with PID ", pid);
 114         running = ProcessIsRunning(pid);
 115     }
 116     catch (const std::exception &ex) {
 117         debugs(50, 5, "assuming no other Squid instance: " << ex.what());
 118         return;
 119     }
 120
 121     if (running)
 122         throw TexcHere(ToSBuf("Squid is already running: Found fresh instance ", description));
 123
 124     debugs(50, 5, "assuming stale instance " << description);
 125 }
 126
 127 pid_t
 128 Instance::Other()
 129 {
 130     const auto filename = PidFilename();
 131     if (filename.isEmpty())
 132         throw TexcHere("no pid_filename configured");
 133
 134     File pidFile(filename, File::Be::ReadOnly().locked());
 135     return GetOtherPid(pidFile);
 136 }
 137
 138 void
 139 Instance::ThrowIfAlreadyRunning()
 140 {
 141     const auto filename = PidFilename();
 142     if (filename.isEmpty())
 143         return; // the check is impossible
 144
 145     if (const auto filePtr = File::Optional(filename, File::Be::ReadOnly().locked())) {
 146         const std::unique_ptr<File> pidFile(filePtr);
 147         ThrowIfAlreadyRunningWith(*pidFile);
 148     } else {
 149         // It is best to assume then to check because checking without a lock
 150         // might lead to false positives that lead to no Squid starting at all!
 151         debugs(50, 5, "cannot lock " << TheFile << "; assuming no other Squid is running");
 152         // If our assumption is false, we will fail to _create_ the PID file,
 153         // and, hence, will not start, allowing that other Squid to run.
 154     }
 155 }
 156
 157 /// ties Instance::WriteOurPid() scheduler and RemoveInstance(void) handler
 158 static SBuf ThePidFileToRemove;
 159
 160 /// atexit() handler; removes the PID file created with Instance::WriteOurPid()
 161 static void
 162 RemoveInstance()
 163 {
 164     if (ThePidFileToRemove.isEmpty()) // not the PidFilename()!
 165         return; // nothing to do
 166
 167     debugs(50, Important(22), "Removing " << PidFileDescription(ThePidFileToRemove));
 168     const char *filename = ThePidFileToRemove.c_str(); // avoid complex operations inside enter_suid()
 169     enter_suid();
 170     safeunlink(filename, 0);
 171     leave_suid();
 172
 173     ThePidFileToRemove.clear();
 174 }
 175
 176 /// creates a PID file; throws on error
 177 void
 178 Instance::WriteOurPid()
 179 {
 180     // Instance code assumes that we do not support PID filename reconfiguration
 181     static bool called = false;
 182     Must(!called);
 183     called = true;
 184
 185     const auto filename = PidFilename();
 186     if (filename.isEmpty())
 187         return; // nothing to do
 188
 189     File pidFile(filename, File::Be::ReadWrite().locked().createdIfMissing().openedByRoot());
 190
 191     // another instance may have started after the caller checked (if it did)
 192     ThrowIfAlreadyRunningWith(pidFile);
 193
 194     /* now we know that we own the PID file created and/or locked above */
 195
 196     // Cleanup is scheduled through atexit() to ensure both:
 197     // - cleanup upon fatal() and similar "unplanned" exits and
 198     // - enter_suid() existence and proper logging support during cleanup.
 199     // Even without PID filename reconfiguration support, we have to remember
 200     // the file name we have used because Config.pidFilename may change!
 201     (void)std::atexit(&RemoveInstance); // failures leave the PID file on disk
 202     ThePidFileToRemove = filename;
 203
 204     /* write our PID to the locked file */
 205     SBuf pidBuf;
 206     pidBuf.Printf("%d\n", static_cast<int>(getpid()));
 207     pidFile.truncate();
 208     pidFile.writeAll(pidBuf);
 209
 210     // We must fsync before releasing the lock or other Squid processes may not see
 211     // our written PID (and decide that they are dealing with a corrupted PID file).
 212     pidFile.synchronize();
 213
 214     debugs(50, Important(23), "Created " << TheFile);
 215 }
 216