From 6c0c94ed32b8e679b14b0f89b51c1c336dc0ab9c Mon Sep 17 00:00:00 2001 From: Julian Andres Klode Date: Sun, 29 Jan 2017 13:05:18 +0100 Subject: Add support for dpkg frontend lock The dpkg frontend lock is a lock dpkg tries to acquire except if the frontend already acquires it. This fixes a race condition in the install command where the dpkg lock is not held for a short period of time between different dpkg invocations. For this reason we also define an environment variable DPKG_FRONTEND_LOCKED for dpkg invocations so dpkg knows not to try to acquire the frontend lock because it's held by a parent process. We can set DPKG_FRONTEND_LOCKED only if the frontend lock really is held; that is, if our lock count is greater than 0 - otherwise an apt client not using the LockInner family of functions would run dpkg without the frontend lock set, but with DPKG_FRONTEND_LOCKED set. Such a process has a weaker guarantee: Because dpkg would not lock the frontend lock either, the process is prone to the existing races, and, more importantly, so is a new style process. Closes: #869546 [fixups: fix error messages, add public IsLocked() method, and make {Un,}LockInner return an error on !debSystem] (cherry picked from commit c2c8b4787b0882234ba2772ec7513afbf97b563a) LP: #1781169 --- apt-pkg/deb/debsystem.cc | 53 ++++++++++++++++++++++++++++++++++++------ apt-pkg/deb/debsystem.h | 4 ++++ apt-pkg/deb/dpkgpm.cc | 4 ++++ apt-pkg/pkgsystem.cc | 25 ++++++++++++++++++++ apt-pkg/pkgsystem.h | 12 ++++++++++ apt-private/private-install.cc | 4 ++-- 6 files changed, 93 insertions(+), 9 deletions(-) diff --git a/apt-pkg/deb/debsystem.cc b/apt-pkg/deb/debsystem.cc index 2bb887e75..ee42cc6a7 100644 --- a/apt-pkg/deb/debsystem.cc +++ b/apt-pkg/deb/debsystem.cc @@ -45,10 +45,11 @@ debSystem debSys; class APT_HIDDEN debSystemPrivate { public: - debSystemPrivate() : LockFD(-1), LockCount(0), StatusFile(0) + debSystemPrivate() : FrontendLockFD(-1), LockFD(-1), LockCount(0), StatusFile(0) { } // For locking support + int FrontendLockFD; int LockFD; unsigned LockCount; @@ -86,21 +87,29 @@ bool debSystem::Lock() // Create the lockfile string AdminDir = flNotFile(_config->FindFile("Dir::State::status")); - d->LockFD = GetLock(AdminDir + "lock"); - if (d->LockFD == -1) + string FrontendLockFile = AdminDir + "lock-frontend"; + d->FrontendLockFD = GetLock(FrontendLockFile); + if (d->FrontendLockFD == -1) { if (errno == EACCES || errno == EAGAIN) - return _error->Error(_("Unable to lock the administration directory (%s), " - "is another process using it?"),AdminDir.c_str()); + return _error->Error(_("Unable to acquire the dpkg frontend lock (%s), " + "is another process using it?"),FrontendLockFile.c_str()); else - return _error->Error(_("Unable to lock the administration directory (%s), " - "are you root?"),AdminDir.c_str()); + return _error->Error(_("Unable to acquire the dpkg frontend lock (%s), " + "are you root?"),FrontendLockFile.c_str()); + } + if (LockInner() == false) + { + close(d->FrontendLockFD); + return false; } // See if we need to abort with a dirty journal if (CheckUpdates() == true) { close(d->LockFD); + close(d->FrontendLockFD); + d->FrontendLockFD = -1; d->LockFD = -1; const char *cmd; if (getenv("SUDO_USER") != NULL) @@ -117,6 +126,21 @@ bool debSystem::Lock() return true; } + +bool debSystem::LockInner() { + string AdminDir = flNotFile(_config->FindFile("Dir::State::status")); + d->LockFD = GetLock(AdminDir + "lock"); + if (d->LockFD == -1) + { + if (errno == EACCES || errno == EAGAIN) + return _error->Error(_("Unable to lock the administration directory (%s), " + "is another process using it?"),AdminDir.c_str()); + else + return _error->Error(_("Unable to lock the administration directory (%s), " + "are you root?"),AdminDir.c_str()); + } + return true; +} /*}}}*/ // System::UnLock - Drop a lock /*{{{*/ // --------------------------------------------------------------------- @@ -130,11 +154,26 @@ bool debSystem::UnLock(bool NoErrors) return _error->Error(_("Not locked")); if (--d->LockCount == 0) { + close(d->FrontendLockFD); close(d->LockFD); d->LockCount = 0; } return true; +} +bool debSystem::UnLockInner(bool NoErrors) { + (void) NoErrors; + close(d->LockFD); + return true; +} + /*}}}*/ +// System::IsLocked - Check if system is locked /*{{{*/ +// --------------------------------------------------------------------- +/* This checks if the frontend lock is hold. The inner lock might be + * released. */ +bool debSystem::IsLocked() +{ + return d->LockCount > 0; } /*}}}*/ // System::CheckUpdates - Check if the updates dir is dirty /*{{{*/ diff --git a/apt-pkg/deb/debsystem.h b/apt-pkg/deb/debsystem.h index 9fdecb42f..9de3c8b4e 100644 --- a/apt-pkg/deb/debsystem.h +++ b/apt-pkg/deb/debsystem.h @@ -51,6 +51,10 @@ class debSystem : public pkgSystem APT_HIDDEN static pid_t ExecDpkg(std::vector const &sArgs, int * const inputFd, int * const outputFd, bool const DiscardOutput); APT_HIDDEN static bool SupportsMultiArch(); APT_HIDDEN static std::vector SupportedArchitectures(); + + APT_HIDDEN bool LockInner(); + APT_HIDDEN bool UnLockInner(bool NoErrors=false); + APT_HIDDEN bool IsLocked(); }; extern debSystem debSys; diff --git a/apt-pkg/deb/dpkgpm.cc b/apt-pkg/deb/dpkgpm.cc index c6900ec77..790019b98 100644 --- a/apt-pkg/deb/dpkgpm.cc +++ b/apt-pkg/deb/dpkgpm.cc @@ -2010,6 +2010,10 @@ bool pkgDPkgPM::Go(APT::Progress::PackageManager *progress) else setenv("DPKG_COLORS", "never", 0); + if (dynamic_cast(_system) != nullptr + && dynamic_cast(_system)->IsLocked() == true) { + setenv("DPKG_FRONTEND_LOCKED", "true", 1); + } execvp(Args[0], (char**) &Args[0]); cerr << "Could not exec dpkg!" << endl; _exit(100); diff --git a/apt-pkg/pkgsystem.cc b/apt-pkg/pkgsystem.cc index 5d74e882b..196439aab 100644 --- a/apt-pkg/pkgsystem.cc +++ b/apt-pkg/pkgsystem.cc @@ -13,6 +13,7 @@ #include #include +#include #include #include @@ -86,4 +87,28 @@ map_id_t pkgSystem::GetVersionMapping(map_id_t const in) const } /*}}}*/ +bool pkgSystem::LockInner() /*{{{*/ +{ + debSystem * const deb = dynamic_cast(this); + if (deb != NULL) + return deb->LockInner(); + return _error->Error("LockInner is not implemented"); +} + /*}}}*/ +bool pkgSystem::UnLockInner(bool NoErrors) /*{{{*/ +{ + debSystem * const deb = dynamic_cast(this); + if (deb != NULL) + return deb->UnLockInner(NoErrors); + return _error->Error("UnLockInner is not implemented"); +} + /*}}}*/ +bool pkgSystem::IsLocked() /*{{{*/ +{ + debSystem * const deb = dynamic_cast(this); + if (deb != NULL) + return deb->IsLocked(); + return true; +} + /*}}}*/ pkgSystem::~pkgSystem() {} diff --git a/apt-pkg/pkgsystem.h b/apt-pkg/pkgsystem.h index 4b13072e2..b42070532 100644 --- a/apt-pkg/pkgsystem.h +++ b/apt-pkg/pkgsystem.h @@ -119,6 +119,18 @@ class pkgSystem pkgSystem(char const * const Label, pkgVersioningSystem * const VS); virtual ~pkgSystem(); + + + /* companions to Lock()/UnLock + * + * These functions can be called prior to calling dpkg to release an inner + * lock without releasing the overall outer lock, so that dpkg can run + * correctly but no other APT instance can acquire the system lock. + */ + bool LockInner(); + bool UnLockInner(bool NoErrors = false); + /// checks if the system is currently locked + bool IsLocked(); private: pkgSystemPrivate * const d; }; diff --git a/apt-private/private-install.cc b/apt-private/private-install.cc index e1beb21c6..041acce0e 100644 --- a/apt-private/private-install.cc +++ b/apt-private/private-install.cc @@ -346,7 +346,7 @@ bool InstallPackages(CacheFile &Cache,bool ShwKept,bool Ask, bool Safety) } auto const progress = APT::Progress::PackageManagerProgressFactory(); - _system->UnLock(); + _system->UnLockInner(); pkgPackageManager::OrderResult const Res = PM->DoInstall(progress); delete progress; @@ -355,7 +355,7 @@ bool InstallPackages(CacheFile &Cache,bool ShwKept,bool Ask, bool Safety) if (Res == pkgPackageManager::Completed) break; - _system->Lock(); + _system->LockInner(); // Reload the fetcher object and loop again for media swapping Fetcher.Shutdown(); -- cgit v1.2.3