From c2c8b4787b0882234ba2772ec7513afbf97b563a 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] --- apt-pkg/deb/debsystem.cc | 53 +++++++++++++++++++++++++++++++++++++++++------- apt-pkg/deb/debsystem.h | 4 ++++ apt-pkg/deb/dpkgpm.cc | 4 ++++ 3 files changed, 54 insertions(+), 7 deletions(-) (limited to 'apt-pkg/deb') diff --git a/apt-pkg/deb/debsystem.cc b/apt-pkg/deb/debsystem.cc index c183ab000..11aa2cfd7 100644 --- a/apt-pkg/deb/debsystem.cc +++ b/apt-pkg/deb/debsystem.cc @@ -44,10 +44,11 @@ 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; @@ -85,21 +86,29 @@ 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) @@ -116,6 +125,21 @@ 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 /*{{{*/ // --------------------------------------------------------------------- @@ -129,11 +153,26 @@ 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 7b59fc073..4503676fa 100644 --- a/apt-pkg/deb/debsystem.h +++ b/apt-pkg/deb/debsystem.h @@ -50,6 +50,10 @@ 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); -- cgit v1.2.3