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authorJulian Andres Klode <jak@debian.org>2017-01-29 13:05:18 +0100
committerJulian Andres Klode <julian.klode@canonical.com>2018-08-07 15:07:52 +0200
commitc2c8b4787b0882234ba2772ec7513afbf97b563a (patch)
treef6c0634c45d174c00192356c49a3fd7fe583e396 /apt-pkg
parent91671efc7f63b3e2ff2a573d86ac3225e9b5f9cd (diff)
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]
Diffstat (limited to 'apt-pkg')
-rw-r--r--apt-pkg/deb/debsystem.cc53
-rw-r--r--apt-pkg/deb/debsystem.h4
-rw-r--r--apt-pkg/deb/dpkgpm.cc4
-rw-r--r--apt-pkg/pkgsystem.cc25
-rw-r--r--apt-pkg/pkgsystem.h12
5 files changed, 91 insertions, 7 deletions
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 /*{{{*/
// ---------------------------------------------------------------------
@@ -129,12 +153,27 @@ 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<std::string> const &sArgs, int * const inputFd, int * const outputFd, bool const DiscardOutput);
APT_HIDDEN static bool SupportsMultiArch();
APT_HIDDEN static std::vector<std::string> 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<debSystem*>(_system) != nullptr
+ && dynamic_cast<debSystem*>(_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 efbaddcdb..eaa3f5ab7 100644
--- a/apt-pkg/pkgsystem.cc
+++ b/apt-pkg/pkgsystem.cc
@@ -12,6 +12,7 @@
#include <config.h>
#include <apt-pkg/debsystem.h>
+#include <apt-pkg/error.h>
#include <apt-pkg/macros.h>
#include <apt-pkg/pkgsystem.h>
@@ -85,4 +86,28 @@ map_id_t pkgSystem::GetVersionMapping(map_id_t const in) const
}
/*}}}*/
+bool pkgSystem::LockInner() /*{{{*/
+{
+ debSystem * const deb = dynamic_cast<debSystem *>(this);
+ if (deb != NULL)
+ return deb->LockInner();
+ return _error->Error("LockInner is not implemented");
+}
+ /*}}}*/
+bool pkgSystem::UnLockInner(bool NoErrors) /*{{{*/
+{
+ debSystem * const deb = dynamic_cast<debSystem *>(this);
+ if (deb != NULL)
+ return deb->UnLockInner(NoErrors);
+ return _error->Error("UnLockInner is not implemented");
+}
+ /*}}}*/
+bool pkgSystem::IsLocked() /*{{{*/
+{
+ debSystem * const deb = dynamic_cast<debSystem *>(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;
};