allow Pre-Install-Pkgs hooks to get info over an FD != stdin

This adds ::InfoFD option alongside the ::Version one to request sending
the information to the specified FD, by default it is STDIN as it was
the case before.

The environment variable APT_HOOK_INFO_FD contains the FD the data is on as
a confirmation that the APT version used understood the request.

Allowing the hook to choose the FD is needed/helpful e.g. for shellscripts
which have a hard time accessing FDs above 9 (as >= 10 are usually used
 internally by them)

Closes: #671728

3 files changed, 81 insertions, 46 deletions

diff --git a/apt-pkg/deb/dpkgpm.cc b/apt-pkg/deb/dpkgpm.cc
index 959d06455..4b5467eff 100644
--- a/apt-pkg/deb/dpkgpm.cc
+++ b/apt-pkg/deb/dpkgpm.cc
@@ -382,24 +382,32 @@ bool pkgDPkgPM::RunScriptsWithPkgs(const char *Cnf)
       OptSec = "DPkg::Tools::Options::" + string(Opts->Value.c_str(),Pos);
       
       unsigned int Version = _config->FindI(OptSec+"::Version",1);
+      unsigned int InfoFD = _config->FindI(OptSec + "::InfoFD", STDIN_FILENO);
       
       // Create the pipes
       int Pipes[2];
       if (pipe(Pipes) != 0)
 	 return _error->Errno("pipe","Failed to create IPC pipe to subprocess");
-      SetCloseExec(Pipes[0],true);
+      if (InfoFD != (unsigned)Pipes[0])
+	 SetCloseExec(Pipes[0],true);
+      else
+	 _config->Set("APT::Keep-Fds::", Pipes[0]);
       SetCloseExec(Pipes[1],true);
-      
+
       // Purified Fork for running the script
-      pid_t Process = ExecFork();      
+      pid_t Process = ExecFork();
       if (Process == 0)
       {
 	 // Setup the FDs
-	 dup2(Pipes[0],STDIN_FILENO);
+	 dup2(Pipes[0], InfoFD);
 	 SetCloseExec(STDOUT_FILENO,false);
-	 SetCloseExec(STDIN_FILENO,false);      
+	 SetCloseExec(STDIN_FILENO,false);
 	 SetCloseExec(STDERR_FILENO,false);
 
+	 string hookfd;
+	 strprintf(hookfd, "%d", InfoFD);
+	 setenv("APT_HOOK_INFO_FD", hookfd.c_str(), 1);
+
 	 dpkgChrootDirectory();
 	 const char *Args[4];
 	 Args[0] = "/bin/sh";
@@ -409,6 +417,8 @@ bool pkgDPkgPM::RunScriptsWithPkgs(const char *Cnf)
 	 execv(Args[0],(char **)Args);
 	 _exit(100);
       }
+      if (InfoFD == (unsigned)Pipes[0])
+	 _config->Clear("APT::Keep-Fds", Pipes[0]);
       close(Pipes[0]);
       FILE *F = fdopen(Pipes[1],"w");
       if (F == 0)
diff --git a/doc/apt.conf.5.xml b/doc/apt.conf.5.xml
index f5e1f966d..42119baa5 100644
--- a/doc/apt.conf.5.xml
+++ b/doc/apt.conf.5.xml
@@ -688,7 +688,8 @@ DPkg::Pre-Install-Pkgs {"/usr/sbin/dpkg-preconfigure --apt";};
      <literal>options</literal> this must be specified in list notation. The commands
      are invoked in order using <filename>/bin/sh</filename>; should any fail APT 
      will abort. APT will pass the filenames of all .deb files it is going to
-     install to the commands, one per line on standard input.</para>
+     install to the commands, one per line on the requested file descriptor, defaulting
+     to standard input.</para>
 
      <para>Version 2 of this protocol dumps more information, including the
      protocol version, the APT configuration space and the packages, files
@@ -700,7 +701,15 @@ DPkg::Pre-Install-Pkgs {"/usr/sbin/dpkg-preconfigure --apt";};
      <literal>DPkg::Tools::options::<replaceable>cmd</replaceable>::Version</literal>
      accordingly, the default being version 1. If APT isn't supporting the requested
      version it will send the information in the highest version it has support for instead.
-     </para></listitem>
+     </para>
+
+     <para>The file descriptor to be used to send the information can be requested with
+     <literal>DPkg::Tools::options::<replaceable>cmd</replaceable>::InfoFD</literal>
+     which defaults to <literal>0</literal> for standard input and is available since
+     version 0.9.11. Support for the option can be detected by looking for the environment
+     variable <envar>APT_HOOK_INFO_FD</envar> which contains the number of the used
+     file descriptor as a confirmation.</para>
+     </listitem>
      </varlistentry>
 
      <varlistentry><term><option>Run-Directory</option></term>
diff --git a/test/integration/test-bug-712116-dpkg-pre-install-pkgs-hook-multiarch b/test/integration/test-bug-712116-dpkg-pre-install-pkgs-hook-multiarch
index af65397ea..62355a6b5 100755
--- a/test/integration/test-bug-712116-dpkg-pre-install-pkgs-hook-multiarch
+++ b/test/integration/test-bug-712116-dpkg-pre-install-pkgs-hook-multiarch
@@ -26,95 +26,111 @@ hook='pre-install-pkgs'
 
 enablehookversion() {
 	echo "#!/bin/sh
-while read line; do
+FD=0
+echo -n > ${hook}-v${1}.list
+if [ -n \"${2}\" ]; then
+	FD=\$APT_HOOK_INFO_FD
+	if [ "\$FD" != \"${2}\" ]; then echo \"ERROR: Information is not on requested FD: \$FD != ${2}\" >> ${hook}-v${1}.list; fi
+fi
+while read </proc/\$\$/fd/\$FD line; do
 	if echo \"\$line\" | grep -Fq '**'; then
 		echo \"\$line\"
 	fi
-done > ${hook}-v${1}.list" > ${hook}-v${1}.sh
+done >> ${hook}-v${1}.list" > ${hook}-v${1}.sh
 	chmod +x ${hook}-v${1}.sh
 	echo "dpkg::${hook}:: \"./${hook}-v${1}.sh --foo -bar\";
 DPkg::Tools::options::\"./${hook}-v${1}.sh\"::Version \"$1\";" > rootdir/etc/apt/apt.conf.d/hook-v$1
+	if [ -n "$2" ]; then
+		echo "DPkg::Tools::options::\"./${hook}-v${1}.sh\"::InfoFD \"${2}\";" >> rootdir/etc/apt/apt.conf.d/hook-v$1
+	fi
 }
 
-enablehookversion 2
-enablehookversion 3
-
 observehook() {
 	rm -f ${hook}-v2.list ${hook}-v3.list
 	msgtest 'Observe hooks while' "$*"
 	testsuccess --nomsg aptget "$@" -y --force-yes
 }
 
-observehook install stuff -t stable
-testfileequal "${hook}-v2.list" 'libsame - < 1 **CONFIGURE**
+testrun() {
+	observehook install stuff -t stable
+	testfileequal "${hook}-v2.list" 'libsame - < 1 **CONFIGURE**
 toolkit - < 1 **CONFIGURE**
 stuff - < 1 **CONFIGURE**'
-testfileequal "${hook}-v3.list" 'libsame - - none < 1 amd64 same **CONFIGURE**
+	testfileequal "${hook}-v3.list" 'libsame - - none < 1 amd64 same **CONFIGURE**
 toolkit - - none < 1 all foreign **CONFIGURE**
 stuff - - none < 1 amd64 none **CONFIGURE**'
 
-observehook install stuff -t unstable
-testfileequal "${hook}-v2.list" 'libsame 1 < 2 **CONFIGURE**
+	observehook install stuff -t unstable
+	testfileequal "${hook}-v2.list" 'libsame 1 < 2 **CONFIGURE**
 toolkit 1 < 2 **CONFIGURE**
 stuff 1 < 2 **CONFIGURE**'
-testfileequal "${hook}-v3.list" 'libsame 1 amd64 same < 2 amd64 same **CONFIGURE**
+	testfileequal "${hook}-v3.list" 'libsame 1 amd64 same < 2 amd64 same **CONFIGURE**
 toolkit 1 all foreign < 2 amd64 foreign **CONFIGURE**
 stuff 1 amd64 none < 2 amd64 none **CONFIGURE**'
 
-observehook install stuff:i386 -t unstable
-testfileequal "${hook}-v2.list" 'stuff 2 > - **REMOVE**
+	observehook install stuff:i386 -t unstable
+	testfileequal "${hook}-v2.list" 'stuff 2 > - **REMOVE**
 libsame - < 2 **CONFIGURE**
 stuff - < 2 **CONFIGURE**'
-testfileequal "${hook}-v3.list" 'stuff 2 amd64 none > - - none **REMOVE**
+	testfileequal "${hook}-v3.list" 'stuff 2 amd64 none > - - none **REMOVE**
 libsame - - none < 2 i386 same **CONFIGURE**
 stuff - - none < 2 i386 none **CONFIGURE**'
 
-observehook remove libsame
-testfileequal "${hook}-v2.list" 'libsame 2 > - **REMOVE**'
-testfileequal "${hook}-v3.list" 'libsame 2 amd64 same > - - none **REMOVE**'
+	observehook remove libsame
+	testfileequal "${hook}-v2.list" 'libsame 2 > - **REMOVE**'
+	testfileequal "${hook}-v3.list" 'libsame 2 amd64 same > - - none **REMOVE**'
 
-observehook install stuff:i386/stable libsame:i386/stable toolkit/stable
-testfileequal "${hook}-v2.list" 'libsame 2 > 1 **CONFIGURE**
+	observehook install stuff:i386/stable libsame:i386/stable toolkit/stable
+	testfileequal "${hook}-v2.list" 'libsame 2 > 1 **CONFIGURE**
 toolkit 2 > 1 **CONFIGURE**
 stuff 2 > 1 **CONFIGURE**'
-testfileequal "${hook}-v3.list" 'libsame 2 i386 same > 1 i386 same **CONFIGURE**
+	testfileequal "${hook}-v3.list" 'libsame 2 i386 same > 1 i386 same **CONFIGURE**
 toolkit 2 amd64 foreign > 1 all foreign **CONFIGURE**
 stuff 2 i386 none > 1 i386 none **CONFIGURE**'
 
-observehook install 'libsame:*'
-testfileequal "${hook}-v2.list" 'libsame 1 < 2 **CONFIGURE**
+	observehook install 'libsame:*'
+	testfileequal "${hook}-v2.list" 'libsame 1 < 2 **CONFIGURE**
 libsame - < 2 **CONFIGURE**
 toolkit 1 < 2 **CONFIGURE**
 stuff 1 < 2 **CONFIGURE**'
-testfileequal "${hook}-v3.list" 'libsame 1 i386 same < 2 i386 same **CONFIGURE**
+	testfileequal "${hook}-v3.list" 'libsame 1 i386 same < 2 i386 same **CONFIGURE**
 libsame - - none < 2 amd64 same **CONFIGURE**
 toolkit 1 all foreign < 2 amd64 foreign **CONFIGURE**
 stuff 1 i386 none < 2 i386 none **CONFIGURE**'
 
-observehook purge stuff:i386 'libsame:*' toolkit
-testfileequal "${hook}-v2.list" 'libsame 2 > - **REMOVE**
+	observehook purge stuff:i386 'libsame:*' toolkit
+	testfileequal "${hook}-v2.list" 'libsame 2 > - **REMOVE**
 stuff 2 > - **REMOVE**
 libsame 2 > - **REMOVE**
 toolkit 2 > - **REMOVE**'
-testfileequal "${hook}-v3.list" 'libsame 2 amd64 same > - - none **REMOVE**
+	testfileequal "${hook}-v3.list" 'libsame 2 amd64 same > - - none **REMOVE**
 stuff 2 i386 none > - - none **REMOVE**
 libsame 2 i386 same > - - none **REMOVE**
 toolkit 2 amd64 foreign > - - none **REMOVE**'
 
-observehook install confpkg
-testfileequal "${hook}-v2.list" 'confpkg - < 1 **CONFIGURE**'
-testfileequal "${hook}-v3.list" 'confpkg - - none < 1 amd64 none **CONFIGURE**'
+	observehook install confpkg
+	testfileequal "${hook}-v2.list" 'confpkg - < 1 **CONFIGURE**'
+	testfileequal "${hook}-v3.list" 'confpkg - - none < 1 amd64 none **CONFIGURE**'
+
+	observehook remove confpkg
+	testfileequal "${hook}-v2.list" 'confpkg 1 > - **REMOVE**'
+	testfileequal "${hook}-v3.list" 'confpkg 1 amd64 none > - - none **REMOVE**'
 
-observehook remove confpkg
-testfileequal "${hook}-v2.list" 'confpkg 1 > - **REMOVE**'
-testfileequal "${hook}-v3.list" 'confpkg 1 amd64 none > - - none **REMOVE**'
+	msgtest 'Conffiles of package remained after remove' 'confpkg'
+	dpkg -l confpkg | grep -q '^rc' && msgpass || msgfail
 
-msgtest 'Conffiles of package remained after remove' 'confpkg'
-dpkg -l confpkg | grep -q '^rc' && msgpass || msgfail
+	observehook purge confpkg
+	testfileequal "${hook}-v2.list" 'confpkg 1 > - **REMOVE**'
+	testfileequal "${hook}-v3.list" 'confpkg 1 amd64 none > - - none **REMOVE**'
 
-observehook purge confpkg
-testfileequal "${hook}-v2.list" 'confpkg 1 > - **REMOVE**'
-testfileequal "${hook}-v3.list" 'confpkg 1 amd64 none > - - none **REMOVE**'
+	msgtest 'Conffiles are gone after purge' 'confpkg'
+	dpkg -l confpkg 2>/dev/null | grep -q '^rc' && msgfail || msgpass
+}
+
+enablehookversion 2
+enablehookversion 3
+testrun
 
-msgtest 'Conffiles are gone after purge' 'confpkg'
-dpkg -l confpkg 2>/dev/null | grep -q '^rc' && msgfail || msgpass
+enablehookversion 2 13
+enablehookversion 3 13
+testrun