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pack: Add relocation via ld.so and fakechroot.

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* gnu/packages/aux-files/run-in-namespace.c (HAVE_EXEC_WITH_LOADER): New
macro.
(bind_mount): Rename to...
(mirror_directory): ... this.  Add 'firmlink' argument and use it
instead of calling mkdir/open/close/mount directly.
(bind_mount, make_symlink): New functions.
(exec_in_user_namespace): Adjust accordingly.
(exec_with_loader) [HAVE_EXEC_WITH_LOADER]: New function.
(exec_performance): New function.
(engines): Add them.
* guix/scripts/pack.scm (wrapped-package)[fakechroot-library]
[audit-module]: New procedures.
[audit-source]: New variable.
[build](elf-interpreter, elf-loader-compile-flags): New procedures.
(build-wrapper): Use them.
* tests/guix-pack-relocatable.sh: Test with
'GUIX_EXECUTION_ENGINE=fakechroot'.
* doc/guix.texi (Invoking guix pack): Document the 'performance' and
'fakechroot' engines.
* gnu/packages/aux-files/pack-audit.c: New file.
* Makefile.am (AUX_FILES): Add it.
This commit is contained in:
Ludovic Courtès 2020-05-07 22:49:20 +02:00 committed by Ludovic Courtès
parent 4449e7c5e4
commit 6456232164
No known key found for this signature in database
GPG Key ID: 090B11993D9AEBB5
6 changed files with 331 additions and 21 deletions
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1
Makefile.am
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@ -338,6 +338,7 @@ AUX_FILES = \
gnu/packages/aux-files/linux-libre/4.9-x86_64.conf \
gnu/packages/aux-files/linux-libre/4.4-i686.conf \
gnu/packages/aux-files/linux-libre/4.4-x86_64.conf \
gnu/packages/aux-files/pack-audit.c \
gnu/packages/aux-files/run-in-namespace.c
# Templates, examples.

13
doc/guix.texi
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@ -5230,6 +5230,10 @@ following execution engines are supported:
Try user namespaces and fall back to PRoot if user namespaces are not
supported (see below).
@item performance
Try user namespaces and fall back to Fakechroot if user namespaces are
not supported (see below).
@item userns
Run the program through user namespaces and abort if they are not
supported.
@ -5241,6 +5245,15 @@ support for file system virtualization. It achieves that by using the
@code{ptrace} system call on the running program. This approach has the
advantage to work without requiring special kernel support, but it incurs
run-time overhead every time a system call is made.
@item fakechroot
Run through Fakechroot. @uref{https://github.com/dex4er/fakechroot/,
Fakechroot} virtualizes file system accesses by intercepting calls to C
library functions such as @code{open}, @code{stat}, @code{exec}, and so
on. Unlike PRoot, it incurs very little overhead. However, it does not
always work: for example, some file system accesses made from within the
C library are not intercepted, and file system accesses made @i{via}
direct syscalls are not intercepted either, leading to erratic behavior.
@end table
@vindex GUIX_EXECUTION_ENGINE

85
gnu/packages/aux-files/pack-audit.c Normal file
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@ -0,0 +1,85 @@
/* GNU Guix --- Functional package management for GNU
Copyright (C) 2020 Ludovic Courtès <ludo@gnu.org>
This file is part of GNU Guix.
GNU Guix is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or (at
your option) any later version.
GNU Guix is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with GNU Guix. If not, see <http://www.gnu.org/licenses/>. */
/* This file implements part of the GNU ld.so audit interface. It is used by
the "fakechroot" engine of the 'guix pack -RR' wrappers to make sure the
loader looks for shared objects under the "fake" root directory. */
#define _GNU_SOURCE 1
#include <link.h>
#include <error.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
/* The pseudo root directory and store that we are relocating to. */
static const char *root_directory;
static char *store;
/* The original store, "/gnu/store" by default. */
static const char original_store[] = "@STORE_DIRECTORY@";
/* Like 'malloc', but abort if 'malloc' returns NULL. */
static void *
xmalloc (size_t size)
{
void *result = malloc (size);
assert (result != NULL);
return result;
}
unsigned int
la_version (unsigned int v)
{
if (v != LAV_CURRENT)
error (1, 0, "cannot handle interface version %u", v);
root_directory = getenv ("FAKECHROOT_BASE");
if (root_directory == NULL)
error (1, 0, "'FAKECHROOT_BASE' is not set");
store = xmalloc (strlen (root_directory) + sizeof original_store);
strcpy (store, root_directory);
strcat (store, original_store);
return v;
}
/* Return NAME, a shared object file name, relocated under STORE. This
function is called by the loader whenever it looks for a shared object. */
char *
la_objsearch (const char *name, uintptr_t *cookie, unsigned int flag)
{
char *result;
if (strncmp (name, original_store,
sizeof original_store - 1) == 0)
{
size_t len = strlen (name) - sizeof original_store
+ strlen (store) + 1;
result = xmalloc (len);
strcpy (result, store);
strcat (result, name + sizeof original_store - 1);
}
else
result = strdup (name);
return result;
}

160
gnu/packages/aux-files/run-in-namespace.c
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@ -42,6 +42,11 @@
#include <dirent.h>
#include <sys/syscall.h>
/* Whether we're building the ld.so/libfakechroot wrapper. */
#define HAVE_EXEC_WITH_LOADER \
(defined PROGRAM_INTERPRETER) && (defined LOADER_AUDIT_MODULE) \
&& (defined FAKECHROOT_LIBRARY)
/* The original store, "/gnu/store" by default. */
static const char original_store[] = "@STORE_DIRECTORY@";
@ -117,9 +122,42 @@ rm_rf (const char *directory)
assert_perror (errno);
}
/* Bind mount all the top-level entries in SOURCE to TARGET. */
/* Make TARGET a bind-mount of SOURCE. Take into account ENTRY's type, which
corresponds to SOURCE. */
static int
bind_mount (const char *source, const struct dirent *entry,
const char *target)
{
if (entry->d_type == DT_DIR)
{
int err = mkdir (target, 0700);
if (err != 0)
return err;
}
else
close (open (target, O_WRONLY | O_CREAT));
return mount (source, target, "none",
MS_BIND | MS_REC | MS_RDONLY, NULL);
}
#if HAVE_EXEC_WITH_LOADER
/* Make TARGET a symlink to SOURCE. */
static int
make_symlink (const char *source, const struct dirent *entry,
const char *target)
{
return symlink (source, target);
}
#endif
/* Mirror with FIRMLINK all the top-level entries in SOURCE to TARGET. */
static void
bind_mount (const char *source, const char *target)
mirror_directory (const char *source, const char *target,
int (* firmlink) (const char *, const struct dirent *,
const char *))
{
DIR *stream = opendir (source);
@ -154,17 +192,7 @@ bind_mount (const char *source, const char *target)
else
{
/* Create the mount point. */
if (entry->d_type == DT_DIR)
{
int err = mkdir (new_entry, 0700);
if (err != 0)
assert_perror (errno);
}
else
close (open (new_entry, O_WRONLY | O_CREAT));
int err = mount (abs_source, new_entry, "none",
MS_BIND | MS_REC | MS_RDONLY, NULL);
int err = firmlink (abs_source, entry, new_entry);
/* It used to be that only directories could be bind-mounted. Thus,
keep going if we fail to bind-mount a non-directory entry.
@ -248,7 +276,7 @@ exec_in_user_namespace (const char *store, int argc, char *argv[])
/* Note: Due to <https://bugzilla.kernel.org/show_bug.cgi?id=183461>
we cannot make NEW_ROOT a tmpfs (which would have saved the need
for 'rm_rf'.) */
bind_mount ("/", new_root);
mirror_directory ("/", new_root, bind_mount);
mkdir_p (new_store);
err = mount (store, new_store, "none", MS_BIND | MS_REC | MS_RDONLY,
NULL);
@ -340,6 +368,92 @@ exec_with_proot (const char *store, int argc, char *argv[])
#endif
#if HAVE_EXEC_WITH_LOADER
/* Execute the wrapped program by invoking the loader (ld.so) directly,
passing it the audit module and preloading libfakechroot.so. */
static void
exec_with_loader (const char *store, int argc, char *argv[])
{
char *loader = concat (store,
PROGRAM_INTERPRETER + sizeof original_store);
size_t loader_specific_argc = 6;
size_t loader_argc = argc + loader_specific_argc;
char *loader_argv[loader_argc + 1];
loader_argv[0] = argv[0];
loader_argv[1] = "--audit";
loader_argv[2] = concat (store,
LOADER_AUDIT_MODULE + sizeof original_store);
loader_argv[3] = "--preload";
loader_argv[4] = concat (store,
FAKECHROOT_LIBRARY + sizeof original_store);
loader_argv[5] = concat (store,
"@WRAPPED_PROGRAM@" + sizeof original_store);
for (size_t i = 0; i < argc; i++)
loader_argv[i + loader_specific_argc] = argv[i + 1];
loader_argv[loader_argc] = NULL;
/* Set up the root directory. */
int err;
char *new_root = mkdtemp (strdup ("/tmp/guix-exec-XXXXXX"));
mirror_directory ("/", new_root, make_symlink);
char *new_store = concat (new_root, original_store);
char *new_store_parent = dirname (strdup (new_store));
mkdir_p (new_store_parent);
symlink (store, new_store);
#ifdef GCONV_DIRECTORY
/* Tell libc where to find its gconv modules. This is necessary because
gconv uses non-interposable 'open' calls. */
char *gconv_path = concat (store,
GCONV_DIRECTORY + sizeof original_store);
setenv ("GCONV_PATH", gconv_path, 1);
free (gconv_path);
#endif
setenv ("FAKECHROOT_BASE", new_root, 1);
pid_t child = fork ();
switch (child)
{
case 0:
err = execv (loader, loader_argv);
if (err < 0)
assert_perror (errno);
exit (EXIT_FAILURE);
break;
case -1:
assert_perror (errno);
exit (EXIT_FAILURE);
break;
default:
{
int status;
waitpid (child, &status, 0);
chdir ("/"); /* avoid EBUSY */
rm_rf (new_root);
free (new_root);
close (2); /* flushing stderr should be silent */
if (WIFEXITED (status))
exit (WEXITSTATUS (status));
else
/* Abnormal termination cannot really be reproduced, so exit
with 255. */
exit (255);
}
}
}
#endif
/* Execution engines. */
@ -356,7 +470,7 @@ buffer_stderr (void)
setvbuf (stderr, stderr_buffer, _IOFBF, sizeof stderr_buffer);
}
/* The default engine. */
/* The default engine: choose a robust method. */
static void
exec_default (const char *store, int argc, char *argv[])
{
@ -370,13 +484,29 @@ exec_default (const char *store, int argc, char *argv[])
#endif
}
/* The "performance" engine: choose performance over robustness. */
static void
exec_performance (const char *store, int argc, char *argv[])
{
buffer_stderr ();
exec_in_user_namespace (store, argc, argv);
#if HAVE_EXEC_WITH_LOADER
exec_with_loader (store, argc, argv);
#endif
}
/* List of supported engines. */
static const struct engine engines[] =
{
{ "default", exec_default },
{ "performance", exec_performance },
{ "userns", exec_in_user_namespace },
#ifdef PROOT_PROGRAM
{ "proot", exec_with_proot },
#endif
#if HAVE_EXEC_WITH_LOADER
{ "fakechroot", exec_with_loader },
#endif
{ NULL, NULL }
};

83
guix/scripts/pack.scm
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@ -684,18 +684,50 @@ last resort for relocation."
(define runner
(local-file (search-auxiliary-file "run-in-namespace.c")))
(define audit-source
(local-file (search-auxiliary-file "pack-audit.c")))
(define (proot)
(specification->package "proot-static"))
(define (fakechroot-library)
(computed-file "libfakechroot.so"
#~(copy-file #$(file-append
(specification->package "fakechroot")
"/lib/fakechroot/libfakechroot.so")
#$output)))
(define (audit-module)
;; Return an ld.so audit module for use by the 'fakechroot' execution
;; engine that translates file names of all the files ld.so loads.
(computed-file "pack-audit.so"
(with-imported-modules '((guix build utils))
#~(begin
(use-modules (guix build utils))
(copy-file #$audit-source "audit.c")
(substitute* "audit.c"
(("@STORE_DIRECTORY@")
(%store-directory)))
(invoke #$compiler "-std=gnu99"
"-shared" "-fPIC" "-Os" "-g0"
"-Wall" "audit.c" "-o" #$output)))))
(define build
(with-imported-modules (source-module-closure
'((guix build utils)
(guix build union)))
(guix build union)
(guix elf)))
#~(begin
(use-modules (guix build utils)
((guix build union) #:select (relative-file-name))
(guix elf)
(ice-9 binary-ports)
(ice-9 ftw)
(ice-9 match))
(ice-9 match)
(srfi srfi-1)
(rnrs bytevectors))
(define input
;; The OUTPUT* output of PACKAGE.
@ -714,6 +746,48 @@ last resort for relocation."
(#f base)
(index (string-drop base index)))))
(define (elf-interpreter elf)
;; Return the interpreter of ELF as a string, or #f if ELF has no
;; interpreter segment.
(match (find (lambda (segment)
(= (elf-segment-type segment) PT_INTERP))
(elf-segments elf))
(#f #f) ;maybe a .so
(segment
(let ((bv (make-bytevector (- (elf-segment-memsz segment) 1))))
(bytevector-copy! (elf-bytes elf)
(elf-segment-offset segment)
bv 0 (bytevector-length bv))
(utf8->string bv)))))
(define (elf-loader-compile-flags program)
;; Return the cpp flags defining macros for the ld.so/fakechroot
;; wrapper of PROGRAM.
;; TODO: Handle scripts by wrapping their interpreter.
(if (elf-file? program)
(let* ((bv (call-with-input-file program
get-bytevector-all))
(elf (parse-elf bv))
(interp (elf-interpreter elf))
(gconv (and interp
(string-append (dirname interp)
"/gconv"))))
(if interp
(list (string-append "-DPROGRAM_INTERPRETER=\""
interp "\"")
(string-append "-DFAKECHROOT_LIBRARY=\""
#$(fakechroot-library) "\"")
(string-append "-DLOADER_AUDIT_MODULE=\""
#$(audit-module) "\"")
(if gconv
(string-append "-DGCONV_DIRECTORY=\""
gconv "\"")
"-UGCONV_DIRECTORY"))
'()))
'()))
(define (build-wrapper program)
;; Build a user-namespace wrapper for PROGRAM.
(format #t "building wrapper for '~a'...~%" program)
@ -733,10 +807,11 @@ last resort for relocation."
(mkdir-p (dirname result))
(apply invoke #$compiler "-std=gnu99" "-static" "-Os" "-g0" "-Wall"
"run.c" "-o" result
(if proot
(append (if proot
(list (string-append "-DPROOT_PROGRAM=\""
proot "\""))
'()))
'())
(elf-loader-compile-flags program)))
(delete-file "run.c")))
(setvbuf (current-output-port) 'line)

6
tests/guix-pack-relocatable.sh
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@ -94,6 +94,12 @@ case "`uname -m`" in
export GUIX_EXECUTION_ENGINE
"$test_directory/Bin/sed" --version > "$test_directory/output"
grep 'GNU sed' "$test_directory/output"
# Now with fakechroot.
GUIX_EXECUTION_ENGINE="fakechroot"
"$test_directory/Bin/sed" --version > "$test_directory/output"
grep 'GNU sed' "$test_directory/output"
chmod -Rf +w "$test_directory"; rm -rf "$test_directory"/*
;;
*)