aboutsummaryrefslogtreecommitdiff
diff options
context:
space:
mode:
authorLudovic Courtès <ludo@gnu.org>2020-10-31 23:02:33 +0100
committerLudovic Courtès <ludo@gnu.org>2020-10-31 23:16:43 +0100
commitbfe82fe2f6e9f34c0774fe2114cdc7e937ba8bd2 (patch)
tree5140552cb16dc6a5eb611054a2b44023e259fdf6
parent95460da83b6ffd2bf3b96b3ab7cd302ab76be38a (diff)
downloadguix-bfe82fe2f6e9f34c0774fe2114cdc7e937ba8bd2.tar.gz
guix-bfe82fe2f6e9f34c0774fe2114cdc7e937ba8bd2.zip
pack: Relocatable wrapper leaves root available to child processes.
Fixes <https://bugs.gnu.org/44261>. Reported by Jan Nieuwenhuizen <janneke@gnu.org>. * gnu/packages/aux-files/run-in-namespace.c (exec_in_user_namespace): Add call to 'prctl'. Call 'mount' for NEW_ROOT and define 'is_tmpfs'. When IS_TMPFS is true, call 'umount' and 'rmdir' after 'waitpid'; otherwise, call 'rm_rf' only when 'waitpid' returns -1 the second time. (exec_with_loader): Call 'prctl'. Remove NEW_ROOT only when 'waitpid' returns -1 the second time, otherwise leave it behind. * tests/guix-pack-relocatable.sh (wait_for_file): New function. Add test.
-rw-r--r--gnu/packages/aux-files/run-in-namespace.c52
-rw-r--r--tests/guix-pack-relocatable.sh73
2 files changed, 117 insertions, 8 deletions
diff --git a/gnu/packages/aux-files/run-in-namespace.c b/gnu/packages/aux-files/run-in-namespace.c
index 947ff02dda..44c3c5a6cb 100644
--- a/gnu/packages/aux-files/run-in-namespace.c
+++ b/gnu/packages/aux-files/run-in-namespace.c
@@ -41,6 +41,7 @@
#include <fcntl.h>
#include <dirent.h>
#include <sys/syscall.h>
+#include <sys/prctl.h>
/* Whether we're building the ld.so/libfakechroot wrapper. */
#define HAVE_EXEC_WITH_LOADER \
@@ -258,11 +259,20 @@ exec_in_user_namespace (const char *store, int argc, char *argv[])
{
/* Spawn @WRAPPED_PROGRAM@ in a separate namespace where STORE is
bind-mounted in the right place. */
- int err;
+ int err, is_tmpfs;
char *new_root = mkdtemp (strdup ("/tmp/guix-exec-XXXXXX"));
char *new_store = concat (new_root, original_store);
char *cwd = get_current_dir_name ();
+ /* Become the new parent of grand-children when their parent dies. */
+ prctl (PR_SET_CHILD_SUBREAPER, 1);
+
+ /* Optionally, make NEW_ROOT a tmpfs. That way, if we have to leave it
+ behind because there are sub-processes still running when this wrapper
+ exits, it's OK. */
+ err = mount ("none", new_root, "tmpfs", 0, NULL);
+ is_tmpfs = (err == 0);
+
/* Create a child with separate namespaces and set up bind-mounts from
there. That way, bind-mounts automatically disappear when the child
exits, which simplifies cleanup for the parent. Note: clone is more
@@ -300,6 +310,7 @@ exec_in_user_namespace (const char *store, int argc, char *argv[])
/* Failure: user namespaces not supported. */
fprintf (stderr, "%s: error: 'clone' failed: %m\n", argv[0]);
rm_rf (new_root);
+ free (new_root);
break;
default:
@@ -312,10 +323,25 @@ exec_in_user_namespace (const char *store, int argc, char *argv[])
write_id_map (child, "uid_map", getuid ());
write_id_map (child, "gid_map", getgid ());
- int status;
+ int status, status_other;
waitpid (child, &status, 0);
- chdir ("/"); /* avoid EBUSY */
- rm_rf (new_root);
+
+ chdir ("/"); /* avoid EBUSY */
+ if (is_tmpfs)
+ {
+ /* NEW_ROOT lives on in child processes and we no longer need it
+ to exist as an empty directory in the global namespace. */
+ umount (new_root);
+ rmdir (new_root);
+ }
+ /* Check whether there are child processes left. If there are none,
+ we can remove NEW_ROOT just fine. Conversely, if there are
+ processes left (for example because this wrapper's child forked),
+ we have to leave NEW_ROOT behind so that those processes can still
+ access their root file system (XXX). */
+ else if (waitpid (-1 , &status_other, WNOHANG) == -1)
+ rm_rf (new_root);
+
free (new_root);
if (WIFEXITED (status))
@@ -490,6 +516,9 @@ exec_with_loader (const char *store, int argc, char *argv[])
setenv ("FAKECHROOT_BASE", new_root, 1);
+ /* Become the new parent of grand-children when their parent dies. */
+ prctl (PR_SET_CHILD_SUBREAPER, 1);
+
pid_t child = fork ();
switch (child)
{
@@ -507,12 +536,19 @@ exec_with_loader (const char *store, int argc, char *argv[])
default:
{
- int status;
+ int status, status_other;
waitpid (child, &status, 0);
- chdir ("/"); /* avoid EBUSY */
- rm_rf (new_root);
- free (new_root);
+ /* If there are child processes still running, leave NEW_ROOT around
+ so they can still access it. XXX: In that case NEW_ROOT is left
+ behind. */
+ if (waitpid (-1 , &status_other, WNOHANG) == -1)
+ {
+ chdir ("/"); /* avoid EBUSY */
+ rm_rf (new_root);
+ }
+
+ free (new_root);
close (2); /* flushing stderr should be silent */
if (WIFEXITED (status))
diff --git a/tests/guix-pack-relocatable.sh b/tests/guix-pack-relocatable.sh
index eb04231d16..2beb1b1eb6 100644
--- a/tests/guix-pack-relocatable.sh
+++ b/tests/guix-pack-relocatable.sh
@@ -59,6 +59,19 @@ run_without_store ()
fi
}
+# Wait for the given file to show up. Error out if it doesn't show up in a
+# timely fashion.
+wait_for_file ()
+{
+ i=0
+ while ! test -f "$1" && test $i -lt 20
+ do
+ sleep 0.3
+ i=`expr $i + 1`
+ done
+ test -f "$1"
+}
+
test_directory="`mktemp -d`"
export test_directory
trap 'chmod -Rf +w "$test_directory"; rm -rf "$test_directory"' EXIT
@@ -131,6 +144,66 @@ case "`uname -m`" in
;;
esac
+if unshare -r true
+then
+ # Check what happens if the wrapped binary forks and leaves child
+ # processes behind, like a daemon. The root file system should remain
+ # available to those child processes. See <https://bugs.gnu.org/44261>.
+ cat > "$test_directory/manifest.scm" <<EOF
+(use-modules (guix))
+
+(define daemon
+ (program-file "daemon"
+ #~(begin
+ (use-modules (ice-9 match)
+ (ice-9 ftw))
+
+ (call-with-output-file "parent-store"
+ (lambda (port)
+ (write (scandir (ungexp (%store-prefix)))
+ port)))
+
+ (match (primitive-fork)
+ (0 (sigaction SIGHUP (const #t))
+ (call-with-output-file "pid"
+ (lambda (port)
+ (display (getpid) port)))
+ (pause)
+ (call-with-output-file "child-store"
+ (lambda (port)
+ (write (scandir (ungexp (%store-prefix)))
+ port))))
+ (_ #t)))))
+
+(define package
+ (computed-file "package"
+ #~(let ((out (ungexp output)))
+ (mkdir out)
+ (mkdir (string-append out "/bin"))
+ (symlink (ungexp daemon)
+ (string-append out "/bin/daemon")))))
+
+(manifest (list (manifest-entry
+ (name "daemon")
+ (version "0")
+ (item package))))
+EOF
+
+ tarball="$(guix pack -S /bin=bin -R -m "$test_directory/manifest.scm")"
+ (cd "$test_directory"; tar xf "$tarball")
+
+ # Run '/bin/daemon', which forks, then wait for the child, send it SIGHUP
+ # so that it dumps its view of the store, and make sure the child and
+ # parent both see the same store contents.
+ (cd "$test_directory"; run_without_store ./bin/daemon)
+ wait_for_file "$test_directory/pid"
+ kill -HUP $(cat "$test_directory/pid")
+ wait_for_file "$test_directory/child-store"
+ diff -u "$test_directory/parent-store" "$test_directory/child-store"
+
+ chmod -Rf +w "$test_directory"; rm -rf "$test_directory"/*
+fi
+
# Ensure '-R' works with outputs other than "out".
tarball="`guix pack -R -S /share=share groff:doc`"
(cd "$test_directory"; tar xf "$tarball")