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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 /gnu/packages/aux-files
parent95460da83b6ffd2bf3b96b3ab7cd302ab76be38a (diff)
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.
Diffstat (limited to 'gnu/packages/aux-files')
-rw-r--r--gnu/packages/aux-files/run-in-namespace.c52
1 files changed, 44 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))