From 0cf7b1d928acaaddd4eaa28c6a22f7bd6457b379 Mon Sep 17 00:00:00 2001
From: Bernhard Voelker <mail@bernhard-voelker.de>
Date: Fri, 01 Aug 2014 00:07:33 +0000
Subject: chroot: perform chdir("/") again unless new --skip-chdir is specified
Since commit v8.22-94-g99960ee, chroot(1) skips the chroot(2) syscall
for "/" arguments (and synonyms). The problem is that it also skips
the following chdir("/") call in that case. The latter breaks existing
scripts which expect "/" to be the working directory inside the chroot.
While the first part of the change - i.e., skipping chroot("/") - is
okay for consistency with systems where it might succeed for a non-root
user, the second part might be malicious, e.g.
cd /home/user && chroot '/' bin/foo
In the "best" case, chroot(1) could not execute 'bin/foo' with ENOENT,
but in the worst case, chroot(1) would execute '/home/user/bin/foo' in
the case that exists - instead of '/bin/foo'.
Revert that second part of the patch, i.e., perform the chdir("/)
in the common case again - unless the new --skip-chdir option is
specified. Restrict this new option to the case of "/" arguments.
* src/chroot.c (SKIP_CHDIR): Add enum.
(long_opts): Add entry for the new --skip-chdir option.
(usage): Add --skip-chdir option, and while at it, move the other
to options into alphabetical order.
(main): Accept the above new option, allowing it only in the case
when NEWROOT is the old "/".
Move down the chdir() call after the if-clause to ensure it is
run in any case - unless --skip-chdir is specified.
Add a 'newroot' variable for the new root directory as it is used
in a couple of places now.
* tests/misc/chroot-fail.sh: Invert the last tests which check the
working directory of the execvp()ed program when a "/"-like
argument was passed: now expect it to be "/" - unless --skip-chdir
is given.
* doc/coreutils.texi (chroot invocation): Document the new option.
Document that chroot(1) usually calls chdir("/") unless the new
--skip-chdir option is specified. Sort options.
* init.cfg (nonroot_has_perm_): Add chroot's new --skip-chdir option.
* tests/cp/preserve-gid.sh (t1): Likewise.
* tests/cp/special-bits.sh: Likewise.
* tests/id/setgid.sh: Likewise.
* tests/misc/truncate-owned-by-other.sh: Likewise.
* tests/mv/sticky-to-xpart.sh: Likewise.
* tests/rm/fail-2eperm.sh: Likewise.
* tests/rm/no-give-up.sh: Likewise.
* tests/touch/now-owned-by-other.sh: Likewise.
Reported by Andreas Schwab in http://bugs.gnu.org/18062
---
diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 96f0781..7c86719 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -16113,7 +16113,10 @@ On many systems, only the super-user can do this.@footnote{However,
some systems (e.g., FreeBSD) can be configured to allow certain regular
users to use the @code{chroot} system call, and hence to run this program.
Also, on Cygwin, anyone can run the @command{chroot} command, because the
-underlying function is non-privileged due to lack of support in MS-Windows.}
+underlying function is non-privileged due to lack of support in MS-Windows.
+Furthermore, the @command{chroot} command avoids the @code{chroot} system call
+when @var{newroot} is identical to the old @file{/} directory for consistency
+with systems where this is allowed for non-privileged users.}.
Synopses:
@example
@@ -16123,10 +16126,11 @@ chroot @var{option}
Ordinarily, file names are looked up starting at the root of the
directory structure, i.e., @file{/}. @command{chroot} changes the root to
-the directory @var{newroot} (which must exist) and then runs
-@var{command} with optional @var{args}. If @var{command} is not
-specified, the default is the value of the @env{SHELL} environment
-variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
+the directory @var{newroot} (which must exist), then changes the working
+directory to @file{/}, and finally runs @var{command} with optional @var{args}.
+If @var{command} is not specified, the default is the value of the @env{SHELL}
+environment variable or @command{/bin/sh} if not set, invoked with the
+@option{-i} option.
@var{command} must not be a special built-in utility
(@pxref{Special built-in utilities}).
@@ -16135,6 +16139,14 @@ Options must precede operands.
@table @samp
+@item --groups=@var{groups}
+@opindex --groups
+Use this option to override the supplementary @var{groups} to be
+used by the new process.
+The items in the list (names or numeric IDs) must be separated by commas.
+Use @samp{--groups=''} to disable the supplementary group look-up
+implicit in the @option{--userspec} option.
+
@item --userspec=@var{user}[:@var{group}]
@opindex --userspec
By default, @var{command} is run with the same credentials
@@ -16145,13 +16157,13 @@ If a @var{user} is specified then the supplementary groups
are set according to the system defined list for that user,
unless overridden with the @option{--groups} option.
-@item --groups=@var{groups}
-@opindex --groups
-Use this option to override the supplementary @var{groups} to be
-used by the new process.
-The items in the list (names or numeric IDs) must be separated by commas.
-Use @samp{--groups=''} to disable the supplementary group look-up
-implicit in the @option{--userspec} option.
+@item --skip-chdir
+@opindex --skip-chdir
+Use this option to not change the working directory to @file{/} after changing
+the root directory to @var{newroot}, i.e., inside the chroot.
+This option is only permitted when @var{newroot} is the old @file{/} directory,
+and therefore is mostly useful together with the @option{--groups} and
+@option{--userspec} options to retain the previous working directory.
@end table
diff --git a/init.cfg b/init.cfg
index 725ee12..032646b 100644
--- a/init.cfg
+++ b/init.cfg
@@ -400,7 +400,8 @@ nonroot_has_perm_()
require_built_ chroot
local rm_version=$(
- chroot --user=$NON_ROOT_USERNAME / env PATH="$PATH" rm --version |
+ chroot --skip-chdir --user=$NON_ROOT_USERNAME / env PATH="$PATH" \
+ rm --version |
sed -n '1s/.* //p'
)
case ":$rm_version:" in
diff --git a/src/chroot.c b/src/chroot.c
index 6c2d63f..418ea67 100644
--- a/src/chroot.c
+++ b/src/chroot.c
@@ -49,13 +49,15 @@ static inline bool gid_unset (gid_t gid) { return gid == (gid_t) -1; }
enum
{
GROUPS = UCHAR_MAX + 1,
- USERSPEC
+ USERSPEC,
+ SKIP_CHDIR
};
static struct option const long_opts[] =
{
{"groups", required_argument, NULL, GROUPS},
{"userspec", required_argument, NULL, USERSPEC},
+ {"skip-chdir", no_argument, NULL, SKIP_CHDIR},
{GETOPT_HELP_OPTION_DECL},
{GETOPT_VERSION_OPTION_DECL},
{NULL, 0, NULL, 0}
@@ -194,9 +196,14 @@ Run COMMAND with root directory set to NEWROOT.\n\
"), stdout);
fputs (_("\
- --userspec=USER:GROUP specify user and group (ID or name) to use\n\
--groups=G_LIST specify supplementary groups as g1,g2,..,gN\n\
"), stdout);
+ fputs (_("\
+ --userspec=USER:GROUP specify user and group (ID or name) to use\n\
+"), stdout);
+ printf (_("\
+ --skip-chdir do not change working directory to %s\n\
+"), quote ("/"));
fputs (HELP_OPTION_DESCRIPTION, stdout);
fputs (VERSION_OPTION_DESCRIPTION, stdout);
@@ -218,6 +225,7 @@ main (int argc, char **argv)
char *userspec = NULL;
char const *username = NULL;
char const *groups = NULL;
+ bool skip_chdir = false;
/* Parsed user and group IDs. */
uid_t uid = -1;
@@ -254,6 +262,10 @@ main (int argc, char **argv)
groups = optarg;
break;
+ case SKIP_CHDIR:
+ skip_chdir = true;
+ break;
+
case_GETOPT_HELP_CHAR;
case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
@@ -269,9 +281,19 @@ main (int argc, char **argv)
usage (EXIT_CANCELED);
}
+ char const *newroot = argv[optind];
+ bool is_oldroot = is_root (newroot);
+
+ if (! is_oldroot && skip_chdir)
+ {
+ error (0, 0, _("option --skip-chdir only permitted if NEWROOT is old %s"),
+ quote ("/"));
+ usage (EXIT_CANCELED);
+ }
+
/* Only do chroot specific actions if actually changing root.
The main difference here is that we don't change working dir. */
- if (! is_root (argv[optind]))
+ if (! is_oldroot)
{
/* We have to look up users and groups twice.
- First, outside the chroot to load potentially necessary passwd/group
@@ -307,14 +329,14 @@ main (int argc, char **argv)
}
#endif
- if (chroot (argv[optind]) != 0)
+ if (chroot (newroot) != 0)
error (EXIT_CANCELED, errno, _("cannot change root directory to %s"),
- argv[optind]);
-
- if (chdir ("/"))
- error (EXIT_CANCELED, errno, _("cannot chdir to root directory"));
+ newroot);
}
+ if (! skip_chdir && chdir ("/"))
+ error (EXIT_CANCELED, errno, _("cannot chdir to root directory"));
+
if (argc == optind + 1)
{
/* No command. Run an interactive shell. */
diff --git a/tests/cp/preserve-gid.sh b/tests/cp/preserve-gid.sh
index f141ac1..5499c2e 100755
--- a/tests/cp/preserve-gid.sh
+++ b/tests/cp/preserve-gid.sh
@@ -117,7 +117,8 @@ t1() {
u=$1; shift
g=$1; shift
t0 "$f" "$u" "$g" \
- chroot --user=+$nameless_uid:+$nameless_gid1 \
+ chroot --skip-chdir \
+ --user=+$nameless_uid:+$nameless_gid1 \
--groups="+$nameless_gid1,+$nameless_gid2" \
/ env PATH="$tmp_path" "$@"
}
diff --git a/tests/cp/special-bits.sh b/tests/cp/special-bits.sh
index a55eea2..1402819 100755
--- a/tests/cp/special-bits.sh
+++ b/tests/cp/special-bits.sh
@@ -42,7 +42,8 @@ set _ $(ls -l b); shift; p1=$1
set _ $(ls -l b2); shift; p2=$1
test $p1 = $p2 || fail=1
-chroot --user=$NON_ROOT_USERNAME / env PATH="$PATH" cp -p c c2 || fail=1
+chroot --skip-chdir --user=$NON_ROOT_USERNAME / env PATH="$PATH" cp -p c c2 \
+ || fail=1
set _ $(ls -l c); shift; p1=$1
set _ $(ls -l c2); shift; p2=$1
test $p1 = $p2 && fail=1
diff --git a/tests/id/setgid.sh b/tests/id/setgid.sh
index 6d9d74f..019418a 100755
--- a/tests/id/setgid.sh
+++ b/tests/id/setgid.sh
@@ -27,14 +27,14 @@ echo $gp1 > exp || framework_failure_
# With coreutils-8.16 and earlier, id -G would print both:
# $gp1 $NON_ROOT_GID
-chroot --user=$NON_ROOT_USERNAME:+$gp1 --groups='' / env PATH="$PATH" \
- id -G > out || fail=1
+chroot --skip-chdir --user=$NON_ROOT_USERNAME:+$gp1 --groups='' / \
+ env PATH="$PATH" id -G > out || fail=1
compare exp out || fail=1
# With coreutils-8.22 and earlier, id would erroneously print
# groups=$NON_ROOT_GID
-chroot --user=$NON_ROOT_USERNAME:+$gp1 --groups='' / env PATH="$PATH" \
- id > out || fail=1
+chroot --skip-chdir --user=$NON_ROOT_USERNAME:+$gp1 --groups='' / \
+ env PATH="$PATH" id > out || fail=1
grep -F "groups=$gp1" out || { cat out; fail=1; }
Exit $fail
diff --git a/tests/misc/chroot-fail.sh b/tests/misc/chroot-fail.sh
index a84826f..82ae23c 100755
--- a/tests/misc/chroot-fail.sh
+++ b/tests/misc/chroot-fail.sh
@@ -30,7 +30,7 @@ chroot --- / true # unknown option
test $? = 125 || fail=1
# Note chroot("/") succeeds for non-root users on some systems, but not all,
-# however we avoid the chroot() with "/" to have common behvavior.
+# however we avoid the chroot() with "/" to have common behavior.
chroot / sh -c 'exit 2' # exit status propagation
test $? = 2 || fail=1
chroot / . # invalid command
@@ -38,10 +38,25 @@ test $? = 126 || fail=1
chroot / no_such # no such command
test $? = 127 || fail=1
-# Ensure we don't chdir("/") when not changing root
-# to allow only changing user ids for a command.
-for dir in '/' '/.' '/../'; do
+# Ensure that --skip-chdir fails with a non-"/" argument.
+cat <<\EOF > exp || framework_failure_
+chroot: option --skip-chdir only permitted if NEWROOT is old '/'
+Try 'chroot --help' for more information.
+EOF
+chroot --skip-chdir . env pwd >out 2>err && fail=1
+compare /dev/null out || fail=1
+compare exp err || fail=1
+
+# Ensure we don't chroot("/") when NEWROOT is old "/".
+ln -s / isroot || framework_failure_
+for dir in '/' '/.' '/../' isroot; do
+ # Verify that chroot(1) succeeds and performs chdir("/")
+ # (chroot(1) of coreutils-8.23 failed to run the latter).
curdir=$(chroot "$dir" env pwd) || fail=1
+ test "$curdir" = '/' || fail=1
+
+ # Test the "--skip-chdir" option.
+ curdir=$(chroot --skip-chdir "$dir" env pwd) || fail=1
test "$curdir" = '/' && fail=1
done
diff --git a/tests/misc/truncate-owned-by-other.sh b/tests/misc/truncate-owned-by-other.sh
index e70badb..f65439e 100755
--- a/tests/misc/truncate-owned-by-other.sh
+++ b/tests/misc/truncate-owned-by-other.sh
@@ -29,7 +29,7 @@ chmod g+w root-owned
# Ensure that the current directory is searchable by $NON_ROOT_USERNAME.
chmod g+x .
-chroot --user=$NON_ROOT_USERNAME / env PATH="$PATH" \
+chroot --skip-chdir --user=$NON_ROOT_USERNAME / env PATH="$PATH" \
truncate -s0 root-owned || fail=1
Exit $fail
diff --git a/tests/mv/sticky-to-xpart.sh b/tests/mv/sticky-to-xpart.sh
index e0c99e9..6c1f6e8 100755
--- a/tests/mv/sticky-to-xpart.sh
+++ b/tests/mv/sticky-to-xpart.sh
@@ -42,7 +42,8 @@ chmod go+x . || framework_failure_
# Ensure that $NON_ROOT_USERNAME can access the required version of mv.
version=$(
- chroot --user=$NON_ROOT_USERNAME / env PATH="$PATH" mv --version |
+ chroot --skip-chdir --user=$NON_ROOT_USERNAME / env PATH="$PATH" \
+ mv --version |
sed -n '1s/.* //p'
)
case $version in
@@ -50,7 +51,7 @@ case $version in
*) skip_ "cannot access just-built mv as user $NON_ROOT_USERNAME";;
esac
-chroot --user=$NON_ROOT_USERNAME / env PATH="$PATH" \
+chroot --skip-chdir --user=$NON_ROOT_USERNAME / env PATH="$PATH" \
mv t/root-owned "$other_partition_tmpdir" 2> out-t && fail=1
# On some systems, we get 'Not owner'. Convert it.
diff --git a/tests/rm/fail-2eperm.sh b/tests/rm/fail-2eperm.sh
index 6e8ce9b..c324037 100755
--- a/tests/rm/fail-2eperm.sh
+++ b/tests/rm/fail-2eperm.sh
@@ -32,14 +32,16 @@ touch a/b || framework_failure_
# Try to ensure that $NON_ROOT_USERNAME can access
# the required version of rm.
rm_version=$(
- chroot --user=$NON_ROOT_USERNAME / env PATH="$PATH" rm --version |
+ chroot --skip-chdir --user=$NON_ROOT_USERNAME / env PATH="$PATH" \
+ rm --version |
sed -n '1s/.* //p'
)
case $rm_version in
$PACKAGE_VERSION) ;;
*) skip_ "cannot access just-built rm as user $NON_ROOT_USERNAME";;
esac
-chroot --user=$NON_ROOT_USERNAME / env PATH="$PATH" rm -rf a 2> out-t && fail=1
+chroot --skip-chdir --user=$NON_ROOT_USERNAME / \
+ env PATH="$PATH" rm -rf a 2> out-t && fail=1
# On some systems, we get 'Not owner'. Convert it.
# On other systems (HPUX), we get 'Permission denied'. Convert it, too.
diff --git a/tests/rm/no-give-up.sh b/tests/rm/no-give-up.sh
index 41070c9..958f9e8 100755
--- a/tests/rm/no-give-up.sh
+++ b/tests/rm/no-give-up.sh
@@ -30,7 +30,7 @@ chmod go=x . || framework_failure_
# This must fail, since '.' is not writable by $NON_ROOT_USERNAME.
-chroot --user=$NON_ROOT_USERNAME / env PATH="$PATH" \
+chroot --skip-chdir --user=$NON_ROOT_USERNAME / env PATH="$PATH" \
rm -rf d 2>/dev/null && fail=1
# d must remain.
diff --git a/tests/touch/now-owned-by-other.sh b/tests/touch/now-owned-by-other.sh
index d01097e..018ef11 100755
--- a/tests/touch/now-owned-by-other.sh
+++ b/tests/touch/now-owned-by-other.sh
@@ -28,7 +28,7 @@ chmod g+w root-owned
# Ensure that the current directory is searchable by $NON_ROOT_USERNAME.
chmod g+x .
-chroot --user=$NON_ROOT_USERNAME / env PATH="$PATH" \
+chroot --skip-chdir --user=$NON_ROOT_USERNAME / env PATH="$PATH" \
touch -d now root-owned || fail=1
Exit $fail
--
cgit v0.9.0.2