From 0cf7b1d928acaaddd4eaa28c6a22f7bd6457b379 Mon Sep 17 00:00:00 2001 From: Bernhard Voelker 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