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From: Pavel Raiskup <praiskup@redhat.com>
Date: Sat, 15 Aug 2015 04:40:57 -0400
Subject: install-sh: avoid (low risk) race in /tmp
Ensure that nobody can cross privilege boundaries by pre-creating
symlink on '$tmpdir' path.
Just testing 'mkdir -p' by creating '/tmp/ins$RANDOM-$$/d' is not
safe because '/tmp' directory is usually world-writeable and
'/tmp/ins$RANDOM-$$' content could be pretty easily guessed by
attacker (at least for shells where $RANDOM is not supported).
So, as the first step, create the '/tmp/ins$RANDOM-$$' without -p.
This step would fail early if somebody wanted catch us.
Note that systems that implement (and have enabled)
fs.protected_symlinks kernel feature are not affected even without
this commit.
References:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=760455
https://bugzilla.redhat.com/show_bug.cgi?id=1140725
* lib/install-sh: Implement safer 'mkdir -p' test by running
'$mkdirprog $mkdir_mode "$tmpdir"' first.
(scriptversion): Bump.
--- a/lib/install-sh
+++ b/lib/install-sh
@@ -345,34 +345,41 @@ do
# is incompatible with FreeBSD 'install' when (umask & 300) != 0.
;;
*)
+ # $RANDOM is not portable (e.g. dash); use it when possible to
+ # lower collision chance
tmpdir=${TMPDIR-/tmp}/ins$RANDOM-$$
- trap 'ret=$?; rmdir "$tmpdir/d" "$tmpdir" 2>/dev/null; exit $ret' 0
+ trap 'ret=$?; rmdir "$tmpdir/a/b" "$tmpdir/a" "$tmpdir" 2>/dev/null; exit $ret' 0
+ # As "mkdir -p" follows symlinks and we work in /tmp possibly; so
+ # create the $tmpdir first (and fail if unsuccessful) to make sure
+ # that nobody tries to guess the $tmpdir name.
if (umask $mkdir_umask &&
- exec $mkdirprog $mkdir_mode -p -- "$tmpdir/d") >/dev/null 2>&1
+ $mkdirprog $mkdir_mode "$tmpdir" &&
+ exec $mkdirprog $mkdir_mode -p -- "$tmpdir/a/b") >/dev/null 2>&1
then
if test -z "$dir_arg" || {
# Check for POSIX incompatibilities with -m.
# HP-UX 11.23 and IRIX 6.5 mkdir -m -p sets group- or
# other-writable bit of parent directory when it shouldn't.
# FreeBSD 6.1 mkdir -m -p sets mode of existing directory.
- ls_ld_tmpdir=`ls -ld "$tmpdir"`
+ test_tmpdir="$tmpdir/a"
+ ls_ld_tmpdir=`ls -ld "$test_tmpdir"`
case $ls_ld_tmpdir in
d????-?r-*) different_mode=700;;
d????-?--*) different_mode=755;;
*) false;;
esac &&
- $mkdirprog -m$different_mode -p -- "$tmpdir" && {
- ls_ld_tmpdir_1=`ls -ld "$tmpdir"`
+ $mkdirprog -m$different_mode -p -- "$test_tmpdir" && {
+ ls_ld_tmpdir_1=`ls -ld "$test_tmpdir"`
test "$ls_ld_tmpdir" = "$ls_ld_tmpdir_1"
}
}
then posix_mkdir=:
fi
- rmdir "$tmpdir/d" "$tmpdir"
+ rmdir "$tmpdir/a/b" "$tmpdir/a" "$tmpdir"
else
# Remove any dirs left behind by ancient mkdir implementations.
- rmdir ./$mkdir_mode ./-p ./-- 2>/dev/null
+ rmdir ./$mkdir_mode ./-p ./-- "$tmpdir" 2>/dev/null
fi
trap '' 0;;
esac;;
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