On Thu, Feb 21, 2019 at 03:28:37PM -0500, Stephen Smalley wrote:
> On 2/21/19 2:44 PM, Dominick Grift wrote:
> > On Thu, Feb 21, 2019 at 02:34:38PM -0500, Stephen Smalley wrote:
> > > On 2/21/19 1:42 PM, Stephen Smalley wrote:
> > > > Derived in part from a patch by Dominick Grift.
> > > >
> > > > The MDP example no longer works on modern systems. Fix it.
> > > > While we are at it, add MLS support and enable it.
> > > >
> > > > NB This still does not work on systems using dbus-daemon instead of
> > > > dbus-broker because dbus-daemon does not yet gracefully handle unknown
> > > > classes/permissions. This is a deficiency in libselinux's
> > > > selinux_set_mapping() interface and underlying implementation,
> > > > which was never fully updated to deal with unknown classes/permissions
> > > > unlike the kernel. Programs that instead use selinux_check_access()
> > > > like dbus-broker do not have this problem.
> > >
> > > We could perhaps avoid this problem by having mdp always include at least a
> > > core set of userspace classes/permissions in the policy it generates. We
> > > could also fix libselinux but that won't help on any existing distro.
> > >
> > > >
> > > > Other known issues:
> > > > - Not everything appears to be relabeled, so some files are left with invalid
> > > > contexts and remapped to the unlabeled SID/context.
> > >
> > > This appears to be partly due to overuse of <<none>> in file_contexts (.fc)
> > > files. That excludes those parts of the filesystem from being relabeled at
> > > all. This was used to exclude pseudo filesystems (obsoleted by seclabel
> > > mount option detection) or runtime directories/files whose labels were
> > > derived from the creating process and couldn't be statically specified by
> > > file_contexts. To get my system back into working order even with targeted
> > > policy, I had to strip all <<none>> entries out of my file_contexts* files
> > > and then run setfiles -F with the list of filesystem mounts to relabel.
> > > Otherwise, I'd have files left in the old contexts and the system wouldn't
> > > even come up to user login, even if permissive.
> >
> > What <<none>> spec(s) in fedora would be so important that it causes the system to not come up to user login, even in permissive?
> > Does the unlabeled isid not address these particular scenario's? and why not?
>
> Yes, I don't fully understand it myself; I just know that certain services
> won't start successfully and it never reaches the point where I can login
> locally or remotely. But stripping the <<none>> entries and running
> setfiles -F did fix it for me. NB This was for converting back from mdp to
> the Fedora targeted policy. It wouldn't be an issue for converting to mdp
> since that file_contexts has no <<none>> entries and has a default match for
> /.*.
I am going on a limb here so bear with me but; I suspect that it was not the <<none>> that "did" it. I think it might have been the additional setfiles -F that did it.
I think the services did not come up because systemd was not able to compute its context from /sbin/init.
If the above is actually the case then my question is:
Why can't systemd compute its context from /sbin/init by relying on the unlabeled isid. I mean if /sbin/init was mislabeled. then the unlabeled isid should have kicked in. So why was systemd unable to use that to compute its context?
>
> Maybe it is a case of processes with CAP_MAC_ADMIN fetching the raw context
> (which is invalid under the current policy) and then trying to feed them
> back to the kernel via a selinuxfs interface, e.g. security_compute_create()
> or similar. The kernel would reject those.
>
> >
> > I am testing the patch now here (but in my scenario its a very minimal fedora with dssp2-standard policy)
> >
> > >
> > > FWIW, Android policy doesn't use <<none>> at all. But they also don't have
> > > a /.* or equivalent entry as a default match, so anything not covered by a
> > > more specific match is likewise not labeled. seapp_contexts handles the more
> > > dynamic aspect of app directory labeling for Android.
> > >
> > > The other problem case for relabeling is the mount point directories, which
> > > requires unmounting them all and relabeling them if we care. Otherwise
> > > they'll just get the unlabeled context and as long as we allow mounting on
> > > that, it should be ok.
> > >
> > > > - X will fail due to lack of a x_contexts file
> > > > - libvirtd will fail due to lack of a virtual_domain_context file
> > >
> > > We could easily add these to the mdp policy.
> > >
> > > > - crond reports an error with "No security context"
> > >
> > > This is probably due to the lack of a contexts/default_contexts or any
> > > contexts/users/ files in the dummy policy.
> > >
> > > >
> > > > Changes to mdp:
> > > > Add support for devtmpfs, required by modern Linux distributions.
> > > > Add MLS support, with sample sensitivities, categories, and constraints.
> > > > Generate fs_use and genfscon rules based on kernel configuration.
> > > > Update list of filesystem types for fs_use and genfscon rules.
> > > > Use object_r for object contexts.
> > > >
> > > > Changes to install_policy.sh:
> > > > Bail immediately on any errors.
> > > > Provide more helpful error messages when unable to find userspace tools.
> > > > Refuse to run if SELinux is already enabled.
> > > > Unconditionally move aside /etc/selinux/config and create a new one.
> > > > Build policy with -U allow so that userspace object managers do not break.
> > > > Build policy with MLS enabled by default.
> > > > Add default seusers mapping and failsafe context for use by
> > > > pam_selinux / libselinux.
> > > > Set to permissive mode rather than enforcing to permit initial autorelabel.
> > > > Update the list of filesystem types to be relabeled.
> > > > Create /.autorelabel to trigger an autorelabel on reboot.
> > > > Drop broken attempt to relabel the /dev mountpoint directory.
> > > >
> > > > Signed-off-by: Stephen Smalley <sds@xxxxxxxxxxxxx>
> > > > ---
> > > > scripts/selinux/install_policy.sh | 82 ++++++++-------
> > > > scripts/selinux/mdp/mdp.c | 164 +++++++++++++++++++++++++-----
> > > > 2 files changed, 183 insertions(+), 63 deletions(-)
> > > >
> > > > diff --git a/scripts/selinux/install_policy.sh b/scripts/selinux/install_policy.sh
> > > > index 0b86c47baf7d..09eab4d0da5c 100755
> > > > --- a/scripts/selinux/install_policy.sh
> > > > +++ b/scripts/selinux/install_policy.sh
> > > > @@ -1,30 +1,51 @@
> > > > #!/bin/sh
> > > > # SPDX-License-Identifier: GPL-2.0
> > > > +set -e
> > > > if [ `id -u` -ne 0 ]; then
> > > > echo "$0: must be root to install the selinux policy"
> > > > exit 1
> > > > fi
> > > > +
> > > > SF=`which setfiles`
> > > > if [ $? -eq 1 ]; then
> > > > - if [ -f /sbin/setfiles ]; then
> > > > - SF="/usr/setfiles"
> > > > - else
> > > > - echo "no selinux tools installed: setfiles"
> > > > - exit 1
> > > > - fi
> > > > + echo "Could not find setfiles"
> > > > + echo "Do you have policycoreutils installed?"
> > > > + exit 1
> > > > fi
> > > > -cd mdp
> > > > -
> > > > CP=`which checkpolicy`
> > > > +if [ $? -eq 1 ]; then
> > > > + echo "Could not find checkpolicy"
> > > > + echo "Do you have checkpolicy installed?"
> > > > + exit 1
> > > > +fi
> > > > VERS=`$CP -V | awk '{print $1}'`
> > > > -./mdp policy.conf file_contexts
> > > > -$CP -o policy.$VERS policy.conf
> > > > +ENABLED=`which selinuxenabled`
> > > > +if [ $? -eq 1 ]; then
> > > > + echo "Could not find selinuxenabled"
> > > > + echo "Do you have libselinux-utils installed?"
> > > > + exit 1
> > > > +fi
> > > > +
> > > > +if selinuxenabled; then
> > > > + echo "SELinux is already enabled"
> > > > + echo "This prevents safely relabeling all files."
> > > > + echo "Boot with selinux=0 on the kernel command-line or"
> > > > + echo "SELINUX=disabled in /etc/selinux/config."
> > > > + exit 1
> > > > +fi
> > > > +
> > > > +cd mdp
> > > > +./mdp -m policy.conf file_contexts
> > > > +$CP -U allow -M -o policy.$VERS policy.conf
> > > > mkdir -p /etc/selinux/dummy/policy
> > > > mkdir -p /etc/selinux/dummy/contexts/files
> > > > +echo "__default__:user_u" > /etc/selinux/dummy/seusers
> > > > +echo "base_r:base_t" > /etc/selinux/dummy/contexts/failsafe_context
> > > > +
> > > > cp file_contexts /etc/selinux/dummy/contexts/files
> > > > cp dbus_contexts /etc/selinux/dummy/contexts
> > > > cp policy.$VERS /etc/selinux/dummy/policy
> > > > @@ -33,37 +54,22 @@ FC_FILE=/etc/selinux/dummy/contexts/files/file_contexts
> > > > if [ ! -d /etc/selinux ]; then
> > > > mkdir -p /etc/selinux
> > > > fi
> > > > -if [ ! -f /etc/selinux/config ]; then
> > > > - cat > /etc/selinux/config << EOF
> > > > -SELINUX=enforcing
> > > > +if [ -f /etc/selinux/config ]; then
> > > > + echo "/etc/selinux/config exists, moving to /etc/selinux/config.bak."
> > > > + mv /etc/selinux/config /etc/selinux/config.bak
> > > > +fi
> > > > +echo "Creating new /etc/selinux/config for dummy policy."
> > > > +cat > /etc/selinux/config << EOF
> > > > +SELINUX=permissive
> > > > SELINUXTYPE=dummy
> > > > EOF
> > > > -else
> > > > - TYPE=`cat /etc/selinux/config | grep "^SELINUXTYPE" | tail -1 | awk -F= '{ print $2 '}`
> > > > - if [ "eq$TYPE" != "eqdummy" ]; then
> > > > - selinuxenabled
> > > > - if [ $? -eq 0 ]; then
> > > > - echo "SELinux already enabled with a non-dummy policy."
> > > > - echo "Exiting. Please install policy by hand if that"
> > > > - echo "is what you REALLY want."
> > > > - exit 1
> > > > - fi
> > > > - mv /etc/selinux/config /etc/selinux/config.mdpbak
> > > > - grep -v "^SELINUXTYPE" /etc/selinux/config.mdpbak >> /etc/selinux/config
> > > > - echo "SELINUXTYPE=dummy" >> /etc/selinux/config
> > > > - fi
> > > > -fi
> > > > cd /etc/selinux/dummy/contexts/files
> > > > -$SF file_contexts /
> > > > +$SF -F file_contexts /
> > > > -mounts=`cat /proc/$$/mounts | egrep "ext2|ext3|xfs|jfs|ext4|ext4dev|gfs2" | awk '{ print $2 '}`
> > > > -$SF file_contexts $mounts
> > > > +mounts=`cat /proc/$$/mounts | \
> > > > + egrep "ext[234]|jfs|xfs|reiserfs|jffs2|gfs2|btrfs|f2fs|ocfs2" | \
> > > > + awk '{ print $2 '}`
> > > > +$SF -F file_contexts $mounts
> > > > -
> > > > -dodev=`cat /proc/$$/mounts | grep "/dev "`
> > > > -if [ "eq$dodev" != "eq" ]; then
> > > > - mount --move /dev /mnt
> > > > - $SF file_contexts /dev
> > > > - mount --move /mnt /dev
> > > > -fi
> > > > +touch /.autorelabel
> > > > diff --git a/scripts/selinux/mdp/mdp.c b/scripts/selinux/mdp/mdp.c
> > > > index 073fe7537f6c..daad333c7252 100644
> > > > --- a/scripts/selinux/mdp/mdp.c
> > > > +++ b/scripts/selinux/mdp/mdp.c
> > > > @@ -33,6 +33,7 @@
> > > > #include <unistd.h>
> > > > #include <string.h>
> > > > #include <sys/socket.h>
> > > > +#include <linux/kconfig.h>
> > > > static void usage(char *name)
> > > > {
> > > > @@ -95,10 +96,31 @@ int main(int argc, char *argv[])
> > > > }
> > > > fprintf(fout, "\n");
> > > > - /* NOW PRINT OUT MLS STUFF */
> > > > + /* print out mls declarations and constraints */
> > > > if (mls) {
> > > > - printf("MLS not yet implemented\n");
> > > > - exit(1);
> > > > + fprintf(fout, "sensitivity s0;\n");
> > > > + fprintf(fout, "sensitivity s1;\n");
> > > > + fprintf(fout, "dominance { s0 s1 }\n");
> > > > + fprintf(fout, "category c0;\n");
> > > > + fprintf(fout, "category c1;\n");
> > > > + fprintf(fout, "level s0:c0.c1;\n");
> > > > + fprintf(fout, "level s1:c0.c1;\n");
> > > > +#define SYSTEMLOW "s0"
> > > > +#define SYSTEMHIGH "s1:c0.c1"
> > > > + for (i = 0; secclass_map[i].name; i++) {
> > > > + struct security_class_mapping *map = &secclass_map[i];
> > > > +
> > > > + fprintf(fout, "mlsconstrain %s {\n", map->name);
> > > > + for (j = 0; map->perms[j]; j++)
> > > > + fprintf(fout, "\t%s\n", map->perms[j]);
> > > > + /*
> > > > + * This requires all subjects and objects to be
> > > > + * single-level (l2 eq h2), and that the subject
> > > > + * level dominate the object level (h1 dom h2)
> > > > + * in order to have any permissions to it.
> > > > + */
> > > > + fprintf(fout, "} (l2 eq h2 and h1 dom h2);\n\n");
> > > > + }
> > > > }
> > > > /* types, roles, and allows */
> > > > @@ -108,34 +130,126 @@ int main(int argc, char *argv[])
> > > > for (i = 0; secclass_map[i].name; i++)
> > > > fprintf(fout, "allow base_t base_t:%s *;\n",
> > > > secclass_map[i].name);
> > > > - fprintf(fout, "user user_u roles { base_r };\n");
> > > > - fprintf(fout, "\n");
> > > > + fprintf(fout, "user user_u roles { base_r }");
> > > > + if (mls)
> > > > + fprintf(fout, " level %s range %s - %s", SYSTEMLOW,
> > > > + SYSTEMLOW, SYSTEMHIGH);
> > > > + fprintf(fout, ";\n");
> > > > +
> > > > +#define SUBJUSERROLETYPE "user_u:base_r:base_t"
> > > > +#define OBJUSERROLETYPE "user_u:object_r:base_t"
> > > > /* default sids */
> > > > for (i = 1; i < initial_sid_to_string_len; i++)
> > > > - fprintf(fout, "sid %s user_u:base_r:base_t\n", initial_sid_to_string[i]);
> > > > + fprintf(fout, "sid %s " SUBJUSERROLETYPE "%s\n",
> > > > + initial_sid_to_string[i], mls ? ":" SYSTEMLOW : "");
> > > > fprintf(fout, "\n");
> > > > - fprintf(fout, "fs_use_xattr ext2 user_u:base_r:base_t;\n");
> > > > - fprintf(fout, "fs_use_xattr ext3 user_u:base_r:base_t;\n");
> > > > - fprintf(fout, "fs_use_xattr ext4 user_u:base_r:base_t;\n");
> > > > - fprintf(fout, "fs_use_xattr jfs user_u:base_r:base_t;\n");
> > > > - fprintf(fout, "fs_use_xattr xfs user_u:base_r:base_t;\n");
> > > > - fprintf(fout, "fs_use_xattr reiserfs user_u:base_r:base_t;\n");
> > > > - fprintf(fout, "fs_use_xattr jffs2 user_u:base_r:base_t;\n");
> > > > - fprintf(fout, "fs_use_xattr gfs2 user_u:base_r:base_t;\n");
> > > > +#define FS_USE(behavior, fstype) \
> > > > + fprintf(fout, "fs_use_%s %s " OBJUSERROLETYPE "%s;\n", \
> > > > + behavior, fstype, mls ? ":" SYSTEMLOW : "")
> > > > +
> > > > + /*
> > > > + * Filesystems whose inode labels can be fetched via getxattr.
> > > > + */
> > > > +#ifdef CONFIG_EXT2_FS_SECURITY
> > > > + FS_USE("xattr", "ext2");
> > > > +#endif
> > > > +#ifdef CONFIG_EXT3_FS_SECURITY
> > > > + FS_USE("xattr", "ext3");
> > > > +#endif
> > > > +#ifdef CONFIG_EXT4_FS_SECURITY
> > > > + FS_USE("xattr", "ext4");
> > > > +#endif
> > > > +#ifdef CONFIG_JFS_SECURITY
> > > > + FS_USE("xattr", "jfs");
> > > > +#endif
> > > > +#ifdef CONFIG_REISERFS_FS_SECURITY
> > > > + FS_USE("xattr", "reiserfs");
> > > > +#endif
> > > > +#ifdef CONFIG_JFFS2_FS_SECURITY
> > > > + FS_USE("xattr", "jffs2");
> > > > +#endif
> > > > +#ifdef CONFIG_XFS_FS
> > > > + FS_USE("xattr", "xfs");
> > > > +#endif
> > > > +#ifdef CONFIG_GFS2_FS
> > > > + FS_USE("xattr", "gfs2");
> > > > +#endif
> > > > +#ifdef CONFIG_BTRFS_FS
> > > > + FS_USE("xattr", "btrfs");
> > > > +#endif
> > > > +#ifdef CONFIG_F2FS_FS_SECURITY
> > > > + FS_USE("xattr", "f2fs");
> > > > +#endif
> > > > +#ifdef CONFIG_OCFS2_FS
> > > > + FS_USE("xattr", "ocsfs2");
> > > > +#endif
> > > > +#ifdef CONFIG_OVERLAY_FS
> > > > + FS_USE("xattr", "overlay");
> > > > +#endif
> > > > +#ifdef CONFIG_SQUASHFS_XATTR
> > > > + FS_USE("xattr", "squashfs");
> > > > +#endif
> > > > +
> > > > + /*
> > > > + * Filesystems whose inodes are labeled from allocating task.
> > > > + */
> > > > + FS_USE("task", "pipefs");
> > > > + FS_USE("task", "sockfs");
> > > > - fprintf(fout, "fs_use_task eventpollfs user_u:base_r:base_t;\n");
> > > > - fprintf(fout, "fs_use_task pipefs user_u:base_r:base_t;\n");
> > > > - fprintf(fout, "fs_use_task sockfs user_u:base_r:base_t;\n");
> > > > + /*
> > > > + * Filesystems whose inode labels are computed from both
> > > > + * the allocating task and the superblock label.
> > > > + */
> > > > +#ifdef CONFIG_UNIX98_PTYS
> > > > + FS_USE("trans", "devpts");
> > > > +#endif
> > > > +#ifdef CONFIG_HUGETLBFS
> > > > + FS_USE("trans", "hugetlbfs");
> > > > +#endif
> > > > +#ifdef CONFIG_TMPFS
> > > > + FS_USE("trans", "tmpfs");
> > > > +#endif
> > > > +#ifdef CONFIG_DEVTMPFS
> > > > + FS_USE("trans", "devtmpfs");
> > > > +#endif
> > > > +#ifdef CONFIG_POSIX_MQUEUE
> > > > + FS_USE("trans", "mqueue");
> > > > +#endif
> > > > - fprintf(fout, "fs_use_trans mqueue user_u:base_r:base_t;\n");
> > > > - fprintf(fout, "fs_use_trans devpts user_u:base_r:base_t;\n");
> > > > - fprintf(fout, "fs_use_trans hugetlbfs user_u:base_r:base_t;\n");
> > > > - fprintf(fout, "fs_use_trans tmpfs user_u:base_r:base_t;\n");
> > > > - fprintf(fout, "fs_use_trans shm user_u:base_r:base_t;\n");
> > > > +#define GENFSCON(fstype, prefix) \
> > > > + fprintf(fout, "genfscon %s %s " OBJUSERROLETYPE "%s\n", \
> > > > + fstype, prefix, mls ? ":" SYSTEMLOW : "")
> > > > - fprintf(fout, "genfscon proc / user_u:base_r:base_t\n");
> > > > + /*
> > > > + * Filesystems whose inodes are labeled from path prefix match
> > > > + * relative to the filesystem root. Depending on the filesystem,
> > > > + * only a single label for all inodes may be supported. Here
> > > > + * we list the filesystem types for which per-file labeling is
> > > > + * supported using genfscon; any other filesystem type can also
> > > > + * be added by only with a single entry for all of its inodes.
> > > > + */
> > > > +#ifdef CONFIG_PROC_FS
> > > > + GENFSCON("proc", "/");
> > > > +#endif
> > > > +#ifdef CONFIG_SECURITY_SELINUX
> > > > + GENFSCON("selinuxfs", "/");
> > > > +#endif
> > > > +#ifdef CONFIG_SYSFS
> > > > + GENFSCON("sysfs", "/");
> > > > +#endif
> > > > +#ifdef CONFIG_DEBUG_FS
> > > > + GENFSCON("debugfs", "/");
> > > > +#endif
> > > > +#ifdef CONFIG_TRACING
> > > > + GENFSCON("tracefs", "/");
> > > > +#endif
> > > > +#ifdef CONFIG_PSTORE
> > > > + GENFSCON("pstore", "/");
> > > > +#endif
> > > > + GENFSCON("cgroup", "/");
> > > > + GENFSCON("cgroup2", "/");
> > > > fclose(fout);
> > > > @@ -144,8 +258,8 @@ int main(int argc, char *argv[])
> > > > printf("Wrote policy, but cannot open %s for writing\n", ctxout);
> > > > usage(argv[0]);
> > > > }
> > > > - fprintf(fout, "/ user_u:base_r:base_t\n");
> > > > - fprintf(fout, "/.* user_u:base_r:base_t\n");
> > > > + fprintf(fout, "/ " OBJUSERROLETYPE "%s\n", mls ? ":" SYSTEMLOW : "");
> > > > + fprintf(fout, "/.* " OBJUSERROLETYPE "%s\n", mls ? ":" SYSTEMLOW : "");
> > > > fclose(fout);
> > > > return 0;
> > > >
> > >
> >
>
--
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Dominick Grift
