My company asked me today to set up a user that is allowed only to upload files via sftp. This got me thinking, an sftp user has shell access as well, of course, and this can lead to all kinds of interesting things (the kernel privilege escalation from last week comes to mind). I figured it might be appropriate to run this user as a confined user, at least at a minimum running the user as user_u would block a lot of options, or perhaps a different user I haven't researched them all yet. Now the question is, would SELinux be an appropriate place for an sftp_u user? What I am envisioning is a confined user, that allows only the sftp subsystem to be run and files to be uploaded to the confined users homedir. It seems to me that SELinux would be a good fit for this, but I am merely an amateur here :). Anyone ever done anything like this? Would this be an easy thing? There are of course other options, folks have written programs to confine a user to only uploading via sftp, rssh and others. -Erinn -- selinux mailing list selinux(a)lists.fedoraproject.org https://admin.fedoraproject.org/mailman/listinfo/selinux

On Wed, 2012-02-08 at 14:15 +0000, Miroslav Grepl wrote: > What OS? > > We have sftp+chroot+SELinux in Fedora16/17/RHEL6.2. You could chroot > users in their home directories and then after sftp on a machine, a > user will run in the "chroot_user_t" domain. > > This domain has these accesses by default > > userdom_read_user_home_content_files(chroot_user_t) > userdom_read_inherited_user_home_content_files(chroot_user_t) > userdom_read_user_home_content_symlinks(chroot_user_t) > userdom_exec_user_home_content_files(chroot_user_t > > and the "ssh_chroot_rw_homedirs" boolean. > You might want to write a blog about how this is supposed to work and how chroot_user_t differs from sftpd_t.

> > -- > selinux mailing list > selinux(a)lists.fedoraproject.org > https://admin.fedoraproject.org/mailman/listinfo/selinux -- selinux mailing list selinux(a)lists.fedoraproject.org https://admin.fedoraproject.org/mailman/listinfo/selinux

On 02/08/2012 05:15 AM, Miroslav Grepl wrote: > On 02/08/2012 01:31 AM, Erinn Looney-Triggs wrote: >> My company asked me today to set up a user that is allowed only to >> upload files via sftp. This got me thinking, an sftp user has shell >> access as well, of course, and this can lead to all kinds of interesting >> things (the kernel privilege escalation from last week comes to mind). >> >> I figured it might be appropriate to run this user as a confined user, >> at least at a minimum running the user as user_u would block a lot of >> options, or perhaps a different user I haven't researched them all yet. >> >> Now the question is, would SELinux be an appropriate place for an sftp_u >> user? What I am envisioning is a confined user, that allows only the >> sftp subsystem to be run and files to be uploaded to the confined users >> homedir. It seems to me that SELinux would be a good fit for this, but I >> am merely an amateur here :). >> >> Anyone ever done anything like this? Would this be an easy thing? >> >> There are of course other options, folks have written programs to >> confine a user to only uploading via sftp, rssh and others. >> >> -Erinn >> >> >> -- >> selinux mailing list >> selinux@lists.fedoraproject.org<mailto:selinux@lists.fedoraproject.org> >> https://admin.fedoraproject.org/mailman/listinfo/selinux > What OS? > > We have sftp+chroot+SELinux in Fedora16/17/RHEL6.2. You could chroot > users in their home directories and then after sftp on a machine, a user > will run in the "chroot_user_t" domain. > > This domain has these accesses by default > > userdom_read_user_home_content_files(chroot_user_t) > userdom_read_inherited_user_home_content_files(chroot_user_t) > userdom_read_user_home_content_symlinks(chroot_user_t) > userdom_exec_user_home_content_files(chroot_user_t > > and the "ssh_chroot_rw_homedirs" boolean. > > > > RHEL 6.2, it looks like between your suggestions and Dominick's suggestions I can probably put together a pretty good little sandbox for an sftp user, without of course, having to become the master of the universe that can write policy ;). Thanks for all the good info, -Erinn

On 02/08/2012 08:58 AM, Miroslav Grepl wrote: > On 02/08/2012 06:38 PM, Erinn Looney-Triggs wrote: >> On 02/08/2012 05:15 AM, Miroslav Grepl wrote: >>> On 02/08/2012 01:31 AM, Erinn Looney-Triggs wrote: >>>> My company asked me today to set up a user that is allowed only to >>>> upload files via sftp. This got me thinking, an sftp user has shell >>>> access as well, of course, and this can lead to all kinds of >>>> interesting >>>> things (the kernel privilege escalation from last week comes to mind). >>>> >>>> I figured it might be appropriate to run this user as a confined user, >>>> at least at a minimum running the user as user_u would block a lot of >>>> options, or perhaps a different user I haven't researched them all yet. >>>> >>>> Now the question is, would SELinux be an appropriate place for an >>>> sftp_u >>>> user? What I am envisioning is a confined user, that allows only the >>>> sftp subsystem to be run and files to be uploaded to the confined users >>>> homedir. It seems to me that SELinux would be a good fit for this, >>>> but I >>>> am merely an amateur here :). >>>> >>>> Anyone ever done anything like this? Would this be an easy thing? >>>> >>>> There are of course other options, folks have written programs to >>>> confine a user to only uploading via sftp, rssh and others. >>>> >>>> -Erinn >>>> >>>> >>>> -- >>>> selinux mailing list >>>> selinux@lists.fedoraproject.org<mailto:selinux@lists.fedoraproject.org> >>>> https://admin.fedoraproject.org/mailman/listinfo/selinux >>> What OS? >>> >>> We have sftp+chroot+SELinux in Fedora16/17/RHEL6.2. You could chroot >>> users in their home directories and then after sftp on a machine, a user >>> will run in the "chroot_user_t" domain. >>> >>> This domain has these accesses by default >>> >>> userdom_read_user_home_content_files(chroot_user_t) >>> userdom_read_inherited_user_home_content_files(chroot_user_t) >>> userdom_read_user_home_content_symlinks(chroot_user_t) >>> userdom_exec_user_home_content_files(chroot_user_t >>> >>> and the "ssh_chroot_rw_homedirs" boolean. >>> >>> >>> >>> >> RHEL 6.2, it looks like between your suggestions and Dominick's >> suggestions I can probably put together a pretty good little sandbox for >> an sftp user, without of course, having to become the master of the >> universe that can write policy ;). >> >> Thanks for all the good info, >> >> -Erinn >> >> > Petr Lautrbach (openssh package maintainer) is just writing a blog how > to setup it. I am going to post his blog tomorrow. Well that is just wonderful, thanks Miroslav and thank Petr for me.

-Erinn

On Thu, 2012-02-09 at 16:30 +0100, Miroslav Grepl wrote: > Here is: > > http://bachradsusi.livejournal.com/2239.html >> -Erinn >> >> Thanks verified. Only thing to keep in mind is to restorecon -R -v /home/sftponlyuser

made a screencast of the process while verifying: http://youtu.be/KJVlis1uwIg -- selinux mailing list selinux(a)lists.fedoraproject.org https://admin.fedoraproject.org/mailman/listinfo/selinux