Messages in this thread | | | Subject | Re: [PATCH 2/2] sysctl: Restore the selinux path based label lookup for sysctls. | From | Stephen Smalley <> | Date | Thu, 08 Feb 2007 13:13:24 -0500 |
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On Thu, 2007-02-08 at 10:53 -0700, Eric W. Biederman wrote: > Stephen Smalley <sds@tycho.nsa.gov> writes: > > > > > Hmmm...turns out to not be quite enough, as the /proc/sys inodes aren't > > truly private to the fs, so we can run into them in a variety of > > security hooks beyond just the inode hooks, such as > > security_file_permission (when reading and writing them via the vfs > > helpers), security_sb_mount (when mounting other filesystems on > > directories in proc like binfmt_misc), and deeper within the security > > module itself (as in flush_unauthorized_files upon inheritance across > > execve). So I think we have to add an IS_PRIVATE() guard within > > SELinux, as below. Note however that the use of the private flag here > > could be confusing, as these inodes are _not_ private to the fs, are > > exposed to userspace, and security modules must implement the sysctl > > hook to get any access control over them. > > Agreed, the naming is confusing, and using private here doesn't quite > feel right. > > A practical question is: Will we ever encounter these inodes > in the inode_init() path from superblock_init?
Possibly, during setup upon initial policy load (initiated by /sbin/init these days) from selinux_complete_init, as early userspace may have already been accessing them.
> If all of the accesses > that we care about go through inode_doinit_with_dentry we can just > walk the dcache to get the names, and that should work for the normal > proc case as well.
Walking the proc_dir_entry tree (or the ctl_table tree) is preferable as it is a stable, user-immutable representation. Also avoids taking the dcache lock.
> A somewhat related question: How do you handle security labels for > sysfs? No fine grained security yet.
Right, they are all mapped to a single label presently. I was thinking of handling that from userspace after introducing a setxattr handler for sysfs and a way to preserve the SID on the entry (likely caching it in the sysfs_dirent and propagating that to the inode when the inode is populated from the sysfs_dirent). Then early userspace could walk sysfs and apply finer-grained labeling from a configuration.
> If it doesn't look easy to solve this another way I will certainly > go with marking the inodes private.
-- Stephen Smalley National Security Agency
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