On Tue, 2009-05-12 at 14:04 -0400, Stephen Smalley wrote: > On Tue, 2009-05-12 at 11:03 -0700, Joel Becker wrote: > > On Tue, May 12, 2009 at 01:32:47PM -0400, Stephen Smalley wrote: > > > On Tue, 2009-05-12 at 10:22 -0700, Joel Becker wrote: > > > > On Tue, May 12, 2009 at 08:18:34AM -0400, Stephen Smalley wrote: > > > > > Is preserve_security supposed to also control the preservation of the > > > > > SELinux security attribute (security.selinux extended attribute)? I'd > > > > > expect that either we preserve all the security-relevant attributes or > > > > > none of them. And if that is the case, then SELinux has to know about > > > > > preserve_security in order to know what the security context of the new > > > > > inode will be. > > > > > > > > Thank you Stephen, you read my mind. In the ocfs2 case, we're > > > > expecting to just reflink the extended attribute structures verbatim in > > > > the preserve_security case. > > > > > > And in the preserve_security==0 case, you'll be calling > > > security_inode_init_security() in order to get the attribute name/value > > > pair to assign to the new inode just as in the normal file creation > > > case? > > > > Oh, absolutely. > > As an aside, do inodes ever have more than one security.* > > attribute? It would appear that security_inode_init_security() just > > returns one attribute, but what if I had a system running under SMACK > > and then changed to SELinux? Would my (existing) inode then have > > security.smack and security.selinux attributes? > > No, there would be no security.selinux attribute and the file would be > treated as having a well-defined 'unlabeled' attribute by SELinux. Not > something you have to worry about. > > > > > > Also, if you are going to automatically degrade reflink(2) behavior > > > > > based on the owner_or_cap test, then you ought to allow the same to be > > > > > true if the security module vetoes the attempt to preserve attributes. > > > > > Either DAC or MAC logic may say that security attributes cannot be > > > > > preserved. Your current logic will only allow graceful degradation in > > > > > the DAC case, but the MAC case will remain a hard failure. > > > > > > > > I did not think of this, and its a very good point as well. I'm > > > > not sure how to have the return value of security_inode_reflink() > > > > distinguish between "disallow the reflink" and "disallow > > > > preserve_security". But since !preserve_security requires read access > > > > only, perhaps we move security_inode_reflink up higher and say: > > > > > > > > error = security_inode_reflink(old_dentry, dir); > > > > if (error) > > > > preserve_security = 0; > > > > > > > > Here security_inode_reflink() does not need new_dentry, because it isn't > > > > setting a security context. If it's ok with the reflink, we'll be > > > > copying the extended attribute. If it's not OK, it falls through to the > > > > inode_permission(inode, MAY_READ) check, which will check for plain old > > > > read access. > > > > What do we think? > > > > > > I'd rather have two hooks, one to allow the security module to override > > > preserve_security and one to allow the security module to deny the > > > operation altogether. The former hook only needs to be called if > > > preserve_security is not already cleared by the DAC logic. The latter > > > hook needs to know the final verdict on preserve_security in order to > > > determine the right set of checks to apply, which isn't necessarily > > > limited to only checking read access. > > > > Ok, is that two hooks or one hook with specific error returns? > > I don't care, it's up to the LSM group. I just can't come up with a > > good distinguishing set of names if its two hooks :-) > > I suppose you could coalesce them into a single hook ala: > error = security_inode_reflink(old_dentry, dir, &preserve_security); > if (error) > return (error); On second thought (agreeing with Andy about making the interface explicit wrt preserve_security), I don't expect us to ever override preserve_security from SELinux, so you can just pass it in by value. -- Stephen Smalley National Security Agency -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
