On Fri, Jun 03, 2011 at 01:06:32AM -0400, Mimi Zohar wrote: > On Fri, 2011-06-03 at 12:21 +1000, Dave Chinner wrote: > > On Thu, Jun 02, 2011 at 08:23:31AM -0400, Mimi Zohar wrote: > > > Initialize 'security.evm' for new files. Reduce number of arguments > > > by defining 'struct xattr'. > > > > why does this need a new security callout from every filesystem? > > Once the security xattr is initialised, the name, len and value is > > not going to change so surely the evm xattr can be initialised at > > the same time the lsm xattr is initialised. > > Steve Whitehouse asked a similar question, suggesting that > security_inode_init_security() return a vector of xattrs to minimize the > number of xattr writes. Casey pointed out the "stacking" of LSMs will > result in multiple calls to security_inode_init_security(), once for > each LSM. The conclusion (http://lkml.org/lkml/2011/5/19/125) was: > > Moving evm_inode_init_security() into security_inode_init_security() > only works for the single LSM and EVM case, but not for the multiple > LSMs and EVM case, as the 'stacker' would call each LSM's > security_inode_iint_security(). Having the 'stacker' return an array of > xattrs would make sense and, at the same time, resolve the EVM issue. In > evm_inode_post_init_security(), EVM could then walk the list of xattrs. But that does not change the fact that ther eis a _single external call_ from the filesystem to security_inode_init_security(), and the attribute (array) that it returns is only read by evm_inode_post_init_security() to calculate a new attribute. If evm_inode_post_init_security() only needs to read the security attributes, then why does it need to be calculated _after_ the security attributes are written to the filesystem inode? i.e, your current code is: security_inode_init_security(&lsm_xattr) set_xattr(&lsm_xattr) evm_inode_post_init_security(&lsm_xattr, &evm_xattr) set_xattr(&evm_xattr) and I'm asking why you can't do it like this: security_inode_init_security(&lsm_xattr, &evm_xattr) set_xattr(&lsm_xattr) set_xattr(&evm_xattr) where security_inode_init_security() calls: evm_inode_post_init_security(&lsm_xattr, &evm_xattr) before returning to calculate the evm xattr? Indeed, if we are stacking LSMs, the iteration must occur internally to security_inode_init_security(), and so that would mean the entire stacking/multiple attr thing could be handled simply by passing an array and having the EVM xattr always be the last in the array. i.e.: XXXfs_init_security() { xattr_count = security_inode_init_security(&xattr_array) for (i = 0; i < xattr_count; i++) set_xattr(&xattr_array[i]) security_free_xattr(&xattr_array); } And then the filesystems need to know _nothing at all_ about the internals of the security subsystem or how it uses xattrs or even whether EVM is enabled or active or neither. This is far cleaner than spewing security-flavour-of-the-month junk widely across the tree... This also makes it possible for the filesystems to atomically set or fail to set all the security attributes in one operation/transaction, which will help guarantee the integrity of the system in the face of externally induced failures. > > Then all you need to do in each filesystem is add the evm_xattr > > structure to the existing security init call and a: > > > > #ifdef CONFIG_EVM > > /* set evm.xattr */ > > #endif > > > > to avoid adding code that is never executed when EVM is not > > configured into the kernel. > > > > That way you don't create the lsm_xattr at all if the evm_xattr is > > not created, and then the file creation should fail in an atomic > > manner, right? i.e. you don't leave files with unverified security > > attributes around when interesting failure corner cases occur (e.g. > > ENOSPC). > > That would imply EVM must be enabled for all LSMs that define a security > xattr. That's definitely a good goal, but probably not a good idea for > right now. > > > And while you are there, it's probably also be a good idea to add > > support for all filesystems that support xattrs, not just a random > > subset of them... > > > > Cheers, > > > > Dave. > > The EVM xattr is initialized based on the LSM xattr. At this point, as > far as I'm aware, the only remaining filesystems that call > security_inode_init_security() to initialize the LSM xattr, are ocfs2 > and reiserfs. Both of which might have memory leaks. Tiger Yang is > addressing the memory leak for ocfs2. I don't follow you - I didn't see any patches that remove security_inode_init_security() from any of the filesystems, so they all still call that function.... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- 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
