On Thu, Mar 20, 2014 at 04:48:30PM +0100, David Herrmann wrote: > On Thu, Mar 20, 2014 at 4:32 PM, <tytso@xxxxxxx> wrote: > > Why not make sealing an attribute of the "struct file", and enforce it > > at the VFS layer? That way all file system objects would have access > > to sealing interface, and for memfd_shmem, you can't get another > > struct file pointing at the object, the security properties would be > > identical. > > Sealing as introduced here is an inode-attribute, not "struct file". > This is intentional. For instance, a gfx-client can get a read-only FD > via /proc/self/fd/ and pass it to the compositor so it can never > overwrite the contents (unless the compositor has write-access to the > inode itself, in which case it can just re-open it read-write). Hmm, good point. I had forgotten about the /proc/self/fd hole. Hmm... what if we have a SEAL_PROC which forces the permissions of /proc/self/fd to be 000? So if it is a property of the attribute, SEAL_WRITE and SEAL_GROW is basically equivalent to using chattr to set the immutable and append-only attribute, except for the "you can't undo the seal unless you have exclusive access to the inode" magic. That does make it pretty memfd_create specific and not a very general API, which is a little unfortunate; hence why I'm trying to explore ways of making a bit more generic and hopefully useful for more use cases. Cheers, - Ted -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>