"J. Bruce Fields" <bfields@xxxxxxxxxxxx> writes: >> > Secondly when using an NFSv3 R/O lower layer the filesystem permissions >> > check refuses permission to write to the inode which prevents us from >> > copying it up even though we have a writable upper layer. (With an ext4 >> > lower layer the inode check will succeed if the inode is writable even >> > if the filesystem is not.) It is not clear what the right solution is >> > here. One approach is to check the inode permissions only (avoiding the >> > filesystem specific permissions op), but it is not clear we can rely on >> > these for all underlying filesystems. Perhaps this check should only be >> > used for NFS. > > Then couldn't you for example end up circumventing ACLs on the > underlying file to access data cached by reads from another user on the > same system? Ignoring ACL's should always give less access, isn't that right? > > Is it possible to arrange that the check for a readonly filesystem be > done only by the vfs and not also by ->permission? You'd need to modify NFS servers for that to work, no? It's possible but not practical. Thanks, Miklos > > --b. > >> > Perhaps it needs to be a mount option. The second patch >> > (for discussion) following this email implements this, using the inode >> > permissions when the lowerlayer is read-only. This seems to work as >> > expected in my limited testing. >> >> I fear that will create an inconsistency between the read-only and the >> non-read-only case, even though both should behave the same. >> >> I think the cleanest would be to create a mount option to always use >> generic_permission (on both the lower and the upper fs). That would >> give us two, slightly different, operating modes but each would be >> self consistent. >> >> Thanks, >> Miklos >> -- >> 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 -- 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
