On 04/24/2018 11:22 AM, David Howells wrote: > Stephen Smalley <[email protected]> wrote: > >> Neither fsopen() nor fscontext_fs_write() appear to perform any kind of >> up-front permission checking (DAC or MAC), although some security hooks may >> be ultimately called to allocate structures, parse security options, etc. >> Is there a reason not apply a may_mount() or similar check up front? > > may_mount() is called by fsmount() at the moment. It may make sense to move > this earlier to fsopen(). Note that there's also going to be something that > looks like: > > fd = fspick("/mnt"); > fsmount(fd, "/a", MNT_NOEXEC); // ie. bind mount > > or: > > fd = fspick("/mnt"); > write(fd, "o intr"); > write(fd, "x reconfigure"); // ie. something like remount > close(fd); > > I guess we'd want to call may_mount() in fspick() too. But there's also the > possibility of using this to create a query interfact too: > > fd = fspick("/mnt"); > write(fd, "q intr"); > read(fd, value_buffer);
My concern was that fsopen()/fscontext_fs_write() may expose attack surface (e.g. mount option parsing code) that might not be normally accessible to unprivileged userspace (i.e. gated by may_mount() and security_sb_mount()) prior to your changes.
