On Wed, Mar 19, 2014 at 08:06:45PM +0100, David Herrmann wrote: > Hi > > This series introduces the concept of "file sealing". Sealing a file restricts > the set of allowed operations on the file in question. Multiple seals are > defined and each seal will cause a different set of operations to return EPERM > if it is set. The following seals are introduced: > > * SEAL_SHRINK: If set, the inode size cannot be reduced > * SEAL_GROW: If set, the inode size cannot be increased > * SEAL_WRITE: If set, the file content cannot be modified > > Unlike existing techniques that provide similar protection, sealing allows > file-sharing without any trust-relationship. This is enforced by rejecting seal > modifications if you don't own an exclusive reference to the given file. So if > you own a file-descriptor, you can be sure that no-one besides you can modify > the seals on the given file. This allows mapping shared files from untrusted > parties without the fear of the file getting truncated or modified by an > attacker. > > Several use-cases exist that could make great use of sealing: > > 1) Graphics Compositors > If a graphics client creates a memory-backed render-buffer and passes a > file-decsriptor to it to the graphics server for display, the server > _has_ to setup SIGBUS handlers whenever mapping the given file. Otherwise, > the client might run ftruncate() or O_TRUNC on the on file in parallel, > thus crashing the server. > With sealing, a compositor can reject any incoming file-descriptor that > does _not_ have SEAL_SHRINK set. This way, any memory-mappings are > guaranteed to stay accessible. Furthermore, we still allow clients to > increase the buffer-size in case they want to resize the render-buffer for > the next frame. We also allow parallel writes so the client can render new > frames into the same buffer (client is responsible of never rendering into > a front-buffer if you want to avoid artifacts). > > Real use-case: Wayland wl_shm buffers can be transparently converted Very nice, the Enlightenment developers have been asking for something like this for a while, it should help them out a lot as well. And thanks for the man pages and test code, if only all new apis came with that already... greg k-h -- 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>