On Tue, Aug 17, 2021 at 02:33:01PM -0700, Jaegeuk Kim wrote: > On 08/17, Eric Biggers wrote: > > On Tue, Aug 17, 2021 at 11:57:46AM -0700, Jaegeuk Kim wrote: > > > On 08/17, Christoph Hellwig wrote: > > > > On Mon, Aug 16, 2021 at 07:03:21PM -0700, Eric Biggers wrote: > > > > > Freeing preallocated blocks on error would be better than nothing, although note > > > > > that the preallocated blocks may have filled an arbitrary sequence of holes -- > > > > > so simply truncating past EOF would *not* be sufficient. > > > > > > > > > > But really filesystems need to be designed to never expose uninitialized data, > > > > > even if I/O errors or a sudden power failure occurs. It is unfortunate that > > > > > f2fs apparently wasn't designed with that goal in mind. > > > > > > > > > > In any case, I don't think we can proceed with any other f2fs direct I/O > > > > > improvements until this data leakage bug can be solved one way or another. If > > > > > my patch to remove support for allocating writes isn't acceptable and the > > > > > desired solution is going to require some more invasive f2fs surgery, are you or > > > > > Chao going to work on it? I'm not sure there's much I can do here. > > > > > > > > Btw, this is generally a problem for buffered I/O as well, although the > > > > window for exposing uninitialized blocks on a crash tends to be smaller. > > > > > > How about adding a warning message when we meet an error with preallocated > > > unwritten blocks? In the meantime, can we get the Eric's patches for iomap > > > support? I feel that we only need to modify the preallocation and error > > > handling parts? > > > > A warning message would do nothing to prevent uninitialized blocks from being > > leaked to userspace. > > To give a signal that it's a known issue that we'll fix later. > This bug is concerning mainly because it's a security vulnerability: anyone with read+write access to just one file on an f2fs filesystem can effectively read all other files on that filesystem. A warning message wouldn't change that. And even in the case of this bug breaking a non-malicious program, hardly anyone reads kernel log messages anyway. If something is broken, having a log message that says "yeah, this is broken, sorry" isn't going to accomplish much... - Eric
