On Fri, Aug 10, 2018 at 07:54:47PM -0400, Theodore Y. Ts'o wrote: > On Fri, Aug 10, 2018 at 03:12:34PM -0700, Darrick J. Wong wrote: > > Hey now, there was a little more nuance to it than that[1][2]. The > > complaint in the first instance had much more to do with breaking > > existing V4 filesystems by adding format requirements that mkfs didn't > > know about when the filesystem was created. Yes, you can create V4 > > filesystems that will hang the system if the log was totally unformatted > > and metadata updates are made, but OTOH it's fairly obvious when that > > happens, you have to be root to mount a disk filesystem, and we try to > > avoid breaking existing users. > > I wasn't thinking about syzbot reports; I've largely written them off > as far as file system testing is concerned, but rather Wen Xu at > Georgia Tech, who is much more reasonable than Dmitry, and has helpeyd > me out a lot; and has complained that the XFS folks haven't been > engaging with him. Ahh, ok. Yes, Wen has been easier to work with, and gives out filesystem images. Hm, I'll go comb the bugzilla again... > In either case, both security researchers are fuzzing file system > images, and then fixing the checksums, and discovering that this can > lead to kernel crashes, and in a few cases, buffer overruns that can > lead to potential privilege escalations. Wen can generate reports > faster than syzbot, but at least he gives me file system images (as > opposed to having to dig them out of syzbot repro C files) and he > actually does some analysis and explains what he thinks is going on. (FWIW I tried to figure out how to add fs image dumping to syzbot and whoah that was horrifying. > I don't think anyone was claiming that format requirements should be > added to ext4 or xfs file systems. But rather, that kernel code > should be made more robust against maliciously corrupted file system > images that have valid checksums. I've been more willing to work with > Wen; Dave has expressed the opinion that these are not realistic bug > reports, and since only root can mount file systems, it's not high > priority. I don't think they're high priority either, but they're at least worth /some/ attention. > The reason why I bring this up here is that in container land, there > are those who believe that "container root" should be able to mount > file systems, and if the "container root" isn't trusted, the fact that > the "container root" can crash the host kernel, or worse, corrupt the > host kernel and break out of the container as a result, that would be > sad. > > I was pretty sure most file system developers are on the same page > that allowing untrusted "container roots" the ability to mount > arbitrary block device file systems is insanity. Agreed. > Whether or not we try to fix these sorts of bugs submitted by security > researchers. :-) and agreed. :) --D > - Ted
