Date: Sat, 2 Apr 2016 11:46:34 -0400 From: Theodore Ts'o <tytso@....edu> To: Yves-Alexis Perez <corsac@...ian.org> Cc: oss-security@...ts.openwall.com, Johannes Segitz <jsegitz@...e.com>, Ben Hutchings <ben@...adent.org.uk> Subject: Re: ext4 data corruption due to punch hole races On Sat, Apr 02, 2016 at 03:14:57PM +0200, Yves-Alexis Perez wrote: > > "When punching holes into a file races with the page fault of the same > > area, it is possible that freed blocks remain referenced from page cache > > pages mapped to process' address space. Thus modification of these blocks > > can corrupt data someone else is now storing in those blocks (which > > obviously has security implications if you can trick filesystem into > > storing some important file in those blocks). > > > > This affects all the kernels where we support ext4 for writing. Relevant > > fixes upstream are commits ea3d7209ca01da209cda6f0dea8be9cc4b7a933b, > > 17048e8a083fec7ad841d88ef0812707fbc7e39f, > > 32ebffd3bbb4162da5ff88f9a35dd32d0a28ea70, > > 011278485ecc3cd2a3954b5d4c73101d919bf1fa." > > any reason why those commits weren't CC: stable? If this really affects all > kernels where ext4 writing is possible, that means basically all current > stable kernels more or less, I guess? They weren't cc'ed stable because they're fairly complex patches, which (a) means they probably wouldn't auto-apply anyway, and (b) someone who does do the (probably manual) back port they would be *very* strongly advised to run them through a complete ext4 regression test series to make sure the patches actually don't make things worse from a stability perspective.  http://thunk.org/gce-xfstests I do spend *small* amount of work testing the stable kernels (3.10, 3.14, 3.18, 4.1, 4.4) using gce-xfstests and backporting and testing patches that weren't cc'ed to stable for various reasons. It's a pretty low priority task, though, and I'd really love to delegate this to someone else. I just don't have the bandwidth to support back level kernels (this is why distributions get paid the big bucks), and note that even if I or someone else stepped up, this won't necessarily help Debian, which isn't on a one of the stable kernel versions. If anyone is interested, please contact me. Otherwise, I'll get to it eventually. - Ted
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