On Mon, Jun 18, 2018 at 11:06:52PM -0700, Darrick J. Wong wrote: > On Tue, Jun 19, 2018 at 03:27:59PM +1000, Dave Chinner wrote: > > On Mon, Jun 18, 2018 at 09:54:05PM -0700, Darrick J. Wong wrote: > > > On Tue, Jun 19, 2018 at 12:41:27PM +1000, Dave Chinner wrote: > > > > From: Dave Chinner <dchinner@xxxxxxxxxx> > > > > > > > > If we are punching out a delalloc extent, xfs_bunmapi() does not > > > > have a transaction context and should not ever need to convert the > > > > on-disk extent format. If such a thing is attempted (e.g. via a > > > > corrupt inode extent count in extent format) then we should abort > > > > with an EFSCORRUPTED error. Unfortunately, we don't do that and > > > > crash instead: > > > > > > > > XFS (loop0): page discard on page 0000000005fd24f3, inode 0x75e5, offset 0. > > > > ================================================================== > > > > BUG: KASAN: null-ptr-deref in xfs_alloc_get_freelist+0x115/0x350 > > > > Read of size 8 at addr 0000000000000028 by task a.out/1406 > > > > CPU: 0 PID: 1406 Comm: a.out Not tainted 4.17.0-rc4-kasan #2 > > > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014 > > > > Call Trace: > > > > dump_stack+0x7b/0xb5 > > > > kasan_report+0x10c/0x390 > > > > __asan_load8+0x54/0x90 > > > > xfs_alloc_get_freelist+0x115/0x350 > > > > xfs_alloc_fix_freelist+0x35b/0x830 > > > > xfs_alloc_vextent+0x215/0x990 > > > > xfs_bmap_extents_to_btree+0x30d/0x940 > > > > ..... > > > > > > > > By returning an error here, we avoid such crashes when punching out > > > > a delalloc page because we don't try to fix up an AG freelist > > > > without a transaction. Hence we get an error like so: > > > > > > Um, isn't erroring out here leaving a dirty bomb in the in-core metadata? > > > > Not that I can tell. We've already trashed the dirty page state by > > this point, so the page cache can safely reclaim the page and the > > delalloc range over it will never get written. And the XFS inode > > cleanup code didn't have any issues with the way the error was > > handled, either, because the delalloc range was actually removed > > before the fork format error was triggered. > > > > IOWs, there is no dirty, stale page state or delalloc extents > > hanging around if this error fires. > > Hmmm, well I guess I'll pull this one in and look for problems. > > I wonder, is there a <cough> testcase for this? Or a fuzz-o-matic to > turn all these things into regression tests? No test case. Should be able to create one easily enough with xfs_db, though I haven't tried. Do the inode fuzzer tests screw with the extent count? > > But OTOH, I don't want to risk a bunch of filesystem corrupting > > regressions across the entire XFS userbase just to fix a trivially > > simple crash that requires an extremely unlikely co-ordinated > > corruption of an inode data fork and an AGFL, and to simultaneously > > have ENOSPC in every other AGF in the filesystem. > > > > Put "refactor xfs_bunmapi()" on the list of "things to do when > > there's nothing else to do"... > > So in 2066 after the polar ice caps melt after the XFS LOGHAMMER attack > has finally been put down? Ok. :) I'm sure someone will have reason to factor it before then :P Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
