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? (Yeah, I know there won't be one for syzbot, I dug through its code and had to reset my brain by reading mballoc.c. :P) > > Like you say: > > > > > XFS (loop0): page discard on page ffffea00040ae640, inode 0x75e5, offset 0. > > > XFS (loop0): page discard unable to remove delalloc mapping. > > > > We know the fs is corrupt, we might as well shut down now rather than > > let this burp out later. > > xfs_bunmapi() doesn't do shutdowns - the higher level code does a > shutdown on error if it is necessary, otherwise it just propagates > the error. In this case it has cleaned up correctly, propagates the > error and it gets back to userspace on the next fsync, and we're > fine to continue onwards as there was no unrecoverable error.... Fair enough. > > I get that people don't want to touch well seasoned code, but > > xfs_bunmapi is this big unwieldly function that's crying out for a > > refactor. It's 330 lines long and can be called from various contexts > > (data/attr fork, punch delalloc, etc.)... > > > > ...it's also weird that xfs_bmap_punch_delalloc_range calls xfs_bunmapi > > with no transaction and a xfs_defer that we dump on the ground. > > Yes, and yes. > > > So yes, I think the patch does fix the crash, but it's kinda gross. > > Yes, it is. > > 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. :) (But no, seriously, if anyone's looking for a little refactoring + domain knowledge enhancement of the bmapi code...) --D > 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 -- 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
