Re: [syzbot] [bcachefs?] KMSAN: uninit-value in bch2_extent_update_i_size_sectors

From: Alexander Potapenko
Date: Thu May 23 2024 - 04:16:53 EST

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In reply to: Kent Overstreet: "Re: [syzbot] [bcachefs?] KMSAN: uninit-value in bch2_extent_update_i_size_sectors"
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On Thu, May 23, 2024 at 1:49 AM Kent Overstreet
<kent.overstreet@xxxxxxxxx> wrote:
>
> This (and a few others I've looked at) look more likely to be bugs in
> KMSAN, not bcachefs.

Yeah, this is possible if we are missing some initialization.

>
> here, the supposedly uninitialized key was read in from disk, so the key
> couldn't possibly have been legitimately marked uninitialized.

Am I right that the key is supposed to be initialized before the first
call of memcpy_u64s_small() (the _lower_ "Uninit was stored to memory
at:" stack trace)?
Do you have an idea what code performed the actual load of the data from disk?
If that load was done by some assembly routine, we could've easily
missed that - in that case we'll need to annotate it to fix the false
positives.

>
> All the suspicious KMSAN splats I'm looking at involve bkeys, but I'm
> not seeing any other common factors besides that.
>
> On Sat, May 11, 2024 at 01:52:29PM -0700, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit: dccb07f2914c Merge tag 'for-6.9-rc7-tag' of git://git.kern..
> > git tree: upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=14c66e24980000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=617171361dd3cd47
> > dashboard link: https://syzkaller.appspot.com/bug?extid=eceea46e8838baeeba67
> > compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> >
> > Unfortunately, I don't have any reproducer for this issue yet.
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/fdbc7be30633/disk-dccb07f2.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/a9e4c11aa835/vmlinux-dccb07f2.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/43c3a343ea93/bzImage-dccb07f2.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+eceea46e8838baeeba67@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > bcachefs (loop0): snapshots_read... done
> > bcachefs (loop0): journal_replay... done
> > bcachefs (loop0): resume_logged_ops... done
> > bcachefs (loop0): going read-write
> > bcachefs (loop0): done starting filesystem
> > =====================================================
> > BUG: KMSAN: uninit-value in bch2_extent_update_i_size_sectors+0x140f/0x17d0 fs/bcachefs/io_write.c:237
> > bch2_extent_update_i_size_sectors+0x140f/0x17d0 fs/bcachefs/io_write.c:237
> > bch2_extent_update+0x4f5/0xac0 fs/bcachefs/io_write.c:314
> > bch2_write_index_default fs/bcachefs/io_write.c:366 [inline]
> > __bch2_write_index+0x1653/0x2bd0 fs/bcachefs/io_write.c:520
> > bch2_write_data_inline fs/bcachefs/io_write.c:1538 [inline]
> > bch2_write+0x1a13/0x1b40 fs/bcachefs/io_write.c:1606
> > closure_queue include/linux/closure.h:257 [inline]
> > closure_call include/linux/closure.h:390 [inline]
> > bch2_writepage_do_io fs/bcachefs/fs-io-buffered.c:468 [inline]
> > bch2_writepages+0x24a/0x3c0 fs/bcachefs/fs-io-buffered.c:660
> > do_writepages+0x427/0xc30 mm/page-writeback.c:2612
> > filemap_fdatawrite_wbc+0x1d8/0x270 mm/filemap.c:397
> > __filemap_fdatawrite_range+0xe3/0x120 mm/filemap.c:430
> > sync_file_range+0x316/0x450 fs/sync.c:292
> > ksys_sync_file_range fs/sync.c:364 [inline]
> > __do_sys_sync_file_range fs/sync.c:373 [inline]
> > __se_sys_sync_file_range fs/sync.c:370 [inline]
> > __x64_sys_sync_file_range+0x15a/0x2a0 fs/sync.c:370
> > x64_sys_call+0xc90/0x3b50 arch/x86/include/generated/asm/syscalls_64.h:278
> > do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> > do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
> > entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >
> > Uninit was stored to memory at:
> > memcpy_u64s_small fs/bcachefs/util.h:511 [inline]
> > bkey_reassemble fs/bcachefs/bkey.h:505 [inline]
> > __bch2_bkey_make_mut_noupdate fs/bcachefs/btree_update.h:225 [inline]
> > __bch2_bkey_get_mut_noupdate fs/bcachefs/btree_update.h:282 [inline]
> > bch2_bkey_get_mut_noupdate fs/bcachefs/btree_update.h:293 [inline]
> > bch2_extent_update_i_size_sectors+0x9a9/0x17d0 fs/bcachefs/io_write.c:219
> > bch2_extent_update+0x4f5/0xac0 fs/bcachefs/io_write.c:314
> > bch2_write_index_default fs/bcachefs/io_write.c:366 [inline]
> > __bch2_write_index+0x1653/0x2bd0 fs/bcachefs/io_write.c:520
> > bch2_write_data_inline fs/bcachefs/io_write.c:1538 [inline]
> > bch2_write+0x1a13/0x1b40 fs/bcachefs/io_write.c:1606
> > closure_queue include/linux/closure.h:257 [inline]
> > closure_call include/linux/closure.h:390 [inline]
> > bch2_writepage_do_io fs/bcachefs/fs-io-buffered.c:468 [inline]
> > bch2_writepages+0x24a/0x3c0 fs/bcachefs/fs-io-buffered.c:660
> > do_writepages+0x427/0xc30 mm/page-writeback.c:2612
> > filemap_fdatawrite_wbc+0x1d8/0x270 mm/filemap.c:397
> > __filemap_fdatawrite_range+0xe3/0x120 mm/filemap.c:430
> > sync_file_range+0x316/0x450 fs/sync.c:292
> > ksys_sync_file_range fs/sync.c:364 [inline]
> > __do_sys_sync_file_range fs/sync.c:373 [inline]
> > __se_sys_sync_file_range fs/sync.c:370 [inline]
> > __x64_sys_sync_file_range+0x15a/0x2a0 fs/sync.c:370
> > x64_sys_call+0xc90/0x3b50 arch/x86/include/generated/asm/syscalls_64.h:278
> > do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> > do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
> > entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >
> > Uninit was stored to memory at:
> > memcpy_u64s_small fs/bcachefs/util.h:511 [inline]
> > bkey_reassemble fs/bcachefs/bkey.h:505 [inline]
> > btree_key_cache_fill fs/bcachefs/btree_key_cache.c:454 [inline]
> > bch2_btree_path_traverse_cached_slowpath+0x5f02/0x79f0 fs/bcachefs/btree_key_cache.c:530
> > bch2_btree_path_traverse_cached+0xd1a/0x1140
> > bch2_btree_path_traverse_one+0x737/0x5290 fs/bcachefs/btree_iter.c:1155
> > bch2_btree_path_traverse fs/bcachefs/btree_iter.h:225 [inline]
> > bch2_btree_iter_peek_slot+0x128c/0x3840 fs/bcachefs/btree_iter.c:2473
> > __bch2_bkey_get_iter fs/bcachefs/btree_iter.h:549 [inline]
> > __bch2_bkey_get_mut_noupdate fs/bcachefs/btree_update.h:278 [inline]
> > bch2_bkey_get_mut_noupdate fs/bcachefs/btree_update.h:293 [inline]
> > bch2_extent_update_i_size_sectors+0x404/0x17d0 fs/bcachefs/io_write.c:219
> > bch2_extent_update+0x4f5/0xac0 fs/bcachefs/io_write.c:314
> > bch2_write_index_default fs/bcachefs/io_write.c:366 [inline]
> > __bch2_write_index+0x1653/0x2bd0 fs/bcachefs/io_write.c:520
> > bch2_write_data_inline fs/bcachefs/io_write.c:1538 [inline]
> > bch2_write+0x1a13/0x1b40 fs/bcachefs/io_write.c:1606
> > closure_queue include/linux/closure.h:257 [inline]
> > closure_call include/linux/closure.h:390 [inline]
> > bch2_writepage_do_io fs/bcachefs/fs-io-buffered.c:468 [inline]
> > bch2_writepages+0x24a/0x3c0 fs/bcachefs/fs-io-buffered.c:660
> > do_writepages+0x427/0xc30 mm/page-writeback.c:2612
> > filemap_fdatawrite_wbc+0x1d8/0x270 mm/filemap.c:397
> > __filemap_fdatawrite_range+0xe3/0x120 mm/filemap.c:430
> > sync_file_range+0x316/0x450 fs/sync.c:292
> > ksys_sync_file_range fs/sync.c:364 [inline]
> > __do_sys_sync_file_range fs/sync.c:373 [inline]
> > __se_sys_sync_file_range fs/sync.c:370 [inline]
> > __x64_sys_sync_file_range+0x15a/0x2a0 fs/sync.c:370
> > x64_sys_call+0xc90/0x3b50 arch/x86/include/generated/asm/syscalls_64.h:278
> > do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> > do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
> > entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >
> > Uninit was created at:
> > __kmalloc_large_node+0x231/0x370 mm/slub.c:3927
> > __do_kmalloc_node mm/slub.c:3960 [inline]
> > __kmalloc_node+0xb10/0x10c0 mm/slub.c:3979
> > kmalloc_node include/linux/slab.h:648 [inline]
> > kvmalloc_node+0xc0/0x2d0 mm/util.c:634
> > kvmalloc include/linux/slab.h:766 [inline]
> > btree_bounce_alloc fs/bcachefs/btree_io.c:118 [inline]
> > bch2_btree_node_read_done+0x4e68/0x75e0 fs/bcachefs/btree_io.c:1185
> > btree_node_read_work+0x8a5/0x1eb0 fs/bcachefs/btree_io.c:1324
> > bch2_btree_node_read+0x3d42/0x4b50
> > __bch2_btree_root_read fs/bcachefs/btree_io.c:1748 [inline]
> > bch2_btree_root_read+0xa6c/0x13d0 fs/bcachefs/btree_io.c:1772
> > read_btree_roots+0x454/0xee0 fs/bcachefs/recovery.c:457
> > bch2_fs_recovery+0x7adb/0x9310 fs/bcachefs/recovery.c:785
> > bch2_fs_start+0x7b2/0xbd0 fs/bcachefs/super.c:1043
> > bch2_fs_open+0x135f/0x1670 fs/bcachefs/super.c:2102
> > bch2_mount+0x90d/0x1d90 fs/bcachefs/fs.c:1903
> > legacy_get_tree+0x114/0x290 fs/fs_context.c:662
> > vfs_get_tree+0xa7/0x570 fs/super.c:1779
> > do_new_mount+0x71f/0x15e0 fs/namespace.c:3352
> > path_mount+0x742/0x1f20 fs/namespace.c:3679
> > do_mount fs/namespace.c:3692 [inline]
> > __do_sys_mount fs/namespace.c:3898 [inline]
> > __se_sys_mount+0x725/0x810 fs/namespace.c:3875
> > __x64_sys_mount+0xe4/0x150 fs/namespace.c:3875
> > x64_sys_call+0x2bf4/0x3b50 arch/x86/include/generated/asm/syscalls_64.h:166
> > do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> > do_syscall_64+0xcf/0x1e0 arch/x86/entry/common.c:83
> > entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >
> > CPU: 1 PID: 6218 Comm: syz-executor.0 Not tainted 6.9.0-rc7-syzkaller-00012-gdccb07f2914c #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
> > =====================================================
> >
> >
> > ---
> > This report is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.
> >
> > syzbot will keep track of this issue. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> >
> > If the report is already addressed, let syzbot know by replying with:
> > #syz fix: exact-commit-title
> >
> > If you want to overwrite report's subsystems, reply with:
> > #syz set subsystems: new-subsystem
> > (See the list of subsystem names on the web dashboard)
> >
> > If the report is a duplicate of another one, reply with:
> > #syz dup: exact-subject-of-another-report
> >
> > If you want to undo deduplication, reply with:
> > #syz undup

--
Alexander Potapenko
Software Engineer

Google Germany GmbH
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80636 München

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In reply to: Kent Overstreet: "Re: [syzbot] [bcachefs?] KMSAN: uninit-value in bch2_extent_update_i_size_sectors"
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