Re: [syzbot] [nilfs?] KMSAN: uninit-value in nilfs_add_checksums_on_logs (3)

[Ryusuke Konishi]

On Sun, Jun 16, 2024 at 8:03 AM Ryusuke Konishi wrote:
>
> On Sun, Jun 16, 2024 at 4:43 AM syzbot wrote:
> >
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    614da38e2f7a Merge tag 'hid-for-linus-2024051401' of git:/..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=12d26ada980000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=f5d2cbf33633f507
> > dashboard link: https://syzkaller.appspot.com/bug?extid=206133fb2e7b32bba4be
> > 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/89eafb874b71/disk-614da38e.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/356000512ad9/vmlinux-614da38e.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/839c73939115/bzImage-614da38e.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+206133fb2e7b32bba4be@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > =====================================================
> > BUG: KMSAN: uninit-value in crc32_body lib/crc32.c:110 [inline]
> > BUG: KMSAN: uninit-value in crc32_le_generic lib/crc32.c:179 [inline]
> > BUG: KMSAN: uninit-value in crc32_le_base+0x43c/0xd80 lib/crc32.c:197
> >  crc32_body lib/crc32.c:110 [inline]
> >  crc32_le_generic lib/crc32.c:179 [inline]
> >  crc32_le_base+0x43c/0xd80 lib/crc32.c:197
> >  nilfs_segbuf_fill_in_data_crc fs/nilfs2/segbuf.c:224 [inline]
> >  nilfs_add_checksums_on_logs+0xb80/0xe40 fs/nilfs2/segbuf.c:327
> >  nilfs_segctor_do_construct+0x9876/0xdeb0 fs/nilfs2/segment.c:2078
> >  nilfs_segctor_construct+0x1eb/0xe30 fs/nilfs2/segment.c:2381
> >  nilfs_segctor_thread_construct fs/nilfs2/segment.c:2489 [inline]
> >  nilfs_segctor_thread+0xc50/0x11e0 fs/nilfs2/segment.c:2573
> >  kthread+0x3e2/0x540 kernel/kthread.c:389
> >  ret_from_fork+0x6d/0x90 arch/x86/kernel/process.c:147
> >  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> >
> > Uninit was stored to memory at:
> >  memcpy_from_iter lib/iov_iter.c:73 [inline]
> >  iterate_bvec include/linux/iov_iter.h:122 [inline]
> >  iterate_and_advance2 include/linux/iov_iter.h:249 [inline]
> >  iterate_and_advance include/linux/iov_iter.h:271 [inline]
> >  __copy_from_iter lib/iov_iter.c:249 [inline]
> >  copy_page_from_iter_atomic+0x12b7/0x2ae0 lib/iov_iter.c:481
> >  generic_perform_write+0x4c1/0xc60 mm/filemap.c:3982
> >  __generic_file_write_iter+0x20a/0x460 mm/filemap.c:4069
> >  generic_file_write_iter+0x103/0x5b0 mm/filemap.c:4095
> >  __kernel_write_iter+0x64d/0xc80 fs/read_write.c:523
> >  dump_emit_page fs/coredump.c:895 [inline]
> >  dump_user_range+0x8dc/0xee0 fs/coredump.c:956
> >  elf_core_dump+0x57c7/0x5ae0 fs/binfmt_elf.c:2083
> >  do_coredump+0x32d5/0x4920 fs/coredump.c:769
> >  get_signal+0x267e/0x2d00 kernel/signal.c:2896
> >  arch_do_signal_or_restart+0x53/0xcb0 arch/x86/kernel/signal.c:310
> >  exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
> >  exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
> >  __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
> >  syscall_exit_to_user_mode+0x5d/0x160 kernel/entry/common.c:218
> >  do_syscall_64+0xdc/0x1e0 arch/x86/entry/common.c:89
> >  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >
> > Uninit was created at:
> >  __alloc_pages+0x9d6/0xe70 mm/page_alloc.c:4598
> >  alloc_pages_mpol+0x299/0x990 mm/mempolicy.c:2264
> >  alloc_pages+0x1bf/0x1e0 mm/mempolicy.c:2335
> >  dump_user_range+0x4a/0xee0 fs/coredump.c:940
> >  elf_core_dump+0x57c7/0x5ae0 fs/binfmt_elf.c:2083
> >  do_coredump+0x32d5/0x4920 fs/coredump.c:769
> >  get_signal+0x267e/0x2d00 kernel/signal.c:2896
> >  arch_do_signal_or_restart+0x53/0xcb0 arch/x86/kernel/signal.c:310
> >  exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
> >  exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
> >  __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
> >  syscall_exit_to_user_mode+0x5d/0x160 kernel/entry/common.c:218
> >  do_syscall_64+0xdc/0x1e0 arch/x86/entry/common.c:89
> >  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >
> > CPU: 0 PID: 5368 Comm: segctord Not tainted 6.9.0-syzkaller-02707-g614da38e2f7a #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
> > =====================================================
> >
> >
> > ---
> > 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
>
> Ah, this issue appears to be the same as the following issue where a
> memory dump generated by elf_core_dump() gets mixed into the
> filesystem:
>
> https://syzkaller.appspot.com/bug?extid=47a017c46edb25eff048
>
> However, the kernel that syzbot tested had the common fix for this
> issue, commit 61b258b0d2f6 ("x86: call instrumentation hooks from
> copy_mc.c") applied.  So the patch may not have fixed the issue.
>
> Ryusuke Konishi

#syz dup: KMSAN: uninit-value in nilfs_add_checksums_on_logs (2)

After checking again, I found that the fix for this issue, commit
61b258b0d2f6 ("x86: call instrumentation hooks from copy_mc.c"), had
not yet been applied to the kernel of commit 614da38e2f7a, for which
the problem was reported.

My initial analysis above was incorrect; this issue overlaps with the
existing bug that has already been fixed.

Ryusuke Konishi