[syzbot] [erofs?] KMSAN: uninit-value in erofs_fc_fill_super

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 9b2ffa6148b1 Merge tag 'mtd/fixes-for-6.13-rc5' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=112374c4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f9048090d7bb0d06
dashboard link: https://syzkaller.appspot.com/bug?extid=1379ee6b9a14d5dacaf2
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/244f25c1a275/disk-9b2ffa61.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0d14fc6634fd/vmlinux-9b2ffa61.xz
kernel image: https://storage.googleapis.com/syzbot-assets/cb152a4c0fd2/bzImage-9b2ffa61.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1379ee...@syzkaller.appspotmail.com

exFAT-fs (loop7): failed to load upcase table (idx : 0x00010000, chksum : 0x1a9973fb, utbl_chksum : 0xe619d30d)
=====================================================
BUG: KMSAN: uninit-value in erofs_read_superblock fs/erofs/super.c:274 [inline]
BUG: KMSAN: uninit-value in erofs_fc_fill_super+0x66a/0x2520 fs/erofs/super.c:614
erofs_read_superblock fs/erofs/super.c:274 [inline]
erofs_fc_fill_super+0x66a/0x2520 fs/erofs/super.c:614
vfs_get_super fs/super.c:1280 [inline]
get_tree_nodev+0x183/0x350 fs/super.c:1299
erofs_fc_get_tree+0x34d/0x450 fs/erofs/super.c:721
vfs_get_tree+0xb1/0x5a0 fs/super.c:1814
do_new_mount+0x71f/0x15e0 fs/namespace.c:3507
path_mount+0x742/0x1f10 fs/namespace.c:3834
do_mount fs/namespace.c:3847 [inline]
__do_sys_mount fs/namespace.c:4057 [inline]
__se_sys_mount+0x722/0x810 fs/namespace.c:4034
__x64_sys_mount+0xe4/0x150 fs/namespace.c:4034
x64_sys_call+0x39bf/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:166
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:
__alloc_pages_noprof+0x9a7/0xe00 mm/page_alloc.c:4776
alloc_pages_mpol_noprof+0x299/0x990 mm/mempolicy.c:2269
alloc_pages_noprof mm/mempolicy.c:2348 [inline]
folio_alloc_noprof+0x1db/0x310 mm/mempolicy.c:2355
filemap_alloc_folio_noprof+0xa6/0x440 mm/filemap.c:1009
__filemap_get_folio+0xac4/0x1550 mm/filemap.c:1951
block_write_begin+0x6e/0x2b0 fs/buffer.c:2221
exfat_write_begin+0xfb/0x400 fs/exfat/inode.c:434
exfat_extend_valid_size fs/exfat/file.c:553 [inline]
exfat_file_write_iter+0x771/0x12a0 fs/exfat/file.c:598
do_iter_readv_writev+0x88a/0xa30
vfs_writev+0x56a/0x14f0 fs/read_write.c:1050
do_pwritev fs/read_write.c:1146 [inline]
__do_sys_pwritev2 fs/read_write.c:1204 [inline]
__se_sys_pwritev2+0x262/0x460 fs/read_write.c:1195
__x64_sys_pwritev2+0x11f/0x1a0 fs/read_write.c:1195
x64_sys_call+0x368c/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:329
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

CPU: 1 UID: 0 PID: 8448 Comm: syz.7.643 Not tainted 6.13.0-rc4-syzkaller-00012-g9b2ffa6148b1 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
=====================================================


---
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 syzk...@googlegroups.com.

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

[Namjae Jeon]

On Mon, Dec 30, 2024 at 11:53 AM Gao Xiang <xi...@kernel.org> wrote:
>
> Hi exfat maintainers,
Hi Gao,

We have a patch for this and will send a PR to Linus soon.
Thanks!

> Currently, I don't think it's an EROFS issue but since it doesn't have
> a valid reproducer so I don't have an exact idea.
>
> This case is out of EROFS file-backed mount, which seems to read EROFS
> superblock (erofs_read_superblock -> erofs_read_metabuf -> erofs_bread)
> via exfat page cache:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/erofs/super.c?h=v6.13-rc5#n274
>
> But it seems exfat returns an unlocked uptodate page without fully
> initialized data.
>
> I'm not sure if it's a post-EOF read for this specific regular inode,
> but IMHO, at least mmap read allows post-EOF read within the same page,
> so it'd be better to leave the whole page initialized on the exfat side.
>
> I'm not sure if it's related to exfat_extend_valid_size() though.
>
> Thanks,
> Gao Xiang

[Gao Xiang]

Hi Namjae,

On 2024/12/30 12:33, Namjae Jeon via Linux-erofs wrote:
> On Mon, Dec 30, 2024 at 11:53 AM Gao Xiang <xi...@kernel.org> wrote:
>>
>> Hi exfat maintainers,
> Hi Gao,
>
> We have a patch for this and will send a PR to Linus soon.
> Thanks!

Many thanks! So good to hear that. Also (just friendly in
case) it would be helpful to add the following reported-by
to close this syzbot issue..

Anyway, if addresses at the exfat side:
#syz set subsystems: exfat

Thanks,
Gao Xiang

[Gao Xiang]

Hi exfat maintainers,

On Sat, Dec 28, 2024 at 11:45:22PM -0800, syzbot wrote:

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.