linux-kernel - Re: [syzbot] [erofs?] KMSAN: uninit-value in erofs_fc_fill

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Message-ID: <CAKYAXd-wg9dMsv_UgUKVeLCqkFjroh3mBUcywE8mvDcFasjNwA@mail.gmail.com>
Date: Mon, 30 Dec 2024 13:33:58 +0900
From: Namjae Jeon <linkinjeon@...nel.org>
To: Namjae Jeon <linkinjeon@...nel.org>, Sungjong Seo <sj1557.seo@...sung.com>, 
	Yuezhang Mo <yuezhang.mo@...y.com>, 
	syzbot <syzbot+1379ee6b9a14d5dacaf2@...kaller.appspotmail.com>, 
	linux-erofs@...ts.ozlabs.org, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [erofs?] KMSAN: uninit-value in erofs_fc_fill_super

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

We have a patch for this and will send a PR to Linus soon.
Thanks!
>
> On Sat, Dec 28, 2024 at 11:45:22PM -0800, syzbot wrote:
> > 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+1379ee6b9a14d5dacaf2@...kaller.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
> >
>
> 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