linux-kernel - Re: [PATCH] f2fs: fix to avoid out-of-bounds memory access

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Date:   Tue, 23 Mar 2021 13:48:26 +0800
From:   butt3rflyh4ck <butterflyhuangxx@...il.com>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     jaegeuk@...nel.org, linux-f2fs-devel@...ts.sourceforge.net,
        LKML <linux-kernel@...r.kernel.org>, chao@...nel.org
Subject: Re: [PATCH] f2fs: fix to avoid out-of-bounds memory access

Hi, I have tested the patch on 5.12.0-rc4+, it seems to fix the problem.

Regards,
 butt3rflyh4ck.


On Mon, Mar 22, 2021 at 7:47 PM Chao Yu <yuchao0@...wei.com> wrote:
>
> butt3rflyh4ck <butterflyhuangxx@...il.com> reported a bug found by
> syzkaller fuzzer with custom modifications in 5.12.0-rc3+ [1]:
>
>  dump_stack+0xfa/0x151 lib/dump_stack.c:120
>  print_address_description.constprop.0.cold+0x82/0x32c mm/kasan/report.c:232
>  __kasan_report mm/kasan/report.c:399 [inline]
>  kasan_report.cold+0x7c/0xd8 mm/kasan/report.c:416
>  f2fs_test_bit fs/f2fs/f2fs.h:2572 [inline]
>  current_nat_addr fs/f2fs/node.h:213 [inline]
>  get_next_nat_page fs/f2fs/node.c:123 [inline]
>  __flush_nat_entry_set fs/f2fs/node.c:2888 [inline]
>  f2fs_flush_nat_entries+0x258e/0x2960 fs/f2fs/node.c:2991
>  f2fs_write_checkpoint+0x1372/0x6a70 fs/f2fs/checkpoint.c:1640
>  f2fs_issue_checkpoint+0x149/0x410 fs/f2fs/checkpoint.c:1807
>  f2fs_sync_fs+0x20f/0x420 fs/f2fs/super.c:1454
>  __sync_filesystem fs/sync.c:39 [inline]
>  sync_filesystem fs/sync.c:67 [inline]
>  sync_filesystem+0x1b5/0x260 fs/sync.c:48
>  generic_shutdown_super+0x70/0x370 fs/super.c:448
>  kill_block_super+0x97/0xf0 fs/super.c:1394
>
> The root cause is, if nat entry in checkpoint journal area is corrupted,
> e.g. nid of journalled nat entry exceeds max nid value, during checkpoint,
> once it tries to flush nat journal to NAT area, get_next_nat_page() may
> access out-of-bounds memory on nat_bitmap due to it uses wrong nid value
> as bitmap offset.
>
> [1] https://lore.kernel.org/lkml/CAFcO6XOMWdr8pObek6eN6-fs58KG9doRFadgJj-FnF-1x43s2g@mail.gmail.com/T/#u
>
> Reported-by: butt3rflyh4ck <butterflyhuangxx@...il.com>
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
>  fs/f2fs/node.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index caf43970510e..8311b2367c7c 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -2790,6 +2790,9 @@ static void remove_nats_in_journal(struct f2fs_sb_info *sbi)
>                 struct f2fs_nat_entry raw_ne;
>                 nid_t nid = le32_to_cpu(nid_in_journal(journal, i));
>
> +               if (f2fs_check_nid_range(sbi, nid))
> +                       continue;
> +
>                 raw_ne = nat_in_journal(journal, i);
>
>                 ne = __lookup_nat_cache(nm_i, nid);
> --
> 2.29.2
>