ACK: [SRU][Bionic][PATCH 1/1] f2fs: fix to avoid out-of-bounds memory access

[Stefan Bader]

On 08.02.22 21:19, Joseph Salisbury wrote:
> From: Chao Yu <yuchao0 at huawei.com>
> 
> butt3rflyh4ck <butterflyhuangxx at gmail.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-and-tested-by: butt3rflyh4ck <butterflyhuangxx at gmail.com>
> Signed-off-by: Chao Yu <yuchao0 at huawei.com>
> Signed-off-by: Jaegeuk Kim <jaegeuk at kernel.org>
> (backported from commit b862676e371715456c9dade7990c8004996d0d9e)
> [jsalisbury: Preserved name of function check_nid_range() due to later commit
>   4d57b86dd86404fd8bb4f87d277d5a86a7fe537e, which changes name to
>   f2fs_check_nid_range]
> CVE-2021-3506
> Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
> ---
>   fs/f2fs/node.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index 70428dd6f797..1b1f061ea6e1 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -2406,6 +2406,9 @@ 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 (check_nid_range(sbi, nid))
> +			continue;
> +
>   		raw_ne = nat_in_journal(journal, i);
>   
>   		ne = __lookup_nat_cache(nm_i, nid);

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