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

[Chao Yu <yuchao0@huawei.com>]

Hi butt3rflyh4ck,

On 2021/3/23 13:48, butt3rflyh4ck wrote:
> Hi, I have tested the patch on 5.12.0-rc4+, it seems to fix the problem.

Thanks for helping to test this patch.

Thanks,

> 
> Regards,
>   butt3rflyh4ck.
> 
> 
> On Mon, Mar 22, 2021 at 7:47 PM Chao Yu <yuchao0@huawei.com> wrote:
>>
>> butt3rflyh4ck <butterflyhuangxx@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-by: butt3rflyh4ck <butterflyhuangxx@gmail.com>
>> Signed-off-by: Chao Yu <yuchao0@huawei.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
>>
> .
>