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.



On Mon, Mar 22, 2021 at 7:47 PM Chao Yu <yuch...@huawei.com> wrote:

butt3rflyh4ck <butterflyhuan...@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.


Reported-by: butt3rflyh4ck <butterflyhuan...@gmail.com>
Signed-off-by: Chao Yu <yuch...@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 
                 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);


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