ext2: correct max file size computing

BugLink: https://bugs.launchpad.net/bugs/1969110
[ Upstream commit 50b3a818991074177a56c87124c7a7bdf5fa4f67 ]

We need to calculate the max file size accurately if the total blocks
that can address by block tree exceed the upper_limit. But this check is
not correct now, it only compute the total data blocks but missing
metadata blocks are needed. So in the case of "data blocks < upper_limit
&& total blocks > upper_limit", we will get wrong result. Fortunately,
this case could not happen in reality, but it's confused and better to
correct the computing.

  bits   data blocks   metadatablocks   upper_limit
  10        16843020            66051    2147483647
  11       134480396           263171    1073741823
  12      1074791436          1050627     536870911 (*)
  13      8594130956          4198403     268435455 (*)
  14     68736258060         16785411     134217727 (*)
  15    549822930956         67125251      67108863 (*)
  16   4398314962956        268468227      33554431 (*)

  [*] Need to calculate in depth.

Fixes: 1c2d14212b15 ("ext2: Fix underflow in ext2_max_size()")
Link: https://lore.kernel.org/r/20220212050532.179055-1-yi.zhang@huawei.com
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit 3813591bc046f8c4739a6be0c92acf05a1a1d729)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index d8d580b609baa2071c9c0dd6a8d14be51972fd69..3d21279fe2cb5e27e1cb08c1b66d6929786eff8a 100644 (file)
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -753,8 +753,12 @@ static loff_t ext2_max_size(int bits)
        res += 1LL << (bits-2);
        res += 1LL << (2*(bits-2));
        res += 1LL << (3*(bits-2));
+       /* Compute how many metadata blocks are needed */
+       meta_blocks = 1;
+       meta_blocks += 1 + ppb;
+       meta_blocks += 1 + ppb + ppb * ppb;
        /* Does block tree limit file size? */
-       if (res < upper_limit)
+       if (res + meta_blocks <= upper_limit)
                goto check_lfs;
 
        res = upper_limit;