[PATCH 5.16 0548/1017] ext2: correct max file size computing

Greg Kroah-Hartman
2022-04-05T12:53:07Z

From: Zhang Yi <yi.zhang@huawei.com>

[ 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>
---
fs/ext2/super.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index d8d580b609ba..3d21279fe2cb 100644
--- 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;
--
2.34.1