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Subject[PATCH 1/2] f2fs: fix to avoid potential negative .f_bfree
Date
When calculating .f_bfree value in f2fs_statfs(), sbi->unusable_block_count
can be increased after the judgment condition, result in overflow of
.f_bfree in later calculation. This patch fixes to use a temporary signed
variable to save the calculation result of .f_bfree.

if (unlikely(buf->f_bfree <= sbi->unusable_block_count))
buf->f_bfree = 0;
else
buf->f_bfree -= sbi->unusable_block_count;

Signed-off-by: Chao Yu <yuchao0@huawei.com>
---
fs/f2fs/super.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 2376bb01b5c4..fcc9793dbc2c 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -1216,6 +1216,7 @@ static int f2fs_statfs(struct dentry *dentry, struct kstatfs *buf)
u64 id = huge_encode_dev(sb->s_bdev->bd_dev);
block_t total_count, user_block_count, start_count;
u64 avail_node_count;
+ long long bfree;

total_count = le64_to_cpu(sbi->raw_super->block_count);
user_block_count = sbi->user_block_count;
@@ -1226,10 +1227,12 @@ static int f2fs_statfs(struct dentry *dentry, struct kstatfs *buf)
buf->f_blocks = total_count - start_count;
buf->f_bfree = user_block_count - valid_user_blocks(sbi) -
sbi->current_reserved_blocks;
- if (unlikely(buf->f_bfree <= sbi->unusable_block_count))
+
+ bfree = buf->f_bfree - sbi->unusable_block_count;
+ if (unlikely(bfree < 0))
buf->f_bfree = 0;
else
- buf->f_bfree -= sbi->unusable_block_count;
+ buf->f_bfree = bfree;

if (buf->f_bfree > F2FS_OPTION(sbi).root_reserved_blocks)
buf->f_bavail = buf->f_bfree -
--
2.18.0.rc1
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