[PATCH 3.12 37/86] ext4: fix inode checksum calculation problem if i_extra_size is small

From: Jiri Slaby
Date: Thu May 04 2017 - 05:19:17 EST

From: Daeho Jeong <daeho.jeong@xxxxxxxxxxx>

3.12-stable review patch. If anyone has any objections, please let me know.


commit 05ac5aa18abd7db341e54df4ae2b4c98ea0e43b7 upstream.

We've fixed the race condition problem in calculating ext4 checksum
value in commit b47820edd163 ("ext4: avoid modifying checksum fields
directly during checksum veficationon"). However, by this change,
when calculating the checksum value of inode whose i_extra_size is
less than 4, we couldn't calculate the checksum value in a proper way.
This problem was found and reported by Nix, Thank you.

Reported-by: Nix <nix@xxxxxxxxxxxxx>
Signed-off-by: Daeho Jeong <daeho.jeong@xxxxxxxxxxx>
Signed-off-by: Youngjin Gil <youngjin.gil@xxxxxxxxxxx>
Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
fs/ext4/inode.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 50fc2d1da9a9..9a3e7cffd6eb 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -73,10 +73,9 @@ static __u32 ext4_inode_csum(struct inode *inode, struct ext4_inode *raw,
csum = ext4_chksum(sbi, csum, (__u8 *)&dummy_csum,
offset += csum_size;
- csum = ext4_chksum(sbi, csum, (__u8 *)raw + offset,
- EXT4_INODE_SIZE(inode->i_sb) -
- offset);
+ csum = ext4_chksum(sbi, csum, (__u8 *)raw + offset,
+ EXT4_INODE_SIZE(inode->i_sb) - offset);

return csum;