[PATCH v2] ext4: fix kernel infoleak via ext4_extent_header

[Anirudh Rayabharam]

Initialize eh_generation of struct ext4_extent_header to prevent leaking
info to userspace. Fixes KMSAN kernel-infoleak bug reported by syzbot at:
http://syzkaller.appspot.com/bug?id=78e9ad0e6952a3ca16e8234724b2fa92d041b9b8

Reported-by: syzbot+2dcfeaf8cb49b05e8f1a@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: a86c61812637 ("[PATCH] ext3: add extent map support")
Signed-off-by: Anirudh Rayabharam <mail@xxxxxxxxxxxxx>
---

Changes in v2:
Added a "Fixes:" tag.

v1: https://lore.kernel.org/lkml/20210505133011.32484-1-mail@xxxxxxxxxxxxx/

---
 fs/ext4/extents.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 77c84d6f1af6..677d4821bcc1 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -825,6 +825,7 @@ void ext4_ext_tree_init(handle_t *handle, struct inode *inode)
 	eh->eh_entries = 0;
 	eh->eh_magic = EXT4_EXT_MAGIC;
 	eh->eh_max = cpu_to_le16(ext4_ext_space_root(inode, 0));
+	eh->eh_generation = 0;
 	ext4_mark_inode_dirty(handle, inode);
 }
 
@@ -1090,6 +1091,7 @@ static int ext4_ext_split(handle_t *handle, struct inode *inode,
 	neh->eh_max = cpu_to_le16(ext4_ext_space_block(inode, 0));
 	neh->eh_magic = EXT4_EXT_MAGIC;
 	neh->eh_depth = 0;
+	neh->eh_generation = 0;
 
 	/* move remainder of path[depth] to the new leaf */
 	if (unlikely(path[depth].p_hdr->eh_entries !=
@@ -1167,6 +1169,7 @@ static int ext4_ext_split(handle_t *handle, struct inode *inode,
 		neh->eh_magic = EXT4_EXT_MAGIC;
 		neh->eh_max = cpu_to_le16(ext4_ext_space_block_idx(inode, 0));
 		neh->eh_depth = cpu_to_le16(depth - i);
+		neh->eh_generation = 0;
 		fidx = EXT_FIRST_INDEX(neh);
 		fidx->ei_block = border;
 		ext4_idx_store_pblock(fidx, oldblock);
-- 
2.26.2