[PATCH 5.12 050/700] ext4: fix kernel infoleak via ext4_extent_header

[Greg Kroah-Hartman]

From: Anirudh Rayabharam <mail@xxxxxxxxxxxxx>

commit ce3aba43599f0b50adbebff133df8d08a3d5fffe upstream.

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

Cc: stable@xxxxxxxxxx
Reported-by: syzbot+2dcfeaf8cb49b05e8f1a@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: a86c61812637 ("[PATCH] ext3: add extent map support")
Signed-off-by: Anirudh Rayabharam <mail@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210506185655.7118-1-mail@xxxxxxxxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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

--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -825,6 +825,7 @@ void ext4_ext_tree_init(handle_t *handle
 	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 *hand
 	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 *hand
 		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);