From 592acbf16821288ecdc4192c47e3774a4c48bb64 Mon Sep 17 00:00:00 2001
From: Sriram Rajagopalan <sriramr@arista.com>
Date: Fri, 10 May 2019 19:28:06 -0400
Subject: [PATCH] ext4: zero out the unused memory region in the extent tree
 block
Git-commit: 592acbf16821288ecdc4192c47e3774a4c48bb64
Patch-mainline: v5.2-rc1
References: bsc#1135281 CVE-2019-11833

This commit zeroes out the unused memory region in the buffer_head
corresponding to the extent metablock after writing the extent header
and the corresponding extent node entries.

This is done to prevent random uninitialized data from getting into
the filesystem when the extent block is synced.

This fixes CVE-2019-11833.

Signed-off-by: Sriram Rajagopalan <sriramr@arista.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
Acked-by: Jan Kara <jack@suse.cz>

---
 fs/ext4/extents.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 0f89f5190cd7..f2c62e2a0c98 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -1035,6 +1035,7 @@ static int ext4_ext_split(handle_t *handle, struct inode *inode,
 	__le32 border;
 	ext4_fsblk_t *ablocks = NULL; /* array of allocated blocks */
 	int err = 0;
+	size_t ext_size = 0;
 
 	/* make decision: where to split? */
 	/* FIXME: now decision is simplest: at current extent */
@@ -1126,6 +1127,10 @@ static int ext4_ext_split(handle_t *handle, struct inode *inode,
 		le16_add_cpu(&neh->eh_entries, m);
 	}
 
+	/* zero out unused area in the extent block */
+	ext_size = sizeof(struct ext4_extent_header) +
+		sizeof(struct ext4_extent) * le16_to_cpu(neh->eh_entries);
+	memset(bh->b_data + ext_size, 0, inode->i_sb->s_blocksize - ext_size);
 	ext4_extent_block_csum_set(inode, neh);
 	set_buffer_uptodate(bh);
 	unlock_buffer(bh);
@@ -1205,6 +1210,11 @@ static int ext4_ext_split(handle_t *handle, struct inode *inode,
 				sizeof(struct ext4_extent_idx) * m);
 			le16_add_cpu(&neh->eh_entries, m);
 		}
+		/* zero out unused area in the extent block */
+		ext_size = sizeof(struct ext4_extent_header) +
+		   (sizeof(struct ext4_extent) * le16_to_cpu(neh->eh_entries));
+		memset(bh->b_data + ext_size, 0,
+			inode->i_sb->s_blocksize - ext_size);
 		ext4_extent_block_csum_set(inode, neh);
 		set_buffer_uptodate(bh);
 		unlock_buffer(bh);
@@ -1270,6 +1280,7 @@ static int ext4_ext_grow_indepth(handle_t *handle, struct inode *inode,
 	ext4_fsblk_t newblock, goal = 0;
 	struct ext4_super_block *es = EXT4_SB(inode->i_sb)->s_es;
 	int err = 0;
+	size_t ext_size = 0;
 
 	/* Try to prepend new index to old one */
 	if (ext_depth(inode))
@@ -1295,9 +1306,11 @@ static int ext4_ext_grow_indepth(handle_t *handle, struct inode *inode,
 		goto out;
 	}
 
+	ext_size = sizeof(EXT4_I(inode)->i_data);
 	/* move top-level index/leaf into new block */
-	memmove(bh->b_data, EXT4_I(inode)->i_data,
-		sizeof(EXT4_I(inode)->i_data));
+	memmove(bh->b_data, EXT4_I(inode)->i_data, ext_size);
+	/* zero out unused area in the extent block */
+	memset(bh->b_data + ext_size, 0, inode->i_sb->s_blocksize - ext_size);
 
 	/* set size of new block */
 	neh = ext_block_hdr(bh);
-- 
2.16.4