From 084be43b751df7133c94c6bf556bc61bd6297406 Mon Sep 17 00:00:00 2001
From: Paul Emge <paulemge@forallsecure.com>
Date: Mon, 8 Jul 2019 16:37:06 -0700
Subject: [PATCH] ext4: gracefully fail on divide-by-0
This patch checks for 0 in several ext4 headers and gracefully
fails instead of raising a divide-by-0 exception.
Signed-off-by: Paul Emge <paulemge@forallsecure.com>
---
fs/ext4/ext4_common.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/fs/ext4/ext4_common.c b/fs/ext4/ext4_common.c
index 8a142e2e6a..5bf78b530a 100644
--- a/fs/ext4/ext4_common.c
+++ b/fs/ext4/ext4_common.c
@@ -1571,8 +1571,12 @@ static int ext4fs_blockgroup
int log2blksz = get_fs()->dev_desc->log2blksz;
int desc_size = get_fs()->gdsize;
+ if (desc_size == 0)
+ return 0;
desc_per_blk = EXT2_BLOCK_SIZE(data) / desc_size;
+ if (desc_per_blk == 0)
+ return 0;
blkno = le32_to_cpu(data->sblock.first_data_block) + 1 +
group / desc_per_blk;
blkoff = (group % desc_per_blk) * desc_size;
@@ -1602,6 +1606,10 @@ int ext4fs_read_inode(struct ext2_data *data, int ino, struct ext2_inode *inode)
/* It is easier to calculate if the first inode is 0. */
ino--;
+ if ( le32_to_cpu(sblock->inodes_per_group) == 0 || fs->inodesz == 0) {
+ free(blkgrp);
+ return 0;
+ }
status = ext4fs_blockgroup(data, ino / le32_to_cpu
(sblock->inodes_per_group), blkgrp);
if (status == 0) {
@@ -1610,6 +1618,10 @@ int ext4fs_read_inode(struct ext2_data *data, int ino, struct ext2_inode *inode)
}
inodes_per_block = EXT2_BLOCK_SIZE(data) / fs->inodesz;
+ if ( inodes_per_block == 0 ) {
+ free(blkgrp);
+ return 0;
+ }
blkno = ext4fs_bg_get_inode_table_id(blkgrp, fs) +
(ino % le32_to_cpu(sblock->inodes_per_group)) / inodes_per_block;
blkoff = (ino % inodes_per_block) * fs->inodesz;
--
2.39.5