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>

diff --git a/fs/ext4/ext4_common.c b/fs/ext4/ext4_common.c
index 8a142e2e6a1868a6e9679c416f721bc7bdd414ac..5bf78b530a989108e9298f4c374f7794de10a9a5 100644 (file)
--- 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;