CVE-2024-49889: Use After Free

In the Linux kernel, the following vulnerability has been resolved:

ext4: avoid use-after-free in ext4_ext_show_leaf()

In ext4_find_extent(), path may be freed by error or be reallocated, so using a previously saved *ppath may have been freed and thus may trigger use-after-free, as follows:

ext4_split_extent path = *ppath; ext4_split_extent_at(ppath) path = ext4_find_extent(ppath) ext4_split_extent_at(ppath) // ext4_find_extent fails to free path // but zeroout succeeds ext4_ext_show_leaf(inode, path) eh = path[depth].p_hdr // path use-after-free !!!

Similar to ext4_split_extent_at(), we use *ppath directly as an input to ext4_ext_show_leaf(). Fix a spelling error by the way.

Same problem in ext4_ext_handle_unwritten_extents(). Since 'path' is only used in ext4_ext_show_leaf(), remove 'path' and use *ppath directly.

This issue is triggered only when EXT_DEBUG is defined and therefore does not affect functionality.