These are all the ext4 patches that were tagged for -stable and failed to apply to 3.18.y.
Patch e40ff2138985 ("ext4: force revalidation of directory pointer after seekdir(2)") was Cc'd to stable as well but it requires commmit ae5e165d855d ("fs: new API for handling inode->i_version") to be applied as well which is neither a stable candidate nor under 100 lines so I've skipped e40ff2138985. If somebody can suggest a backport of the commit which doesn't require ae5e165d855d, I'll be glad.
Theodore Ts'o (3): ext4: add validity checks for bitmap block numbers ext4: fail ext4_iget for root directory if unallocated ext4: don't allow r/w mounts if metadata blocks overlap the superblock
fs/ext4/balloc.c | 16 ++++++++++++++-- fs/ext4/ialloc.c | 8 +++++++- fs/ext4/inode.c | 6 ++++++ fs/ext4/super.c | 6 ++++++ 4 files changed, 33 insertions(+), 3 deletions(-)