4.17-stable review patch. If anyone has any objections, please let me know.
------------------
From: Al Viro viro@zeniv.linux.org.uk
commit 4c0d7cd5c8416b1ef41534d19163cb07ffaa03ab upstream.
RCU pathwalk relies upon the assumption that anything that changes ->d_inode of a dentry will invalidate its ->d_seq. That's almost true - the one exception is that the final dput() of already unhashed dentry does *not* touch ->d_seq at all. Unhashing does, though, so for anything we'd found by RCU dcache lookup we are fine. Unfortunately, we can *start* with an unhashed dentry or jump into it.
We could try and be careful in the (few) places where that could happen. Or we could just make the final dput() invalidate the damn thing, unhashed or not. The latter is much simpler and easier to backport, so let's do it that way.
Reported-by: "Dae R. Jeong" threeearcat@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Al Viro viro@zeniv.linux.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/dcache.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-)
--- a/fs/dcache.c +++ b/fs/dcache.c @@ -358,14 +358,11 @@ static void dentry_unlink_inode(struct d __releases(dentry->d_inode->i_lock) { struct inode *inode = dentry->d_inode; - bool hashed = !d_unhashed(dentry);
- if (hashed) - raw_write_seqcount_begin(&dentry->d_seq); + raw_write_seqcount_begin(&dentry->d_seq); __d_clear_type_and_inode(dentry); hlist_del_init(&dentry->d_u.d_alias); - if (hashed) - raw_write_seqcount_end(&dentry->d_seq); + raw_write_seqcount_end(&dentry->d_seq); spin_unlock(&dentry->d_lock); spin_unlock(&inode->i_lock); if (!inode->i_nlink)