BUG? Missing dput() in ovl_permissions().

I apologize for not having tested this on the latest kernel. I hit this bug in SUSE SLES12 and by inspection it still appears to be in Linus's kernel.

Failure to free dentry. Missing dput() using default_permissions in ovl_permission().

# mount overlayfs with default_permissions
mkdir l u m
mount -t tmpfs tmpfs u
mount -t overlayfs -o upperdir=u,lowerdir=l,default_permissions overlayfs m
dd if=/dev/zero of=m/test_dput bs=4096b count=1000
df u l m
rm m/test_dput
df u l m
# tmpfs space is not freed!

umount m u
# BUG. Dentry still in use!

It appears that there may be a missing dput() in the ovl_is_default_permissions(inode) path of ovl_permission().

I hit this in SUSE because default_permissions was getting set by accident due to uninitialized data in ovl_config (kalloc vs. kzalloc). This bug is fixed upstream.

-Eric Jones