There's a few areas to cover:
Sphinx Searching
- does not use SQL, and cannot modify data, so this is safe.
Underlying searches for ActiveRecord objects, using search results
from Sphinx
- Uses hash arguments in #find calls - which ActiveRecord sanitises,
I'm pretty certain
- Can pass arguments to :order option if using :sql_order in your
search calls. Does AR sanitise :order?
Sphinx Indexing
- Uses SQL statements
- Only defined within a define_index block - so you'd have to have
some Ruby injection happening to have any effect on that (to change
the sql contents and then regenerate the config file and re-index
Sphinx).
--
Pat