Medline Plus (from the U.S. National Library of Medicine and the National Institutes of Health) has this on its page about canker sores:

The easiest home remedy is to apply hydrogen peroxide (1 part hydrogen peroxide and one part water with a cotton swab) to the canker sore. Then dab a small amount of milk of magnesia on the canker 3-4 times a day. This is not only soothing, but appears to help healing. (This won't get rid of the underlying virus that causes canker sores, though.)

It also says that gargling with a mild salt-water rinse "may help" -- but doesn't say ANYthing about scrubbing with salt. That sounds extremely painful. There is that old expression about rubbing salt in a wound ....

I'm sure the Medline site is talking about the hydrogen peroxide you get on the grocery store shelf (and note that even it is diluted in this case), not the high-test stuff Gary is talking about. Stay away from that!

And note this, also from Medline:

Oral cancer is not a complication of canker sores -- so stop panicking every time you find one in your mouth! If it lasts more than two or three weeks without starting to heal, though, get it checked out.

In any case, Carl -- quit smoking and scrubbing!

All the best,

Leslie