What diet is for kidney problems?

Depends on problem. Diet restriction depends on the problem. Chronic kidney disease- usually sodium, potassium, and some protein restriction; possibly phosphorus restriction. Stone disease usually increased water intake. Always check with your doctor and may be nephrologist before making any changes in the diet.
Low salt & protein. Low salt is healthy for all and especially for calcium kidney stone formers. Modest protein intake, i.e. Avoid those 32oz steaks, avoids "overworking" kidney.