I had a Pit/GSD mix who was extremely friendly. From the time I got her as a 7lb puppy, I started training her not to jump on people, but to sit and wait to be pet. She would go up to everyone at the dog park, and sit politely, waiting to be pet, before she would run and play with the other dogs. She had excellent recall, and could lie-down-stay forever, even if I was standing 100 feet away, and dangling her favorite toy. She also could heel off-leash.
But I think if someone attacked me, she would attack them.
I base this on two things. One is that the first time she saw me signing with Deaf-blind person-- that is, hand-over-hand, she got confused, and started barking in a threatening way. I had to put her on a lie-down-stay. She continued to growl a little until she got used to this person being around, and the way we communicated.
The second was the time I took her to the vet with a couple of the cats. Normally, I did not take dogs and cats to the vet together, but this time, she was in the waiting room with two cats in a carrier. Usually, in the waiting room, she would play with whatever other friendly dog was there: they’d play-wrestle, and chase a little. Not that day. That day, she sort of wrapped herself around the cat carrier, and growled at any dog who ventured near. It was totally unexpected (on my part).
So she had a very strong protective streak.
FWIW, though, this was the sweetest, most affectionate dog in the world with me: she slept with me, and liked to be spooned. When my husband came into the picture, she loved having another person to pet her. She didn’t mind sharing the bed with him, but sometimes she’d try to sleep between us.
If people were friendly to me, she was very friendly to them.
She really was just the best dog ever.
She’s been gone for 12 years, and it still hurts.