find searching in parent directories instead of subdirectories

git rev-parse --show-toplevel

will print out the top level directory of the current repository, if you are in one.

Other related options:

# `pwd` is inside a git-controlled repository
git rev-parse --is-inside-work-tree
# `pwd` is inside the .git directory
git rev-parse --is-inside-git-dir

# path to the .git directory (may be relative or absolute)
git rev-parse --git-dir

# inverses of each other:
# `pwd` relative to root of repository
git rev-parse --show-prefix
# root of repository relative to `pwd`
git rev-parse --show-cdup

A generalized version of Gilles' answer, first parameter used to find match:

find-up () {
  path=$(pwd)
  while [[ "$path" != "" && ! -e "$path/$1" ]]; do
    path=${path%/*}
  done
  echo "$path"
}

Keeps the use of sym-links.

An even more general version that allows using find options:

#!/bin/bash
set -e
path="$1"
shift 1
while [[ $path != / ]];
do
    find "$path" -maxdepth 1 -mindepth 1 "$@"
    # Note: if you want to ignore symlinks, use "$(realpath -s "$path"/..)"
    path="$(readlink -f "$path"/..)"
done

For example (assuming the script is saved as find_up.sh)

find_up.sh some_dir -iname "foo*bar" -execdir pwd \;

...will print the names of all of some_dir's ancestors (including itself) up to / in which a file with the pattern is found.

When using readlink -f the above script will follow symlinks on the way up, as noted in the comments. You can use realpath -s instead, if you want to follow paths up by name ("/foo/bar" will go up to "foo" even if "bar" is a symlink) - however that requires installing realpath which isn't installed by default on most platforms.