17. $f(x)$ is a function defined on $\mathbf{R}$ that is odd, and satisfies the following conditions: (1) For any $x, y \in \mathbf{R}$, $f(x+y)=f(x)+f(y)$; (2) When $x>0$, $f(x)<0$, and $f(1)=-2$. Find the maximum and minimum values of $f(x)$ on the interval $[-2,3]$.