C Puzzles

Given a string s1 and a string s2, write a snippet to say whether s2 is a
rotation of s1 using only one call to strstr routine?

(eg given s1 = ABCD and s2 = CDAB, return true,
given s1 = ABCD, and s2 = ACBD , return false)


I hope this will work:
strcpy (s3,s1); //s3 = ABCD
strcat (s1,s3); // s1 = ABCDABCD
then check for strstr(s1,s2);