Smallest Palindrome from a String

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

char *strrev ( char *str ) {
    int i, len=strlen(str);
    char *rev = malloc(len+1);
    rev[len] = '\0';
    for (i=len-1; i>=0; rev[i--]=*str++);
    return rev;
}

int main(int argc, char *argv[]) {
    if (argc!=2)
        puts("Usage: small_palin <string>");
    else {
        char *str = argv[1];
        int i=0, j, len=strlen(str);
        while ( strcmp(str+i,strrev(str+i))!=0 )
            ++i;
        char *palin = malloc(len+1+i);
        *(palin+len+1+i) = '\0';
        strcpy(palin,str);
        str[i]='\0';
        strcpy(palin+len,strrev(str));
        puts(palin);
    }
    return 0;
}