程序代做CS代考 #include

#include
#include

/**

1) as root, compile race.c (use the makefile), make race
cd /questions/race
make

2) Verify that hacker can not view or edit /etc/passwd2

3) Explain what the setuid bit being set means for race, when run by hacker.

4) As hacker, run /questions/race/race to understand how it works and what it does

5) As hacker, explain how hacker exploits /questions/race/race
so that they modify the root only readable and writable file /etc/passwd2

6) As hacker, explain how hacker exploits /questions/race/race
so that they end up with a root shell

Be careful when doing this you may lock yourself out of the system!!
I have made a backup of /etc/passwd in /etc/passwd.bak
make sure you have a root shell when playing with the passwd
file.

7) Fix the code below so that it eliminates the race condition and
allows race to safely write to /tmp/permitted, no matter which user
owns the file.

References:
http://www.cis.syr.edu/~wedu/seed/Labs_12.04/Software/Race_Condition/Race_Condition.pdf
http://www.csl.mtu.edu/cs3451/www/notes/ch6%20-%20Adding%20new%20users.pdf

**/

int main(int argc, char ** argv) {
char * fn = “/tmp/permitted”;
char buffer[128];
FILE *fp;

if(!access(fn, W_OK)){
scanf(“%100s”, buffer );
fp = fopen(fn, “w”);
fwrite(“\n”, sizeof(char), 1, fp);
fwrite(buffer, sizeof(char), strlen(buffer), fp);
fclose(fp);
} else {
printf(“No permission \n”);
}
}