Computers and Technology, 12.02.2020 03:25 steph2478
The PATH environment variable.
The system (const char *cmd) library function can be used to execute a command within a program. The way system (cmd) works is to invoke the /bin/sh program, and then let the shell program to execute cmd. Because of the shell program invoked, calling system() within a
Set-UID program is extremely dangerous. This is because the actual behavior of the shell program can be affected by environment variables, such as PATH. These environment variables are under user’s control. By changing these variables, malicious users can control the behavior of the Set-UID program. In bash, you can change the PATH environment variable in the following way (this example adds the directory /home/sec-lab to the beginning of the PATH environment variable):
sudo su
export PATH=/home/sec-lab:$PATH
The Set-UID program below is supposed to execute the /bin/ls command; however, the programmer only uses the relative path for the ls command, rather than the absolute path:
Create a file: make sure you are still in the bin folder (if not cd /bin)
nano setUID. c
copy the code to the file
#include
int main()
{
system("ls -la");
return 0;
}
gcc –o setUID setUID. c //this is to compile the c code
./setUID //to execute the executable file
Notice the output of files
cd /usr/local/
ls –la
Notice the bin folder is root (normal users, process and program should not have direct access) and your program had access to as it used the setUID
Question 12 - Can you let this Set-UID program (owned by root) run your code instead of /bin/ls? If you can, is your code running with the root privilege? Describe and explain your observations.
Answers: 3
Computers and Technology, 21.06.2019 23:00
Explain briefly why you cannot expect to find a previous version of every file with which you work.
Answers: 1
Computers and Technology, 22.06.2019 20:00
What is the worst-case complexity of the maxrepeats function? assume that the longest string in the names array is at most 25 characters wide (i.e., string comparison can be treated as o( class namecounter { private: int* counts; int nc; string* names; int nn; public: namecounter (int ncounts, int nnames); int maxrepeats() const; }; int namecounter: : maxrepeats () { int maxcount = 0; for (int i = 0; i < nc; ++i) { int count = 1; for (int j = i+1; j < nc; ++j) { if (names[i] == names[j]) ++count; } maxcount = max(count, maxcount); } return maxcount; }
Answers: 3
Computers and Technology, 22.06.2019 21:00
Kirk found a local community college with a two-year program and he is comparing the cost with that of an out-of-state two-year school. what is the expected total cost for one year at the local community college if kirk lives at home? what is the expected total cost for one year at the out-of-state school if kirk lives on campus?
Answers: 2
Computers and Technology, 23.06.2019 09:30
Write an essay on online collaboration, how to do it, the challenges, resolving the challenges, and consider whether the risks are greater than rewards. ( need )
Answers: 1
The PATH environment variable.
The system (const char *cmd) library function can be used...
The system (const char *cmd) library function can be used...
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