Write a function good_echo that reads a line from standard input and writes it to standard output. Your implementation should work for an input line of arbitrary length. You may use the library function fgets, but you must make sure your function works correctly even when the input line requires more space than you have allocated for your buffer. (Hint, think about read only to the limit of your buffer, print out the content of the buffer to standard output and then reuse the buffer to read more from the standard input.) You code should also check for error conditions and return when one is encountered.
You should create a directory called ’hw5’ for this assignment. And in the directory ’hw5’ you should have two files: ’good_echo.c’ and ’Makefile’. You submit hw5.tar file to Canvas. good_echo.c should contain the definition of ’good_echo()’ function and also ’main()’ function that invokes ’good_echo()’. In other words, good_echo.c should be a program that can be compiled to an executable that can run and read in one line (only one line) of standard input and echo to the output and then terminate. Makefile should contain proper makefile rules so that when you enter ’make’ in your terminal, you will produce the following files: 1. good_echo.s (the assembly code for your c program), 2. good_echo.o (the relocatable object file produced from your c program), 3. good_echo (the executable program from your c program). And you must also compile your code so that you turn on the canary value stack protection. You can check if you have successfully inserted canary stack protection by looking at the .s file. In particular to look for the line that says ’call__stack_chk_fail’. Your Makefile should also contain the following line at the end of the file so that you can use command ’make clean’ to remove all the byproducts of your program.
.PHONY: clean clean: rm -f good_echo.o good_echo.s good_echo
Paper For Above instruction
The task involves developing a robust C program that reads a line of arbitrary length from standard input and echoes it to standard output, ensuring the program handles input lines longer than its buffer size without errors. The implementation emphasizes trailing the use of fgets for buffered reading, but with the precaution to process the input in chunks if necessary. Additionally, the program must incorporate security features like stack canary protection to prevent buffer overflow attacks, and a Makefile must be created to compile the code with such protections enabled, generating assembly, object, and executable files as specified.
Implementing a function called good_echo requires attention to dynamic input handling, ensuring the
process works for varying input lengths. The primary challenge involves reading input in segments that do not exceed the buffer size, printing each segment, and repeating until the entire line has been processed. This approach involves careful buffer management, reading input up to the buffer limit, printing, and then reading further, with appropriate checks for errors such as read failure or end-of-file conditions.
The program structure should include a main() function that calls good_echo(), facilitating a straightforward compilation to an executable, which can be run from the command line for testing. The program should terminate after processing one full line of input, aligning with the requirement to echo only a single line per execution. Error checking is vital—if any system call such as read or fgets fails, the program should gracefully exit, reporting or handling errors as appropriate.
From a security standpoint, enabling stack canary protection involves compiling with the flag -fstack-protector-strong or similar options, which is specified in the Makefile. After compilation, the presence of the call to __stack_chk_fail in the assembly confirms that stack protection is active. This security feature adds a safeguard against buffer overflow exploits by inserting a canary value before the return address in the stack frame, which is checked upon function return.
Creating a proper Makefile requires defining rules to compile the C code into assembly (.s), object (.o), and final executable. Also, including a clean rule allows for easy cleanup of intermediate files. The Makefile should account for the necessary compile flags that enforce stack protection along with standard compilation options, thereby ensuring the executable is both correct and secure. Testing the output assembly file verifies that protections are correctly inserted, ensuring robustness and security of the implementation.
References
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GNU Make Manual. (2022). Makefile syntax and rules. Free Software Foundation. Retrieved from https://www.gnu.org/software/make/manual/make.html