How to analyze syscalls in Linux

Introduction:

System call logging in Linux is a powerful method for understanding program behavior and detecting errors or security vulnerabilities.

Example:

Let's say we want to analyze a program called "first-script.sh", which simply displays the message "Welcome to shell Scripting!" on the screen.

Enable syscall logging: To enable syscall logging for this program, we can use the "strace" utility as follows:

This will launch the "first-script.sh" program and save the results of the syscall logging to a file called "trace.txt".

Analyze the results: After running the program, we can open the "trace.txt" file to see the results of the syscall logging. Here is an excerpt from the file for our example:

These lines show the syscalls made by the "first-script.sh" program during its execution. For example, the first line shows the "execve" system call to run the "first-script.sh" program. The second line shows the "brk" system call to allocate memory. The other lines show system calls to access open files.

Interpret the results: By interpreting the results of the syscall logging, we can understand the behavior of the program and detect security vulnerabilities or errors. In our example, we can see that the program only performs a few simple system calls and does not have any security or memory leakage issues.

here are some commonly used options for the strace command in Linux along with examples:

• -p <pid>: Attach to an existing process with the given process ID and trace its system calls. For example, strace -p 1234 will attach to the process with PID 1234 and trace its system calls.
• -o <file>: Write the output to the specified file instead of standard output. For example, strace -o output.txt ./myprogram will run myprogram and write the output of strace to output.txt
• -e <syscall>: Specify a comma-separated list of system calls to trace. For example, strace -e open,read ./myprogram will only trace the open and read system calls made by myprogram.
• -c: Print a summary of the system calls traced, including how many times each call was made and how much time was spent in each call. For example, strace -c ./myprogram will run myprogram and print a summary of the system calls traced.

Conclusion :

In summary, syscall analysis is a powerful tool for understanding program behavior in Linux. By using utilities such as "strace" or "ltrace", we can capture the system calls made by a program, analyze them, and interpret them to improve the quality and security of software.