What are some key tips for writing secure C code?

1. Validate Input: Always validate and sanitize input from external sources to prevent buffer overflows and other vulnerabilities. 2. Memory Management: Be cautious with dynamic memory allocation and deallocation to prevent memory leaks and vulnerabilities. Use functions like `malloc` and `free` responsibly. 3. Bounds Checking: Ensure that arrays and pointers are used safely by performing bounds checking to prevent buffer overflows. 4. Input Validation: Validate user input rigorously, checking for both type and range, to prevent injection attacks. 5. Avoid Global Variables: Minimize the use of global variables to reduce the risk of unintended side effects and improve code maintainability.

To write secure C code, prioritize input validation to prevent buffer overflows and attacks. Opt for safer functions like strncpy over strcpy. Handle pointers carefully to avoid memory leaks and null dereferences. Always initialize variables and diligently check function return values. Minimize the use of global variables for better security. Utilize both static and dynamic analysis tools for detecting vulnerabilities. Practice secure memory management, especially with functions like free to avert memory corruption. Keep updated with security patches for the C standard library. Aim for clear, straightforward code, reducing the likelihood of security issues. Stay aware of common security pitfalls in C to ensure robust, safer applications.

Most have been said already in the title: "Use secure libraries", but it should be emphasize that there are a few ways to check the viability of a library. - if it is included in the C standard library, it means it passed the test for the community and is, then, considered safe. - if it's an open source library, then the code should be easily scannable for vulnerabilities - else you'll have to check through different communities or user's feedbacks. NB: Any safe library today is still susceptible, even though very unlikely, to be found unsafe in the future.

Increase the security of your C code by utilising trustworthy and validated secure libraries. These expert-approved libraries include dependable functions for tasks like as input validation, encryption, hashing, random number generation, and memory management. Using such libraries ensures safer and more efficient implementation of common operations, lowering the risk of code vulnerabilities.

When we talk about secure C code, I presume that we're talking about the secure memory management. C is really terrible in terms of safety and has a lot of memory leaks and lot of vulnerabilities. Since it has direct access to the Computer's memory we can have a risk of altering the memory. Always use a GCC extensions to your code so that it cleans up the variable whenever the attribute goes out of scope by attaching a destructor function to a variable. As a new age programmer I suggest everyone to learn RustC instead of just C because of the best memory safety it offers. Many of the kernels are rewritten in RustC just for it's memory safety.

As C is a language often use in quite specific cases, not much for mobile development, or website building (which are softwares where user are accustomed to eventual bugs or crash), it is important to keep it as strict as possible. Some examples of modern day C usage are - embedded software, which sometimes isn't possible to update from distance - native development for mobile (Google NDK) - I/O server side for creating internal logs or different files. So when writing a function, always thinking about it being a independent block that should handle errors on its own, might takes a bit of effort but in the usage of C, it is very welcome.

Using unsafe functions can achieve the outcome but then put the code at risk. The way to avoid Safe code is to program using Visual Studio and this gives warnings when Unsafe code is used.

Memory management and validating inputs and outputs go hand in hand with C programming. Whenever you are managing a pointer ensure you initialize it to NULL, check for NULL before performing any operations and ensure you reset it to NULL after freeing any associated memory or when it is no longer pointing to a valid area of memory. When indexing arrays or using pointer arithmetic ensure that you will not go out of bounds of the valid memory area.

Always try to wipe the memory from the data that you will not use in the future (Cashe). Also always you must check for null values

In C, memory management is an art. As mentioned, in the article, tools will be your best friends. I've personally used Valgrind for a while, and it has always been very helpful. From a debugging perspective, making smaller independent chunks of code, could be of great help in checking which part of the code is leaking memory, as C doesn't provide any garbage collector by default. Some library provides garbage collectors, such as the Boehm–Demers–Weiser garbage collector but will make the program much heavier, so it will depends on the requirements of the project: if program size is important, then valgrind check might be the best option, even though time consuming, but if the size isn't an issue, a GC library might be your best bet.

follow some coding standards and guidelines that can help you improve the quality, readability, and maintainability of your code Do not depend only on automation tools Check the logic and the flow of your code

While writing a code in C, you can implement SAST solution which will support you if there are any security gap in your code.