Question 1

How to use LD_PRELOAD to mock system time for testing?

Accepted Answer

Use libraries like libfaketime or timeskew from the Awesome LD_PRELOAD list. Set the LD_PRELOAD environment variable to the library path and configure it to return specific times, allowing you to test time-dependent code without source changes.

Question 2

What are the best LD_PRELOAD tools for debugging filesystem access?

Accepted Answer

Tools like fsatrace for tracing filesystem operations and cleancache for managing page cache are listed. These help monitor or modify file access patterns in applications, useful for debugging backup or logging software.

Question 3

LD_PRELOAD vs Frida for dynamic instrumentation – which is better?

Accepted Answer

LD_PRELOAD is Linux-specific and lower-level, ideal for simple library function overriding. Frida is cross-platform and more flexible for complex hooking. For basic interception on Linux, LD_PRELOAD is lightweight; for advanced cross-platform needs, Frida might be preferred.

Question 4

How to create a custom LD_PRELOAD library to override functions like malloc?

Accepted Answer

Write a shared library in C with functions matching the target signatures, compile with -shared -fPIC flags, and set LD_PRELOAD to its path. Refer to examples in the Awesome LD_PRELOAD list, such as unrandom for srand overrides, for guidance.

Question 5

Are there security risks with using LD_PRELOAD?

Accepted Answer

Yes, LD_PRELOAD can be exploited for privilege escalation or malware injection, as it allows arbitrary code execution. Always verify library sources and use in trusted environments; some systems disable it for security hardening.

Question 6

Can LD_PRELOAD add TLS support to legacy applications?

Accepted Answer

Yes, tools like ktlswrapper in the list intercept network calls to enable TLS encryption without modifying source code. This is useful for securing older applications that lack built-in TLS support.

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