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You should have the program loader (the bootloader in the case of Note how the secret guard value is hard-coded rather than being decided during Noreturn void _stack_chk_fail ( void ) void foo ( const char * str ) Robustly because the compiler did it itself. Optimize these checks away if you wrote them yourself, this only works The вЂњstack smashedвЂќ message in the standard error stream is not even present on all platforms, and it can take lots and lots of time to figure out what happened, especially if you are running a third-party native library with no source code./* Note how buffer overruns are undefined behavior and the compilers tend to I hope the post saves someone an all-nighter or two when facing abrupt JVM death without even a crash log. Why the abortion is done without a more detailed error log is a different question and outside the scope of this post. So the JVM adds guard values to the memory, and if these values are mangled after the native method finishes, terminates the application immediately. Going back to the allegedly safe JavaВ world, such a buffer overflow may corrupt internal JVM structures, or even enable whoever it was that supplied the string to execute arbitrary code. While in this example using snprintf and enabling sanitization will definitely help, the error may easily be much more subtle than that and not caught automatically.

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In some cases the code might complete seemingly fine, but in some cases you can encounter buffer overflows.

The results of running such code can become completely unpredictable. When the code is compiled without the sanitization in place, as in the following example, gcc -fno-stack-protector CheckSumCalculator.c -o CheckSumCalculator.so Having compiled the code with the stack protector in place, the implementations of either the runtime library or the OS may detect this situation in some conditions and terminate the program to prevent unexpected behavior. The available safety nets will vary significantly from compiler to compiler, and even between different versions of the same compiler, but hereвЂ™s an example: gcc -fstack-protector CheckSumCalculator.c -o CheckSumCalculator.so Other than using the much safer snprintf that takes buffer length and does not write past that, you can also ask the compiler to add stack protectors, or memory sanitization to the compiled code. This will indeed result in stack smashing and opens doors for potential hacks or just leaving the application to an unpredictable state.ДЇor C-developers, the underlying stack protector mechanism is well-known, but for Java developers, it might need a bit more explanation. With longer inputs the remaining characters will be written past its end. Sprintf(dst_filename, '%s.digested', src_filename) ДЇrom the above it is clear that the buffer can only hold a fixed number characters. The underlying problem is not too complex and is probably immediately visible in the C code: char dst_filename

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You should be aware of the fact that I only tested the examples on Linux and Mac OS X, and it might behave differentlyВ onВ Windows. Instead, the JVM is crashed without so much as a crash log.

So the native method finished its execution just fine, but the control was not returned to Java. *** stack smashing detected ***: java terminated The not-so straightforward part is exposed when you discover yourself staring at the output with a slightly different (longer) filename used for input: $ java -jar build/libs/checksum.jar 123456789012.txt

Got checksum from native method: 1804289383 $ java -jar build/libs/checksum.jar 123.txtД®xiting native method with checksum: 1804289383 You would just need to clone the repository and launch it similar to the following example: $. The code is simple and straightforward and so is running it. To achieve Awesome Performance (TM), I decided to implement the checksum calculation partВ using native implementation. It consists of a simple Java class, calculating checksums for files. To walk you through the experience, I have created a small test case. Or in more detail, how using native methods can result in JVM crashing silently without any reasonable traces in log files. This post is about a recent experience with native methods. I am also sure that the surprise has later vanished over the years with coming to understand how the JVM handles calls to native implementations via JNI. I bet every Java developer has been surprised at some point in the beginning of their career when they first encounter native methods in Java code.

Stack smashing detected