Linux EFAULT (errno 14) — Bad Address (Memory Access Error)

Overview

Linux EFAULT error occurs when a system call is given a pointer to invalid memory, indicating a programming bug or memory corruption in the application.

Key Details

• EFAULT (errno 14) means a system call was passed a pointer outside the process's accessible address space
• This is almost always a programming bug — passing NULL, freed, or uninitialized pointers to syscalls
• The kernel validates user-space pointers before accessing them and returns EFAULT if invalid
• Unlike SIGSEGV which crashes the process, EFAULT is returned as an error code allowing recovery
• Common in C programs with incorrect memory management

Common Causes

• Passing NULL pointer to a system call that expects valid memory
• Using a pointer to freed memory (use-after-free)
• Buffer allocated on the stack that has gone out of scope
• Incorrect pointer arithmetic pointing outside allocated buffer
• Memory corruption from buffer overflow in a different part of the program

Steps

1. 1Run the program under Valgrind: valgrind --track-origins=yes ./program to detect memory errors
2. 2Compile with AddressSanitizer: gcc -fsanitize=address -g program.c
3. 3Use strace to identify which system call returns EFAULT: strace -e trace=all ./program
4. 4Enable core dumps: ulimit -c unlimited, then analyze with gdb ./program core
5. 5Review code for NULL pointer checks before system calls

Tags

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Frequently Asked Questions