wsl1 exec format error fix

wsl1 exec format error fix

Given that Microsoft has effectively deprioritized addressing core issues in WSL1, I’ve implemented a workaround for this issue with ELF binaries.

The solution uses a custom wrapper (elf_wrapper.c) with ld.so.preload to automatically intercept and redirect ELF execution through /lib64/ld-linux-x86-64.so.2, enabling system-wide compatibility without user intervention. Unlike direct invocations of /lib64/ld-linux-x86-64.so.2, this approach captures ELF execution at the system level, eliminating the need for wrapper scripts, shell aliases, or direct binary modifications with patchelf.

elf_wrapper.c source code:

#define _GNU_SOURCE
#include <dlfcn.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>

// Path to the ELF interpreter used to execute ELF binaries
static const char *ld_linux_so = "/lib64/ld-linux-x86-64.so.2";

// Pointer to the original execve function
static int (*original_execve)(const char *filename, char *const argv[], char *const envp[]) = NULL;

// Wrapper function for execve
int execve(const char *filename, char *const argv[], char *const envp[]) {
    if (!original_execve) {
        // Load the original execve function
        original_execve = dlsym(RTLD_NEXT, "execve");
    }

    // Check if the original file has the SUID bit set
    struct stat file_stat;
    if (stat(filename, &file_stat) == 0 && (file_stat.st_mode & S_ISUID)) {
        // If the SUID bit is set, call the original execve directly
        return original_execve(filename, argv, envp);
    }

    // Check if the file is an ELF binary
    FILE *file = fopen(filename, "rb");
    if (file) {
        char magic[4];
        fread(magic, 1, 4, file);
        fclose(file);

        // Check the ELF magic number: 0x7f 0x45 0x4c 0x46
        if (memcmp(magic, "\x7f""ELF", 4) == 0) {
            int argc;
            for (argc = 0; argv[argc] != NULL; argc++);

            char **new_argv = malloc((argc + 2) * sizeof(char *));
            new_argv[0] = (char *)ld_linux_so;
            new_argv[1] = (char *)filename;

            int i;
            for (i = 1; i < argc; i++) {
                if (argv[i] != NULL) {
                    new_argv[i + 1] = argv[i];
                }
            }

            new_argv[i + 1] = NULL;  // Finalize the array with NULL

            // Execute the binary with the ELF interpreter
            int result = original_execve(ld_linux_so, new_argv, envp);
            free(new_argv);
            return result;
        }
    }

    // If not ELF, execute normally
    return original_execve(filename, argv, envp);
}

Run:

sudo gcc -shared -fPIC -o /usr/local/lib/libelf_wrapper.so elf_wrapper.c -ldl
echo "/usr/local/lib/libelf_wrapper.so" | sudo tee -a /etc/ld.so.preload