How to get userID when writing Linux kernel module

Question

Here is my function in my kernel module which I insert using insmod command after make at later stages. I am working on goldfish (2.6.29)

Answer 1

Getting the UID without using the getuid syscall hook:

#include "linux/cred.h"

static inline uid_t get_uid(void) {
#if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 5, 0)
#include "linux/uidgid.h"
    // current_uid() returns struct in newer kernels
    return __kuid_val(current_uid());
#else
    return 0 == current_uid();
#endif
}

You should also look through linux/uidgid.h for useful macros that define ROOT uid/gid as well as inline comparison functions to avoid directly calling __kuid_val().

For example, a common use would be to check if the user is root:

static inline bool is_root_uid(void) {
#if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 5, 0)
#include "linux/uidgid.h"
    // current_uid() returns struct in newer kernels
    return uid_eq(current_uid(), GLOBAL_ROOT_UID);
#else
    return 0 == current_uid();
#endif
}