wierd current->uid in module

[project8sem4@fastmail.fm]

hi
 i am doing a project on
 a very simple system call interception module.
 the module is supposed to return the  uid of the 
user who made the call to the syscall. i m trying to 
do it thus:
 
//in the kernel module
 asmlinkage long my_syscall(arg1,arg2)
 {
         sprintf(buffer, "%s%s%i", arg1,arg2,current->uid);
         //this buffer is later read.
         return original_syscall(arg1,arg2);
 }
 
the problem is that the uid returned is always -1 
whether the user is root or otherwise. 
could you suggest a way out please.
 thanx
 -kt
 

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