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Asked: 2026-06-15T13:41:17+00:00

I feel like this question has been answered but no implementation I’ve found from

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I feel like this question has been answered but no implementation I’ve found from googling it has offered the protection I need.

I am working with linux 3.2.2.

I wish to copy variables from user space to kernal space as safely as possible. This includes a struct pointer, and a null terminated string. How could i ensure my struct pointer is valid? (access_ok on (void*) -1 does not catch it) I want it to be basically idiot proof…

For the null terminated string i don’t know the length and some of the functions that copy these null terminated strings want a size.

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1 Answer

  1. Editorial Team

    Solved: So the best solution I found was actually the code I was using just put an and instead of an or.

    check if ptr is null first of all.
    then

    access_ok(VERIFY_READ/WRITE,ptr,structsize)

    if this passes our usr ptr or struct is within the user address space.
    finally use 

    int copy_from_user(void* dest, void* src,size_t len)

    and make sure destPtr points to a space in kernel thats size is obviously >= structsize.
    Even now there is no guarantee that the data in the structure is useful, or what you want at all. It just is raw data that will not cause a kernel panic. So now you can check each member of the struct for valid data. there is some more useful information on this

    https://www.ibm.com/developerworks/linux/library/l-kernel-memory-access/

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