Messages in this thread | | | Date | Fri, 02 Nov 2001 18:39:53 -0500 | From | Brian Gerst <> | Subject | Re: null pointer questions |
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Brian Gerst wrote: > > Ken Ashcraft wrote: > > > > > > 2. What happens if I pass a null pointer as the destination parameter > > > > to copy_from_user? Does copy_from_user handle it safely or will the > > > > kernel seg fault? > > > > > > The kernel won't crash, but it might fail (depending on whether 0 is a > > > valid user space address or not). > > > > Why does it matter if 0 is a valid user space or not? If I make the call > > > > copy_from_user(0, user_ptr, 4); > > > > the null pointer is the kernel address, not the user address. Can you > > clarify please? > > copy_from_user uses the string move instruction on the x86, so the > exception code would assume the source faulted not the dest. It would > return -EFAULT instead of causing an oops.
Err, would return non-zero instead of -EFAULT.
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