Re: Security question: "Text file busy" overwriting executables but not shared libraries?

[Linus Torvalds]

In article <[e-mail]>,
Rob Landley  <[e-mail]> wrote:
>
>I.E. it seems like they go out of their way to ALLOW writing to the libaries. 
> (I assume they KNOW the difference between MAP_DENYWRITE, MAP_COPY, and 
>MAP_PRIVATE...?)

Note that the kernel will refuse to honour MAP_DENYWRITE from user
space, so I'm afraid that changing ld.so won't do a thing.

The reason the kernel refuses to honour it, is that MAP_DENYWRITE is an
excellent DoS-vehicle - you just mmap("/etc/passwd") with MAP_DENYWRITE,
and even root cannot write to it.. Vary nasty.

Which is why the kernel only allows it when the binary loader itself
sets the flag, because security-conscious application writers are
already aware of the "oh, a running binary may not be writable" issues.

So sorry..

		Linus