Re: Copyovering on SIG..., +mprotect

From: James Turner (turnerjh@XTN.NET)
Date: 05/02/98

Chris Jacobson <fear@ATHENET.NET> writes:

> I re-wrote parts of the stl.llist.h LList<> template, to use protected
> memory on the nodes.  It boiled down to protecting the nodes during add,
> prepend, append, insertafter, insertbefore, with an unprotection to any
> node requiring editing (at most, one node, and only in Append and the
> Insert functions), which would be re-protected.
> I used two macros:
> #define PROTECT(a) mprotect(a, sizeof(*a), PROT_READ)
> #define UNPROTECT(a) mprotect(a, sizeof(*a), PROT_READ | PROT_WRITE)

You definitely should check the results... these will fail if *a
doesn't use a multiple of pagesize bytes.  From the man page:

EINVAL  addr is not a valid pointer, or not a multiple of PAGESIZE.

So an mprotect on an improperly aligned buffer (ie not starting on a
multiple of PAGESIZE and being a multiple of PAGESIZE) will fail and
not change the protection of the memory.

James Turner     

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