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Date: Tue, 09 Oct 2007 18:56:19 +0200
From: Paolo Bonzini <paolo.bonzini@lu.unisi.ch>
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Subject: Re: [Bug 9138] New: kernel overwrites MAP_PRIVATE mmap
References: <bug-9138-27@http.bugzilla.kernel.org/> <20071009083913.212fb3e3.akpm@linux-foundation.org> <470BA58F.8050907@lu.unisi.ch>
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This testcase is not a regression, but it is still a bug, and I believe
the root cause is the same: in this case, it is ftruncate modifying the
length of MAP_PRIVATE mmaps.


#include <sys/mman.h>
#include <fcntl.h>
#include <stdio.h>

int main()
{
   system ("echo foo > gst.im");
   int f = open ("gst.im", O_RDONLY);

   char *p = mmap(NULL, 1628636, PROT_READ, MAP_PRIVATE, f, 0);
   close (f);
   f = open("gst.im", O_RDWR|O_CREAT, 0666);
   printf ("%s", p);
   ftruncate (f, 0);
   mmap(NULL, 401408, PROT_READ|PROT_WRITE|PROT_EXEC,
        MAP_PRIVATE|MAP_ANON, -1, 0);
   printf ("%s", p);
}


Expected (and this is what it gives on e.g. Darwin):

foo
foo

Actual output:

foo
Bus error


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