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X-HELO:	calimero.vinschen.de
Date:	Fri, 20 May 2016 21:58:39 +0200
From:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: Segfault in MAP_NORESERVE mmap above ~4GB
Message-ID:	<20160520195839.GF22065@calimero.vinschen.de>
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Hi Erik,

On May 12 15:30, Erik Bray wrote:
> Hi all,
>=20
> This issue pertains to Cygwin 64-bit.  The following example program
> demonstrates the issue:
>=20
> $ cat mmap_test.c
> #include <sys/mman.h>
> #include <stdio.h>
> #include <windows.h>
>=20
>=20
> #define VSIZE 0x100001000
> #define SIZE 0x1000
>=20
>=20
> void foo() {
>     void *top, *bot, *c;
>=20
>     c =3D mmap(NULL, VSIZE, PROT_READ|PROT_WRITE,
>              MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE, -1, 0);
>=20
>     top =3D c + VSIZE;
>     bot =3D top - SIZE;
>=20
>     printf("     c =3D 0x%016lx\n", c);
>     printf("   top =3D 0x%016lx\n", top);
>     printf("   bot =3D 0x%016lx\n", bot);
>=20
>     printf("  c[0] =3D %ul\n", *((unsigned long *)c));
>     printf("bot[0] =3D %ul\n", *((unsigned long *)bot));
> }
>=20
>=20
> int main(void) {
>     foo();
>     return 0;
> }
>=20
> $ gcc mmap_test.c -o mmap_test
>=20
> $ ./mmap_test.exe
>      c =3D 0x000006feffff0000
>    top =3D 0x000006ffffff1000
>    bot =3D 0x000006ffffff0000
>   c[0] =3D 0l
> Segmentation fault (core dumped)
>=20
> --------------------------------------------------

Thanks especially for the testcase.  I just applied a fix for this
which, hopefully, catches all problems with too small length/size
variables and parameters.

I've uploaded a new developer snapshot to https://cygwin.com/snapshots/

Would you mind to inspect the patch(*) critically?


Thanks a lot,
Corinna


(*) https://sourceware.org/git/gitweb.cgi?p=3Dnewlib-cygwin.git;a=3Dcommitd=
iff;h=3D0aa738220bb9dea2ad479e484560767b36701947

--=20
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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