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From: "yangyanchao6 at huawei dot com" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug dynamic-link/20019] NULL pointer dereference in libc.so.6 IFUNC
 due to uninitialized GOT
Date: Thu, 11 Mar 2021 06:24:21 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D20019

--- Comment #28 from yangyanchao6 at huawei dot com <yangyanchao6 at huawei=
 dot com> ---
(In reply to H.J. Lu from comment #27)
> (In reply to yangyanchao6@huawei.com from comment #26)
> > (In reply to H.J. Lu from comment #24)
> > > Fixed for 2.33 by
> > >=20
> > > commit 6ea5b57afa5cdc9ce367d2b69a2cebfb273e4617
> > > Author: H.J. Lu <hjl.tools@gmail.com>
> > > Date:   Mon Dec 28 05:28:49 2020 -0800
> > >=20
> > >     x86: Check IFUNC definition in unrelocated executable [BZ #20019]
> >=20
> > I tried this patch but the problem didn't get fixed.
> > Is there anything else I need to do?
>=20
> What problem did you run into?

[root@localhost DTS2021030805K7VLP1D00]# cat bar.c=20
void
bar (void *dst, void *src)
{
  __builtin_memmove (dst, src, 40);
}
[root@localhost DTS2021030805K7VLP1D00]# cat foo.c=20
void bar (void *dst, void *src);

void
foo (void)
{
  char dst[50];
  char src[50];
  bar (dst, src);
}
[root@localhost DTS2021030805K7VLP1D00]# cat main.c=20
void foo (void);

int
main ()
{
  foo ();
  return 0;
}
[root@localhost DTS2021030805K7VLP1D00]# gcc -O2   -c -o main.o main.c
[root@localhost DTS2021030805K7VLP1D00]# gcc -O2 -fPIC   -c -o foo.o foo.c
[root@localhost DTS2021030805K7VLP1D00]# gcc -O2 -fPIC   -c -o bar.o bar.c
[root@localhost DTS2021030805K7VLP1D00]# ld.gold -shared  -z now -o libbar.=
so
bar.o
[root@localhost DTS2021030805K7VLP1D00]# ld.gold -shared  -z now -o libfoo.=
so
foo.o libbar.so
[root@localhost DTS2021030805K7VLP1D00]# gcc -o foo main.o libfoo.so
-Wl,-rpath,.=20
[root@localhost DTS2021030805K7VLP1D00]# ./foo=20
./foo: Relink `./libbar.so' with `/usr/lib64/libc.so.6' for IFUNC symbol
`memmove'
Segmentation fault (core dumped)
[root@localhost DTS2021030805K7VLP1D00]# readelf -r libbar.so

Relocation section '.rela.plt' at offset 0x2b0 contains 1 entry:
  Offset          Info           Type           Sym. Value    Sym. Name +
Addend
000000001ff8  000100000007 R_X86_64_JUMP_SLO 0000000000000000 memmove + 0

It looks the same as it did before the patch was incorporated.

--=20
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