From: Xi Ruoyao <xry111@mengyan1223.wang>
To: Reinoud Koornstra <reinoudkoornstra@gmail.com>
Cc: Florian Weimer <fweimer@redhat.com>,
Reinoud Koornstra via Gcc-help <gcc-help@gcc.gnu.org>
Subject: Re: Fortify_source and stack-protector-strong
Date: Thu, 03 Mar 2022 04:23:40 +0800 [thread overview]
Message-ID: <204cd10c9d34c6c798e701f1d990c120c2d77897.camel@mengyan1223.wang> (raw)
In-Reply-To: <CAAA5faE_s_4LWSDcTJxhdNUdD5_ELgWx=pVmJorf57Koesp_xg@mail.gmail.com>
On Wed, 2022-03-02 at 12:05 -0800, Reinoud Koornstra wrote:
> Hi Xi,
>
> Thanks for your reply.
> Then what is the difference between -D_FORTIFY_SOURCE=1 and -D_FORTIFY_SOURCE=2 exactly?
-D_FORTIFY_SOURCE=1 uses __builtin_object_size(..., 0) as the buffer
size, but -D_FORTIFY_SOURCE=2 uses __builtin_object_size(..., 1). Read
https://gcc.gnu.org/onlinedocs/gcc/Object-Size-Checking.html for the
details.
One case is:
struct frame
{
int size;
char buf[0];
};
union
{
struct frame f;
char padding[100 + sizeof(struct frame)];
} u;
u.frame.size = strlen(s) + 1;
strcpy(u.frame.buf, s);
-D_FORTIFY_SOURCE=2 will abort this, but -D_FORTIFY_SOURCE=1 won't.
(Yes, I know "char buf[0]" should be changed to a flexible array member
"char buf[]" to fix this, but it is just an example.)
--
Xi Ruoyao <xry111@mengyan1223.wang>
School of Aerospace Science and Technology, Xidian University
next prev parent reply other threads:[~2022-03-02 20:23 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-01 23:23 Reinoud Koornstra
2022-03-02 10:22 ` Florian Weimer
2022-03-02 19:09 ` Reinoud Koornstra
2022-03-02 19:46 ` Xi Ruoyao
2022-03-02 20:05 ` Reinoud Koornstra
2022-03-02 20:23 ` Xi Ruoyao [this message]
2022-03-02 20:45 ` Reinoud Koornstra
2022-03-11 19:01 ` Reinoud Koornstra
2022-03-12 8:19 ` Xi Ruoyao
2022-04-19 11:24 ` Florian Weimer
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