From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id 5C2443858C74; Thu,  2 Feb 2023 12:10:19 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 5C2443858C74
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1675339819;
	bh=OzgmGeDInBwatO1BAsc7eIq6fPkrsR7L6IRQYE0S5xE=;
	h=From:To:Subject:Date:From;
	b=f68M3XPbrvtHg2e7gxEYBNRNnl39FLd7PJZEb/4/hszhQqY5ga9cw040XGDitrEds
	 LuPtiSDcmXUGls6QAOh1F5XD2FnmJcQfq7kFXrJIAuWTVoJkcOr9RpeNGUHmseqx4Q
	 pAUkGZmLZO5TiXKKRh/+r+K2C+FTCtXNFIZ0xr0o=
From: "shaohua.li at inf dot ethz.ch" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug sanitizer/108637] New: ASAN at -O2 misses a
 stack-use-after-scope
Date: Thu, 02 Feb 2023 12:10:18 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: sanitizer
X-Bugzilla-Version: 13.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: shaohua.li at inf dot ethz.ch
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter cc target_milestone
Message-ID: <bug-108637-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108637

            Bug ID: 108637
           Summary: ASAN at -O2 misses a stack-use-after-scope
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: shaohua.li at inf dot ethz.ch
                CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
                    jakub at gcc dot gnu.org, kcc at gcc dot gnu.org, marxi=
n at gcc dot gnu.org
  Target Milestone: ---

For the following code, ASAN at -O2 cannot detect the stack-use-after-scope.
This happens since GCC-11. GCC-10 and below work fine.

I understand that there is a type-incompatible warning. But I believe it sh=
ould
not affect the ASAN anyway.

Compiler explorer: https://godbolt.org/z/WcbadP961

% cat a.c
char a, b, c;
short d;
int main() {
  {
    long e =3D a;
    for (; b <=3D 0; b++) {
      char *f;
      d =3D 2;
      for (; d; d--) {
        int g =3D 111;
        f =3D &g;
        if (e)
          c =3D 0;
      }
      *f +=3D 1;
      a =3D *f;
    }
  }
}
%
% gcc-tk -fsanitize=3Daddress -O2 a.c && ./a.out
%
% gcc-tk -fsanitize=3Daddress -O1 a.c && ./a.out
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
=3D=3D1=3D=3DERROR: AddressSanitizer: stack-use-after-scope on address 0x7f=
b285e00020
at pc 0x000000401272 bp 0x7ffda17739c0 sp 0x7ffda17739b8
READ of size 1 at 0x7fb285e00020 thread T0
    #0 0x401271 in main /a.c:15
    #1 0x7fb28883d082 in __libc_start_main
(/lib/x86_64-linux-gnu/libc.so.6+0x24082) (BuildId:
1878e6b475720c7c51969e69ab2d276fae6d1dee)
    #2 0x4010bd in _start (/output.s+0x4010bd) (BuildId:
cb6e8e9c15b7d8e5515d7e6b8591d2b77b5f3e21)

Address 0x7fb285e00020 is located in stack of thread T0 at offset 32 in fra=
me
    #0 0x401185 in main /a.c:3

  This frame has 1 object(s):
    [32, 36) 'g' (line 10) <=3D=3D Memory access at offset 32 is inside this
variable
HINT: this may be a false positive if your program uses some custom stack
unwind mechanism, swapcontext or vfork
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-use-after-scope /a.c:15 in main
Shadow bytes around the buggy address:
...
%=