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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug analyzer/107534] New: Analyzer should flag shallow copies of
 resources
Date: Sat, 05 Nov 2022 09:58:01 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: analyzer
X-Bugzilla-Version: 13.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: redi at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: dmalcolm at gcc dot gnu.org
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107534

            Bug ID: 107534
           Summary: Analyzer should flag shallow copies of resources
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: analyzer
          Assignee: dmalcolm at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
            Blocks: 97110
  Target Milestone: ---

As shown in PR 94355 comment 11, this code reports a use-after-free (and a
spurious leak and spurious null deref):

struct S {
    S() { p =3D new int(); }
    ~S() { delete p; }
    int* p =3D nullptr;
};

int main() {
    S s;
    S ss =3D s;
}

Ideally the copy construction of 'ss' would flag that we end up with two ow=
ners
of the heap pointer. The new object should either make a deep copy (allocat=
e a
new object as a copy of *s.p) or should clear the source so it's left empty
(which would require a move constructor, not just the trivial copy construc=
tor
that makes the shallow copy here).

In other words, rather than flagging three symptoms, flag the cause. The ty=
pe
manages dynamic resources but doesn't have a user-provided copy or move
constructor and so manages them unsafely.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97110
[Bug 97110] [meta-bug] tracker bug for supporting C++ in -fanalyzer=