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List: kde-frameworks-devel
Subject: Re: Review Request 126507: Fix leaked file description and potential use-after-free in kdelibs4suppo
From: "David Faure" <faure () kde ! org>
Date: 2016-01-02 11:30:05
Message-ID: 20160102113005.30660.34768 () mimi ! kde ! org
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https://git.reviewboard.kde.org/r/126507/#review90439
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src/kdeui/k4style.cpp (line 1176)
<https://git.reviewboard.kde.org/r/126507/#comment61851>
The double-lookup looks slow and unnecessary.
contains + *object doesn't give you anything that object (followed by a \
dereference if not null) gives you.
If the fear is concurrent access, then contains + *object can still dereference a \
null pointer anyway.
But K4Style runs in the GUI thread always anyway. So I would call object(), put \
that into a pointer, and then if not null, make a copy into a value. This avoids the \
double lookup.
- David Faure
On Jan. 2, 2016, 1:55 a.m., Michael Pyne wrote:
>
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://git.reviewboard.kde.org/r/126507/
> -----------------------------------------------------------
>
> (Updated Jan. 2, 2016, 1:55 a.m.)
>
>
> Review request for KDE Frameworks.
>
>
> Repository: kdelibs4support
>
>
> Description
> -------
>
> Fix a couple of Coverity issues:
>
> 1. CID 1175508; file descriptors used in KLockFile could be leaked in
> error conditions. Even when KLockFile sets mustCloseFd, the dtor's impl
> also checks that the lock has been taken, which is only considered true
> if LockOK had been returned in our lock function. Instead close() the fd
> ourselves unless we make it to LockOK.
>
> 2. CID 1175555; The standard mis-use of QCache. QCache::insert can, in
> theory, delete our object as soon as we insert it into cache, so we have
> to check for that. Even ::contains() and ::object() can be risky (the
> pointers returned by object() have no lifetime guarantee), but since
> this is GUI code I assume it's only used single-threaded and not
> re-entrant. Otherwise we'd need even more paranoia...
>
>
> Diffs
> -----
>
> src/kdecore/klockfile_unix.cpp 67283a5
> src/kdeui/k4style.cpp a1a2ab1
>
> Diff: https://git.reviewboard.kde.org/r/126507/diff/
>
>
> Testing
> -------
>
> Everything builds and appears to still work, though it's hard to test K4Style as \
> I'm not sure what uses it right at this point.
>
> Thanks,
>
> Michael Pyne
>
>
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This is an automatically generated e-mail. To reply, visit:
<a href="https://git.reviewboard.kde.org/r/126507/">https://git.reviewboard.kde.org/r/126507/</a>
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<th colspan="4" bgcolor="#F0F0F0" style="border-bottom: 1px solid #C0C0C0; \
font-size: 9pt; padding: 4px 8px; text-align: left;"> <a \
href="https://git.reviewboard.kde.org/r/126507/diff/2/?file=428212#file428212line1176" \
style="color: black; font-weight: bold; text-decoration: \
underline;">src/kdeui/k4style.cpp</a> <span style="font-weight: normal;">
(Diff revision 2)
</span>
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<td colspan="4"><pre style="font-size: 8pt; line-height: 140%; margin: 0; ">void \
K4Style::drawPrimitive(PrimitiveElement elem, const QStyleOption *option, QPainter \
*painter, const QWidget *widget) const</pre></td>
</tr>
</tbody>
<tbody>
<tr>
<th bgcolor="#e9eaa8" style="border-right: 1px solid #C0C0C0;" \
align="right"><font size="2">1176</font></th> <td bgcolor="#fdfebc" width="50%"><pre \
style="font-size: 8pt; line-height: 140%; margin: 0; "> <span \
class="k">if</span> <span class="p">(</span><span class="o">!</span><span \
class="n">tiles</span> <span class="o">&&</span> <span \
class="n">hasSolidBackground</span><span class="p">)</span> <span \
class="p">{</span></pre></td> <th bgcolor="#e9eaa8" style="border-left: 1px solid \
#C0C0C0; border-right: 1px solid #C0C0C0;" align="right"><font \
size="2">1176</font></th> <td bgcolor="#fdfebc" width="50%"><pre style="font-size: \
8pt; line-height: 140%; margin: 0; "> <span class="kt">bool</span> <span \
class="n">hasCachedTiles</span> <span class="o">=</span> <span \
class="n">d</span><span class="o">-></span><span \
class="n">selectionCache</span><span class="p">.</span><span \
class="n">contains</span><span class="p">(</span><span class="n">key</span><span \
class="p">);</span></pre></td> </tr>
</tbody>
</table>
<div style="margin-left: 2em;">
<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: \
-pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">The double-lookup looks \
slow and unnecessary. contains + *object doesn't give you anything that object \
(followed by a dereference if not null) gives you.
If the fear is concurrent access, then contains + *object can still dereference a \
null pointer anyway.
But K4Style runs in the GUI thread always anyway. So I would call object(), put that \
into a pointer, and then if not null, make a copy into a value. This avoids the \
double lookup.</pre> </div>
</div>
<br />
<p>- David Faure</p>
<br />
<p>On January 2nd, 2016, 1:55 a.m. UTC, Michael Pyne wrote:</p>
<table bgcolor="#fefadf" width="100%" cellspacing="0" cellpadding="12" style="border: \
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<td>
<div>Review request for KDE Frameworks.</div>
<div>By Michael Pyne.</div>
<p style="color: grey;"><i>Updated Jan. 2, 2016, 1:55 a.m.</i></p>
<div style="margin-top: 1.5em;">
<b style="color: #575012; font-size: 10pt;">Repository: </b>
kdelibs4support
</div>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Description </h1>
<table width="100%" bgcolor="#ffffff" cellspacing="0" cellpadding="10" \
style="border: 1px solid #b8b5a0"> <tr>
<td>
<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;"><p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">Fix a couple of Coverity issues:</p> <ol \
style="padding: 0;text-rendering: inherit;margin: 0 0 0 2em;line-height: \
inherit;white-space: normal;"> <li style="padding: 0;text-rendering: inherit;margin: \
0;line-height: inherit;white-space: normal;"> <p style="padding: 0;text-rendering: \
inherit;margin: 0;line-height: inherit;white-space: inherit;">CID 1175508; file \
descriptors used in KLockFile could be leaked in error conditions. Even when \
KLockFile sets mustCloseFd, the dtor's impl also checks that the lock has been taken, \
which is only considered true if LockOK had been returned in our lock function. \
Instead close() the fd ourselves unless we make it to LockOK.</p>
</li>
<li style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: normal;"> <p style="padding: 0;text-rendering: inherit;margin: \
0;line-height: inherit;white-space: inherit;">CID 1175555; The standard mis-use of \
QCache. QCache::insert can, in theory, delete our object as soon as we insert it into \
cache, so we have to check for that. Even ::contains() and ::object() can be risky \
(the pointers returned by object() have no lifetime guarantee), but since
this is GUI code I assume it's only used single-threaded and not
re-entrant. Otherwise we'd need even more paranoia...</p>
</li>
</ol></pre>
</td>
</tr>
</table>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Testing </h1>
<table width="100%" bgcolor="#ffffff" cellspacing="0" cellpadding="10" style="border: \
1px solid #b8b5a0"> <tr>
<td>
<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;"><p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">Everything builds and appears to still work, though \
it's hard to test K4Style as I'm not sure what uses it right at this point.</p></pre> \
</td> </tr>
</table>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Diffs</b> </h1>
<ul style="margin-left: 3em; padding-left: 0;">
<li>src/kdecore/klockfile_unix.cpp <span style="color: grey">(67283a5)</span></li>
<li>src/kdeui/k4style.cpp <span style="color: grey">(a1a2ab1)</span></li>
</ul>
<p><a href="https://git.reviewboard.kde.org/r/126507/diff/" style="margin-left: \
3em;">View Diff</a></p>
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