From 419505ab0163edd2a8dfb73b6fefb737d42f734e Mon Sep 17 00:00:00 2001 From: Marc Mutz Date: Wed, 4 Aug 2021 10:17:11 +0200 Subject: [PATCH] QXpmHandler: fix re-entrancy bug in xpm_color_name MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The xpm_color_name() function returned a pointer to a function-static buffer. This is infamously non-reentrant, and an actual problem, because we explicitly allow QImage operations (incl. saving to an .xpm) from non-GUI-threads. Fix by using the CSS pattern (Caller-Supplied Storage; also used in the QAnyStringView(char32_t) and QAnyStringView(QStringBuilder) ctors) to force the caller to allocate storage in its own stack frame. As a consequence, we re-gain re-entrancy, but the returned pointer is now only valid until the end of the full-expression, which isn't a problem, as all callers immediately pass the result to a consumer (asprintf() or QByteArray). [ChangeLog][QtGui][QImage] Fixed a race condition when concurrently writing .xpm files. Change-Id: I36d7173d53839a52f5cdf58324474c1b32c71f33 Reviewed-by: MÃ¥rten Nordheim (cherry picked from commit 73fabadcee71af858388fb245fccf4e96d4ead4e) --- src/gui/image/qxpmhandler.cpp | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/src/gui/image/qxpmhandler.cpp b/src/gui/image/qxpmhandler.cpp index f5fe6cb7ea0..1bd9531e9b0 100644 --- a/src/gui/image/qxpmhandler.cpp +++ b/src/gui/image/qxpmhandler.cpp @@ -49,6 +49,7 @@ #include #include +#include QT_BEGIN_NAMESPACE @@ -1055,15 +1056,23 @@ bool qt_read_xpm_image_or_array(QIODevice *device, const char * const * source, return read_xpm_body(device, source, index, state, cpp, ncols, w, h, image); } -static const char* xpm_color_name(int cpp, int index) +namespace { +template +struct CharBuffer : std::array +{ + CharBuffer() {} // avoid value-initializing the whole array +}; +} + +static const char* xpm_color_name(int cpp, int index, CharBuffer<5> && returnable = {}) { - static char returnable[5]; static const char code[] = ".#abcdefghijklmnopqrstuvwxyzABCD" "EFGHIJKLMNOPQRSTUVWXYZ0123456789"; // cpp is limited to 4 and index is limited to 64^cpp if (cpp > 1) { if (cpp > 2) { if (cpp > 3) { + returnable[4] = '\0'; returnable[3] = code[index % 64]; index /= 64; } else @@ -1083,7 +1092,7 @@ static const char* xpm_color_name(int cpp, int index) returnable[1] = '\0'; returnable[0] = code[index]; - return returnable; + return returnable.data(); }