fix use after free in font caching algorithm - st - simple terminal
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---
DIR commit a8cb8e94547d7e31441d2444e8a196415e3e4c1f
DIR parent e85b6b64660214121164ea97fb098eaa4935f7db
HTML Author: magras <dr.magras@gmail.com>
Date: Thu, 28 Feb 2019 04:56:01 +0300
fix use after free in font caching algorithm
Current font caching algorithm contains a use after free error. A font
removed from `frc` might be still listed in `wx.specbuf`. It will lead
to a crash inside `XftDrawGlyphFontSpec()`.
Steps to reproduce:
$ st -f 'Misc Tamsyn:scalable=false'
$ curl https://www.cl.cam.ac.uk/~mgk25/ucs/examples/UTF-8-demo.txt
Of course, result depends on fonts installed on a system and fontconfig.
In my case, I'm getting consistent segfaults with different fonts.
I replaced a fixed array with a simple unbounded buffer with a constant
growth rate. Cache starts with a capacity of 0, gets increments by 16,
and never shrinks. On my machine after `cat UTF-8-demo.txt` buffer
reaches a capacity of 192. During casual use capacity stays at 0.
Diffstat:
M x.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
---
DIR diff --git a/x.c b/x.c
@@ -226,8 +226,9 @@ typedef struct {
} Fontcache;
/* Fontcache is an array now. A new font will be appended to the array. */
-static Fontcache frc[16];
+static Fontcache *frc = NULL;
static int frclen = 0;
+static int frccap = 0;
static char *usedfont = NULL;
static double usedfontsize = 0;
static double defaultfontsize = 0;
@@ -1244,12 +1245,14 @@ xmakeglyphfontspecs(XftGlyphFontSpec *specs, const Glyph *glyphs, int len, int x
fcpattern, &fcres);
/*
- * Overwrite or create the new cache entry.
+ * Allocate memory for the new cache entry.
*/
- if (frclen >= LEN(frc)) {
- frclen = LEN(frc) - 1;
- XftFontClose(xw.dpy, frc[frclen].font);
- frc[frclen].unicodep = 0;
+ if (frclen >= frccap) {
+ frccap += 16;
+ if (!frc)
+ frc = xmalloc(frccap * sizeof(Fontcache));
+ else
+ frc = xrealloc(frc, frccap * sizeof(Fontcache));
}
frc[frclen].font = XftFontOpenPattern(xw.dpy,