[cairo-bugs] [Bug 101530] New: Attempting free on address which was not malloc() in cairo-clip.c:137

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Tue Jun 20 21:04:07 UTC 2017


            Bug ID: 101530
           Summary: Attempting free on address which was not malloc() in
           Product: cairo
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: general
          Assignee: chris at chris-wilson.co.uk
          Reporter: foca at salesforce.com
        QA Contact: cairo-bugs at cairographics.org

Created attachment 132101
  --> https://bugs.freedesktop.org/attachment.cgi?id=132101&action=edit
Proof of concept

There is a bug attempting free on address which was not malloc() in
127     void
128     _cairo_clip_destroy (cairo_clip_t *clip)
129     {
130         if (clip == NULL || _cairo_clip_is_all_clipped (clip))
131             return;
133         if (clip->path != NULL)
134             _cairo_clip_path_destroy (clip->path);
136         if (clip->boxes != &clip->embedded_box)
137             free (clip->boxes);

In some cases clip->boxes could be allocated but in the PoC is not allocated is
assigned to clip->embedded_box a member of the same class at
149     static cairo_clip_t *
150     _cairo_clip_intersect_rectangle_box (cairo_clip_t *clip,
151                                          const cairo_rectangle_int_t *r,
152                                          const cairo_box_t *box)
153     {
154         cairo_box_t extents_box;
155         cairo_bool_t changed = FALSE;
156         int i, j;
158         if (clip == NULL) {
159             clip = _cairo_clip_create ();
160             if (clip == NULL)
161                 return _cairo_clip_set_all_clipped (clip);
162         }
164         if (clip->num_boxes == 0) {
165             clip->boxes = &clip->embedded_box;

There is already a check in _cairo_clip_destroy to avoid similar cases:
136         if (clip->boxes != &clip->embedded_box)

But with the PoC the clip where the embedded_box is comming is different the
the clip being destroyed.

This bug was found when using a poppler util, pdftocairo. A PoC is attached. To
reproduce the bug use:
pdftocairo -svg PoC.pdf

This vulnerability has been found by Offensive Research at Salesforce.com:
Alberto Garcia (@algillera), Francisco Oca (@francisco_oca) & Suleman Ali

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