Guard against underflow when adjusting length (#421)
* Guard against underflow when adjusting length
With the fuzz-testcase in mozilla bug 1295299, we end up with a recursed lookup that removes 3 items, when `match_positions[idx]` is 0, which results in (unsigned) `end` wrapping to a huge value.
Making `end` a signed int is probably the simplest route to a fix.
Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1295299.
* Add testcase for #421.
diff --git a/src/hb-ot-layout-gsubgpos-private.hh b/src/hb-ot-layout-gsubgpos-private.hh
index b7a0122..0c42352 100644
--- a/src/hb-ot-layout-gsubgpos-private.hh
+++ b/src/hb-ot-layout-gsubgpos-private.hh
@@ -959,7 +959,7 @@
TRACE_APPLY (NULL);
hb_buffer_t *buffer = c->buffer;
- unsigned int end;
+ int end;
/* All positions are distance from beginning of *output* buffer.
* Adjust. */
@@ -998,8 +998,8 @@
/* Recursed lookup changed buffer len. Adjust. */
- end = int (end) + delta;
- if (end <= match_positions[idx])
+ end += delta;
+ if (end <= int (match_positions[idx]))
{
/* End might end up being smaller than match_positions[idx] if the recursed
* lookup ended up removing many items, more than we have had matched.
diff --git a/test/shaping/fonts/sha1sum/558661aa659912f4d30ecd27bd09835171a8e2b0.ttf b/test/shaping/fonts/sha1sum/558661aa659912f4d30ecd27bd09835171a8e2b0.ttf
new file mode 100644
index 0000000..5d72fdf
--- /dev/null
+++ b/test/shaping/fonts/sha1sum/558661aa659912f4d30ecd27bd09835171a8e2b0.ttf
Binary files differ
diff --git a/test/shaping/tests/fuzzed.tests b/test/shaping/tests/fuzzed.tests
index 771ac2b..d9bace3 100644
--- a/test/shaping/tests/fuzzed.tests
+++ b/test/shaping/tests/fuzzed.tests
@@ -10,3 +10,4 @@
fonts/sha1sum/fab39d60d758cb586db5a504f218442cd1395725.ttf:--font-funcs=ot:U+0041,U+0041:[gid0=0+1000|gid0=1+1000]
fonts/sha1sum/205edd09bd3d141cc9580f650109556cc28b22cb.ttf:--font-funcs=ot:U+0041:[gid0=0+1000]
fonts/sha1sum/217a934cfe15c548b572c203dceb2befdf026462.ttf:--font-funcs=ot:U+0061,U+0061,U+0061:[]
+fonts/sha1sum/558661aa659912f4d30ecd27bd09835171a8e2b0.ttf:--font-funcs=ot:U+FFFD,U+E0100,U+FFFD,U+E0010:[]
