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From 8708b9e081192786c027bb7f5f23d76dbe5c19e8 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Mon, 6 Feb 2023 14:51:25 -0700
Subject: [PATCH] [GPOS] Avoid O(n^2) behavior in mark-attachment
Upstream-Status: Backport from [https://github.com/harfbuzz/harfbuzz/commit/8708b9e081192786c027bb7f5f23d76dbe5c19e8]
Comment1: The Original Patch [https://github.com/harfbuzz/harfbuzz/commit/85be877925ddbf34f74a1229f3ca1716bb6170dc] causes regression and was reverted. This Patch completes the fix.
CVE: CVE-2023-25193
Signed-off-by: Siddharth Doshi <sdoshi@mvista.com>
---
src/OT/Layout/GPOS/MarkBasePosFormat1.hh | 76 +++++++++++++++---------
src/OT/Layout/GPOS/MarkLigPosFormat1.hh | 24 ++++++--
src/hb-ot-layout-gsubgpos.hh | 5 +-
3 files changed, 69 insertions(+), 36 deletions(-)
diff --git a/src/OT/Layout/GPOS/MarkBasePosFormat1.hh b/src/OT/Layout/GPOS/MarkBasePosFormat1.hh
index ebb8c31..73839a4 100644
--- a/src/OT/Layout/GPOS/MarkBasePosFormat1.hh
+++ b/src/OT/Layout/GPOS/MarkBasePosFormat1.hh
@@ -90,6 +90,25 @@ struct MarkBasePosFormat1_2
const Coverage &get_coverage () const { return this+markCoverage; }
+ static inline bool accept (hb_buffer_t *buffer, unsigned idx)
+ {
+ /* We only want to attach to the first of a MultipleSubst sequence.
+ * https://github.com/harfbuzz/harfbuzz/issues/740
+ * Reject others...
+ * ...but stop if we find a mark in the MultipleSubst sequence:
+ * https://github.com/harfbuzz/harfbuzz/issues/1020 */
+ return !_hb_glyph_info_multiplied (&buffer->info[idx]) ||
+ 0 == _hb_glyph_info_get_lig_comp (&buffer->info[idx]) ||
+ (idx == 0 ||
+ _hb_glyph_info_is_mark (&buffer->info[idx - 1]) ||
+ !_hb_glyph_info_multiplied (&buffer->info[idx - 1]) ||
+ _hb_glyph_info_get_lig_id (&buffer->info[idx]) !=
+ _hb_glyph_info_get_lig_id (&buffer->info[idx - 1]) ||
+ _hb_glyph_info_get_lig_comp (&buffer->info[idx]) !=
+ _hb_glyph_info_get_lig_comp (&buffer->info[idx - 1]) + 1
+ );
+ }
+
bool apply (hb_ot_apply_context_t *c) const
{
TRACE_APPLY (this);
@@ -97,48 +116,47 @@ struct MarkBasePosFormat1_2
unsigned int mark_index = (this+markCoverage).get_coverage (buffer->cur().codepoint);
if (likely (mark_index == NOT_COVERED)) return_trace (false);
- /* Now we search backwards for a non-mark glyph */
+ /* Now we search backwards for a non-mark glyph.
+ * We don't use skippy_iter.prev() to avoid O(n^2) behavior. */
+
hb_ot_apply_context_t::skipping_iterator_t &skippy_iter = c->iter_input;
- skippy_iter.reset (buffer->idx, 1);
skippy_iter.set_lookup_props (LookupFlag::IgnoreMarks);
- do {
- unsigned unsafe_from;
- if (!skippy_iter.prev (&unsafe_from))
+
+ unsigned j;
+ for (j = buffer->idx; j > c->last_base_until; j--)
+ {
+ auto match = skippy_iter.match (buffer->info[j - 1]);
+ if (match == skippy_iter.MATCH)
{
- buffer->unsafe_to_concat_from_outbuffer (unsafe_from, buffer->idx + 1);
- return_trace (false);
+ if (!accept (buffer, j - 1))
+ match = skippy_iter.SKIP;
}
+ if (match == skippy_iter.MATCH)
+ {
+ c->last_base = (signed) j - 1;
+ break;
+ }
+ }
+ c->last_base_until = buffer->idx;
+ if (c->last_base == -1)
+ {
+ buffer->unsafe_to_concat_from_outbuffer (0, buffer->idx + 1);
+ return_trace (false);
+ }
- /* We only want to attach to the first of a MultipleSubst sequence.
- * https://github.com/harfbuzz/harfbuzz/issues/740
- * Reject others...
- * ...but stop if we find a mark in the MultipleSubst sequence:
- * https://github.com/harfbuzz/harfbuzz/issues/1020 */
- if (!_hb_glyph_info_multiplied (&buffer->info[skippy_iter.idx]) ||
- 0 == _hb_glyph_info_get_lig_comp (&buffer->info[skippy_iter.idx]) ||
- (skippy_iter.idx == 0 ||
- _hb_glyph_info_is_mark (&buffer->info[skippy_iter.idx - 1]) ||
- !_hb_glyph_info_multiplied (&buffer->info[skippy_iter.idx - 1]) ||
- _hb_glyph_info_get_lig_id (&buffer->info[skippy_iter.idx]) !=
- _hb_glyph_info_get_lig_id (&buffer->info[skippy_iter.idx - 1]) ||
- _hb_glyph_info_get_lig_comp (&buffer->info[skippy_iter.idx]) !=
- _hb_glyph_info_get_lig_comp (&buffer->info[skippy_iter.idx - 1]) + 1
- ))
- break;
- skippy_iter.reject ();
- } while (true);
+ unsigned idx = (unsigned) c->last_base;
/* Checking that matched glyph is actually a base glyph by GDEF is too strong; disabled */
- //if (!_hb_glyph_info_is_base_glyph (&buffer->info[skippy_iter.idx])) { return_trace (false); }
+ //if (!_hb_glyph_info_is_base_glyph (&buffer->info[idx])) { return_trace (false); }
- unsigned int base_index = (this+baseCoverage).get_coverage (buffer->info[skippy_iter.idx].codepoint);
+ unsigned int base_index = (this+baseCoverage).get_coverage (buffer->info[idx].codepoint);
if (base_index == NOT_COVERED)
{
- buffer->unsafe_to_concat_from_outbuffer (skippy_iter.idx, buffer->idx + 1);
+ buffer->unsafe_to_concat_from_outbuffer (idx, buffer->idx + 1);
return_trace (false);
}
- return_trace ((this+markArray).apply (c, mark_index, base_index, this+baseArray, classCount, skippy_iter.idx));
+ return_trace ((this+markArray).apply (c, mark_index, base_index, this+baseArray, classCount, idx));
}
bool subset (hb_subset_context_t *c) const
diff --git a/src/OT/Layout/GPOS/MarkLigPosFormat1.hh b/src/OT/Layout/GPOS/MarkLigPosFormat1.hh
index 1a80212..4471871 100644
--- a/src/OT/Layout/GPOS/MarkLigPosFormat1.hh
+++ b/src/OT/Layout/GPOS/MarkLigPosFormat1.hh
@@ -100,20 +100,32 @@ struct MarkLigPosFormat1_2
if (likely (mark_index == NOT_COVERED)) return_trace (false);
/* Now we search backwards for a non-mark glyph */
+
hb_ot_apply_context_t::skipping_iterator_t &skippy_iter = c->iter_input;
- skippy_iter.reset (buffer->idx, 1);
skippy_iter.set_lookup_props (LookupFlag::IgnoreMarks);
- unsigned unsafe_from;
- if (!skippy_iter.prev (&unsafe_from))
+
+ unsigned j;
+ for (j = buffer->idx; j > c->last_base_until; j--)
{
- buffer->unsafe_to_concat_from_outbuffer (unsafe_from, buffer->idx + 1);
+ auto match = skippy_iter.match (buffer->info[j - 1]);
+ if (match == skippy_iter.MATCH)
+ {
+ c->last_base = (signed) j - 1;
+ break;
+ }
+ }
+ c->last_base_until = buffer->idx;
+ if (c->last_base == -1)
+ {
+ buffer->unsafe_to_concat_from_outbuffer (0, buffer->idx + 1);
return_trace (false);
}
+ j = (unsigned) c->last_base;
+
/* Checking that matched glyph is actually a ligature by GDEF is too strong; disabled */
- //if (!_hb_glyph_info_is_ligature (&buffer->info[skippy_iter.idx])) { return_trace (false); }
+ //if (!_hb_glyph_info_is_ligature (&buffer->info[j])) { return_trace (false); }
- unsigned int j = skippy_iter.idx;
unsigned int lig_index = (this+ligatureCoverage).get_coverage (buffer->info[j].codepoint);
if (lig_index == NOT_COVERED)
{
diff --git a/src/hb-ot-layout-gsubgpos.hh b/src/hb-ot-layout-gsubgpos.hh
index 04b823e..dc3c4b6 100644
--- a/src/hb-ot-layout-gsubgpos.hh
+++ b/src/hb-ot-layout-gsubgpos.hh
@@ -701,6 +701,9 @@ struct hb_ot_apply_context_t :
uint32_t random_state = 1;
unsigned new_syllables = (unsigned) -1;
+ signed last_base = -1; // GPOS uses
+ unsigned last_base_until = 0; // GPOS uses
+
hb_ot_apply_context_t (unsigned int table_index_,
hb_font_t *font_,
hb_buffer_t *buffer_) :
@@ -738,7 +741,7 @@ struct hb_ot_apply_context_t :
iter_context.init (this, true);
}
- void set_lookup_mask (hb_mask_t mask) { lookup_mask = mask; init_iters (); }
+ void set_lookup_mask (hb_mask_t mask) { lookup_mask = mask; last_base = -1; last_base_until = 0; init_iters (); }
void set_auto_zwj (bool auto_zwj_) { auto_zwj = auto_zwj_; init_iters (); }
void set_auto_zwnj (bool auto_zwnj_) { auto_zwnj = auto_zwnj_; init_iters (); }
void set_per_syllable (bool per_syllable_) { per_syllable = per_syllable_; init_iters (); }
--
2.25.1
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