2019-03-30 22:59:40 +01:00
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/*
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* Copyright © 2007,2008,2009,2010 Red Hat, Inc.
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* Copyright © 2012,2018 Google, Inc.
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*
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* This is part of HarfBuzz, a text shaping library.
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*
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* Permission is hereby granted, without written agreement and without
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* license or royalty fees, to use, copy, modify, and distribute this
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* software and its documentation for any purpose, provided that the
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* above copyright notice and the following two paragraphs appear in
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* all copies of this software.
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*
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* IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
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* DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
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* ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
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* IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
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* DAMAGE.
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*
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* THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
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* BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
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* FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
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* ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
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* PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
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*
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* Red Hat Author(s): Behdad Esfahbod
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* Google Author(s): Behdad Esfahbod
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*/
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#ifndef HB_SANITIZE_HH
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#define HB_SANITIZE_HH
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#include "hb.hh"
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#include "hb-blob.hh"
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#include "hb-dispatch.hh"
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/*
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* Sanitize
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*
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*
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* === Introduction ===
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*
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* The sanitize machinery is at the core of our zero-cost font loading. We
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* mmap() font file into memory and create a blob out of it. Font subtables
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* are returned as a readonly sub-blob of the main font blob. These table
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* blobs are then sanitized before use, to ensure invalid memory access does
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* not happen. The toplevel sanitize API use is like, eg. to load the 'head'
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* table:
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*
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* hb_blob_t *head_blob = hb_sanitize_context_t ().reference_table<OT::head> (face);
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*
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* The blob then can be converted to a head table struct with:
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*
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* const head *head_table = head_blob->as<head> ();
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*
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* What the reference_table does is, to call hb_face_reference_table() to load
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* the table blob, sanitize it and return either the sanitized blob, or empty
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* blob if sanitization failed. The blob->as() function returns the null
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* object of its template type argument if the blob is empty. Otherwise, it
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* just casts the blob contents to the desired type.
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*
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* Sanitizing a blob of data with a type T works as follows (with minor
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* simplification):
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*
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* - Cast blob content to T*, call sanitize() method of it,
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* - If sanitize succeeded, return blob.
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* - Otherwise, if blob is not writable, try making it writable,
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* or copy if cannot be made writable in-place,
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* - Call sanitize() again. Return blob if sanitize succeeded.
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* - Return empty blob otherwise.
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*
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*
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* === The sanitize() contract ===
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*
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* The sanitize() method of each object type shall return true if it's safe to
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2020-12-30 22:08:40 +01:00
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* call other methods of the object, and %false otherwise.
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2019-03-30 22:59:40 +01:00
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*
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* Note that what sanitize() checks for might align with what the specification
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* describes as valid table data, but does not have to be. In particular, we
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* do NOT want to be pedantic and concern ourselves with validity checks that
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* are irrelevant to our use of the table. On the contrary, we want to be
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* lenient with error handling and accept invalid data to the extent that it
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* does not impose extra burden on us.
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*
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* Based on the sanitize contract, one can see that what we check for depends
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* on how we use the data in other table methods. Ie. if other table methods
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* assume that offsets do NOT point out of the table data block, then that's
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* something sanitize() must check for (GSUB/GPOS/GDEF/etc work this way). On
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* the other hand, if other methods do such checks themselves, then sanitize()
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* does not have to bother with them (glyf/local work this way). The choice
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* depends on the table structure and sanitize() performance. For example, to
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* check glyf/loca offsets in sanitize() would cost O(num-glyphs). We try hard
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* to avoid such costs during font loading. By postponing such checks to the
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* actual glyph loading, we reduce the sanitize cost to O(1) and total runtime
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* cost to O(used-glyphs). As such, this is preferred.
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*
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* The same argument can be made re GSUB/GPOS/GDEF, but there, the table
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* structure is so complicated that by checking all offsets at sanitize() time,
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* we make the code much simpler in other methods, as offsets and referenced
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* objects do not need to be validated at each use site.
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*/
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/* This limits sanitizing time on really broken fonts. */
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#ifndef HB_SANITIZE_MAX_EDITS
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#define HB_SANITIZE_MAX_EDITS 32
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#endif
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#ifndef HB_SANITIZE_MAX_OPS_FACTOR
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#define HB_SANITIZE_MAX_OPS_FACTOR 8
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#endif
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#ifndef HB_SANITIZE_MAX_OPS_MIN
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#define HB_SANITIZE_MAX_OPS_MIN 16384
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#endif
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#ifndef HB_SANITIZE_MAX_OPS_MAX
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#define HB_SANITIZE_MAX_OPS_MAX 0x3FFFFFFF
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#endif
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2021-01-24 21:30:06 +01:00
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#ifndef HB_SANITIZE_MAX_SUBTABLES
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#define HB_SANITIZE_MAX_SUBTABLES 0x4000
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2020-03-02 20:11:08 +01:00
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#endif
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2019-03-30 22:59:40 +01:00
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struct hb_sanitize_context_t :
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hb_dispatch_context_t<hb_sanitize_context_t, bool, HB_DEBUG_SANITIZE>
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{
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hb_sanitize_context_t () :
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start (nullptr), end (nullptr),
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2020-03-02 20:11:08 +01:00
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max_ops (0), max_subtables (0),
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2019-03-30 22:59:40 +01:00
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writable (false), edit_count (0),
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blob (nullptr),
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num_glyphs (65536),
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num_glyphs_set (false) {}
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const char *get_name () { return "SANITIZE"; }
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template <typename T, typename F>
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bool may_dispatch (const T *obj HB_UNUSED, const F *format)
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{ return format->sanitize (this); }
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static return_t default_return_value () { return true; }
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static return_t no_dispatch_return_value () { return false; }
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bool stop_sublookup_iteration (const return_t r) const { return !r; }
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2020-03-02 20:11:08 +01:00
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bool visit_subtables (unsigned count)
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{
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max_subtables += count;
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2021-01-24 21:30:06 +01:00
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return max_subtables < HB_SANITIZE_MAX_SUBTABLES;
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2020-03-02 20:11:08 +01:00
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}
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2019-05-05 18:54:58 +02:00
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private:
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template <typename T, typename ...Ts> auto
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2019-05-08 05:58:43 +02:00
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_dispatch (const T &obj, hb_priority<1>, Ts&&... ds) HB_AUTO_RETURN
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2019-05-05 18:54:58 +02:00
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( obj.sanitize (this, hb_forward<Ts> (ds)...) )
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template <typename T, typename ...Ts> auto
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2019-05-08 05:58:43 +02:00
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_dispatch (const T &obj, hb_priority<0>, Ts&&... ds) HB_AUTO_RETURN
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2019-05-05 18:54:58 +02:00
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( obj.dispatch (this, hb_forward<Ts> (ds)...) )
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public:
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template <typename T, typename ...Ts> auto
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2019-05-08 05:58:43 +02:00
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dispatch (const T &obj, Ts&&... ds) HB_AUTO_RETURN
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2019-05-05 18:54:58 +02:00
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( _dispatch (obj, hb_prioritize, hb_forward<Ts> (ds)...) )
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2019-03-30 22:59:40 +01:00
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void init (hb_blob_t *b)
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{
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this->blob = hb_blob_reference (b);
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this->writable = false;
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}
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void set_num_glyphs (unsigned int num_glyphs_)
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{
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num_glyphs = num_glyphs_;
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num_glyphs_set = true;
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}
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unsigned int get_num_glyphs () { return num_glyphs; }
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void set_max_ops (int max_ops_) { max_ops = max_ops_; }
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template <typename T>
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void set_object (const T *obj)
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{
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reset_object ();
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if (!obj) return;
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const char *obj_start = (const char *) obj;
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if (unlikely (obj_start < this->start || this->end <= obj_start))
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this->start = this->end = nullptr;
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else
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{
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this->start = obj_start;
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2019-05-08 08:28:22 +02:00
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this->end = obj_start + hb_min (size_t (this->end - obj_start), obj->get_size ());
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2019-03-30 22:59:40 +01:00
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}
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}
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void reset_object ()
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{
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this->start = this->blob->data;
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this->end = this->start + this->blob->length;
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assert (this->start <= this->end); /* Must not overflow. */
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}
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void start_processing ()
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{
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reset_object ();
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2019-12-17 02:58:51 +01:00
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if (unlikely (hb_unsigned_mul_overflows (this->end - this->start, HB_SANITIZE_MAX_OPS_FACTOR)))
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this->max_ops = HB_SANITIZE_MAX_OPS_MAX;
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else
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2020-03-04 08:48:19 +01:00
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this->max_ops = hb_clamp ((unsigned) (this->end - this->start) * HB_SANITIZE_MAX_OPS_FACTOR,
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(unsigned) HB_SANITIZE_MAX_OPS_MIN,
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(unsigned) HB_SANITIZE_MAX_OPS_MAX);
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2019-03-30 22:59:40 +01:00
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this->edit_count = 0;
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this->debug_depth = 0;
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DEBUG_MSG_LEVEL (SANITIZE, start, 0, +1,
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"start [%p..%p] (%lu bytes)",
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this->start, this->end,
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(unsigned long) (this->end - this->start));
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}
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void end_processing ()
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{
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DEBUG_MSG_LEVEL (SANITIZE, this->start, 0, -1,
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"end [%p..%p] %u edit requests",
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this->start, this->end, this->edit_count);
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hb_blob_destroy (this->blob);
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this->blob = nullptr;
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this->start = this->end = nullptr;
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}
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2019-05-11 01:01:39 +02:00
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unsigned get_edit_count () { return edit_count; }
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2019-03-30 22:59:40 +01:00
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bool check_range (const void *base,
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unsigned int len) const
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{
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const char *p = (const char *) base;
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bool ok = !len ||
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(this->start <= p &&
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p <= this->end &&
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(unsigned int) (this->end - p) >= len &&
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this->max_ops-- > 0);
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DEBUG_MSG_LEVEL (SANITIZE, p, this->debug_depth+1, 0,
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"check_range [%p..%p]"
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" (%d bytes) in [%p..%p] -> %s",
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p, p + len, len,
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this->start, this->end,
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ok ? "OK" : "OUT-OF-RANGE");
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return likely (ok);
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}
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template <typename T>
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bool check_range (const T *base,
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unsigned int a,
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unsigned int b) const
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{
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return !hb_unsigned_mul_overflows (a, b) &&
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this->check_range (base, a * b);
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}
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template <typename T>
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bool check_range (const T *base,
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unsigned int a,
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unsigned int b,
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unsigned int c) const
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{
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return !hb_unsigned_mul_overflows (a, b) &&
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this->check_range (base, a * b, c);
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}
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template <typename T>
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bool check_array (const T *base, unsigned int len) const
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{
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return this->check_range (base, len, hb_static_size (T));
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}
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template <typename T>
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bool check_array (const T *base,
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unsigned int a,
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unsigned int b) const
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{
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return this->check_range (base, a, b, hb_static_size (T));
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}
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template <typename Type>
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bool check_struct (const Type *obj) const
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{ return likely (this->check_range (obj, obj->min_size)); }
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bool may_edit (const void *base, unsigned int len)
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{
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if (this->edit_count >= HB_SANITIZE_MAX_EDITS)
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return false;
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const char *p = (const char *) base;
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this->edit_count++;
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DEBUG_MSG_LEVEL (SANITIZE, p, this->debug_depth+1, 0,
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"may_edit(%u) [%p..%p] (%d bytes) in [%p..%p] -> %s",
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this->edit_count,
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p, p + len, len,
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this->start, this->end,
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this->writable ? "GRANTED" : "DENIED");
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return this->writable;
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
template <typename Type, typename ValueType>
|
|
|
|
|
bool try_set (const Type *obj, const ValueType &v)
|
|
|
|
|
{
|
|
|
|
|
if (this->may_edit (obj, hb_static_size (Type)))
|
|
|
|
|
{
|
|
|
|
|
* const_cast<Type *> (obj) = v;
|
|
|
|
|
return true;
|
|
|
|
|
}
|
|
|
|
|
return false;
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
template <typename Type>
|
|
|
|
|
hb_blob_t *sanitize_blob (hb_blob_t *blob)
|
|
|
|
|
{
|
|
|
|
|
bool sane;
|
|
|
|
|
|
|
|
|
|
init (blob);
|
|
|
|
|
|
|
|
|
|
retry:
|
|
|
|
|
DEBUG_MSG_FUNC (SANITIZE, start, "start");
|
|
|
|
|
|
|
|
|
|
start_processing ();
|
|
|
|
|
|
|
|
|
|
if (unlikely (!start))
|
|
|
|
|
{
|
|
|
|
|
end_processing ();
|
|
|
|
|
return blob;
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
Type *t = reinterpret_cast<Type *> (const_cast<char *> (start));
|
|
|
|
|
|
|
|
|
|
sane = t->sanitize (this);
|
|
|
|
|
if (sane)
|
|
|
|
|
{
|
|
|
|
|
if (edit_count)
|
|
|
|
|
{
|
|
|
|
|
DEBUG_MSG_FUNC (SANITIZE, start, "passed first round with %d edits; going for second round", edit_count);
|
|
|
|
|
|
2019-08-24 15:27:14 +02:00
|
|
|
/* sanitize again to ensure no toe-stepping */
|
|
|
|
|
edit_count = 0;
|
2019-03-30 22:59:40 +01:00
|
|
|
sane = t->sanitize (this);
|
|
|
|
|
if (edit_count) {
|
|
|
|
|
DEBUG_MSG_FUNC (SANITIZE, start, "requested %d edits in second round; FAILLING", edit_count);
|
|
|
|
|
sane = false;
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
else
|
|
|
|
|
{
|
|
|
|
|
if (edit_count && !writable) {
|
2019-08-24 15:27:14 +02:00
|
|
|
start = hb_blob_get_data_writable (blob, nullptr);
|
2019-03-30 22:59:40 +01:00
|
|
|
end = start + blob->length;
|
|
|
|
|
|
|
|
|
|
if (start)
|
|
|
|
|
{
|
|
|
|
|
writable = true;
|
|
|
|
|
/* ok, we made it writable by relocating. try again */
|
|
|
|
|
DEBUG_MSG_FUNC (SANITIZE, start, "retry");
|
|
|
|
|
goto retry;
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
end_processing ();
|
|
|
|
|
|
|
|
|
|
DEBUG_MSG_FUNC (SANITIZE, start, sane ? "PASSED" : "FAILED");
|
|
|
|
|
if (sane)
|
|
|
|
|
{
|
|
|
|
|
hb_blob_make_immutable (blob);
|
|
|
|
|
return blob;
|
|
|
|
|
}
|
|
|
|
|
else
|
|
|
|
|
{
|
|
|
|
|
hb_blob_destroy (blob);
|
|
|
|
|
return hb_blob_get_empty ();
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
template <typename Type>
|
|
|
|
|
hb_blob_t *reference_table (const hb_face_t *face, hb_tag_t tableTag = Type::tableTag)
|
|
|
|
|
{
|
|
|
|
|
if (!num_glyphs_set)
|
|
|
|
|
set_num_glyphs (hb_face_get_glyph_count (face));
|
|
|
|
|
return sanitize_blob<Type> (hb_face_reference_table (face, tableTag));
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
const char *start, *end;
|
2020-03-02 20:11:08 +01:00
|
|
|
mutable int max_ops, max_subtables;
|
2019-03-30 22:59:40 +01:00
|
|
|
private:
|
|
|
|
|
bool writable;
|
|
|
|
|
unsigned int edit_count;
|
|
|
|
|
hb_blob_t *blob;
|
|
|
|
|
unsigned int num_glyphs;
|
|
|
|
|
bool num_glyphs_set;
|
|
|
|
|
};
|
|
|
|
|
|
|
|
|
|
struct hb_sanitize_with_object_t
|
|
|
|
|
{
|
|
|
|
|
template <typename T>
|
|
|
|
|
hb_sanitize_with_object_t (hb_sanitize_context_t *c, const T& obj) : c (c)
|
|
|
|
|
{ c->set_object (obj); }
|
|
|
|
|
~hb_sanitize_with_object_t ()
|
|
|
|
|
{ c->reset_object (); }
|
|
|
|
|
|
|
|
|
|
private:
|
|
|
|
|
hb_sanitize_context_t *c;
|
|
|
|
|
};
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
#endif /* HB_SANITIZE_HH */
|
