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| 1 // Copyright 2016 The Chromium Authors. All rights reserved. |
| 2 // Use of this source code is governed by a BSD-style license that can be |
| 3 // found in the LICENSE file. |
| 4 |
| 5 #include "chromeos/printing/ppd_cache.h" |
| 6 |
| 7 #include <vector> |
| 8 |
| 9 #include "base/files/file_util.h" |
| 10 #include "base/memory/ptr_util.h" |
| 11 #include "base/strings/string_number_conversions.h" |
| 12 #include "base/strings/string_util.h" |
| 13 #include "crypto/sha2.h" |
| 14 #include "net/base/io_buffer.h" |
| 15 #include "net/filter/filter.h" |
| 16 #include "net/filter/gzip_header.h" |
| 17 |
| 18 using base::FilePath; |
| 19 using std::string; |
| 20 |
| 21 namespace chromeos { |
| 22 namespace printing { |
| 23 namespace { |
| 24 |
| 25 // Return true if it looks like contents is already gzipped, false otherwise. |
| 26 bool IsGZipped(const string& contents) { |
| 27 const char* ignored; |
| 28 net::GZipHeader header; |
| 29 return header.ReadMore(contents.data(), contents.size(), &ignored) == |
| 30 net::GZipHeader::COMPLETE_HEADER; |
| 31 } |
| 32 |
| 33 class PpdCacheImpl : public PpdCache { |
| 34 public: |
| 35 explicit PpdCacheImpl(const FilePath& cache_base_dir) |
| 36 : cache_base_dir_(cache_base_dir) {} |
| 37 ~PpdCacheImpl() override {} |
| 38 |
| 39 // Public API functions. |
| 40 base::Optional<FilePath> Find( |
| 41 const Printer::PpdReference& reference) const override { |
| 42 base::Optional<FilePath> ret; |
| 43 |
| 44 // We can't know here if we have a gzipped or un-gzipped version, so just |
| 45 // look for both. |
| 46 FilePath contents_path_base = GetCachePathBase(reference); |
| 47 for (const string& extension : {".ppd", ".ppd.gz"}) { |
| 48 FilePath contents_path = contents_path_base.AddExtension(extension); |
| 49 if (base::PathExists(contents_path)) { |
| 50 ret = contents_path; |
| 51 break; |
| 52 } |
| 53 } |
| 54 return ret; |
| 55 } |
| 56 |
| 57 base::Optional<FilePath> Store(const Printer::PpdReference& reference, |
| 58 const string& ppd_contents) override { |
| 59 base::Optional<FilePath> ret; |
| 60 FilePath contents_path = GetCachePathBase(reference).AddExtension(".ppd"); |
| 61 if (IsGZipped(ppd_contents)) { |
| 62 contents_path = contents_path.AddExtension(".gz"); |
| 63 } |
| 64 if (base::WriteFile(contents_path, ppd_contents.data(), |
| 65 ppd_contents.size()) == |
| 66 static_cast<int>(ppd_contents.size())) { |
| 67 ret = contents_path; |
| 68 } else { |
| 69 LOG(ERROR) << "Failed to write " << contents_path.LossyDisplayName(); |
| 70 // Try to clean up the file, as it may have partial contents. Note that |
| 71 // DeleteFile(nonexistant file) should return true, so failure here means |
| 72 // something is exceptionally hosed. |
| 73 if (!base::DeleteFile(contents_path, false)) { |
| 74 LOG(ERROR) << "Failed to cleanup partially-written file " |
| 75 << contents_path.LossyDisplayName(); |
| 76 return ret; |
| 77 } |
| 78 } |
| 79 return ret; |
| 80 } |
| 81 |
| 82 private: |
| 83 // Get the file path at which we expect to find a PPD if it's cached. |
| 84 // |
| 85 // This is, ultimately, just a hash function. It's extremely infrequently |
| 86 // used (called once when trying to look up information on a printer or store |
| 87 // a PPD), and should be stable, as changing the function will make previously |
| 88 // cached entries unfindable, causing resolve logic to be reinvoked |
| 89 // unnecessarily. |
| 90 // |
| 91 // There's also a faint possibility that a bad actor might try to do something |
| 92 // nefarious by intentionally causing a cache collision that makes the wrong |
| 93 // PPD be used for a printer. There's no obvious attack vector, but |
| 94 // there's also no real cost to being paranoid here, so we use SHA-256 as the |
| 95 // underlying hash function, and inject fixed field prefixes to prevent |
| 96 // field-substitution spoofing. This also buys us hash function stability at |
| 97 // the same time. |
| 98 // |
| 99 // Also, care should be taken to preserve the existing hash values if new |
| 100 // fields are added to PpdReference -- that is, if a new field F is added |
| 101 // to PpdReference, a PpdReference with a default F value should hash to |
| 102 // the same thing as a PpdReference that predates the addition of F to the |
| 103 // structure. |
| 104 // |
| 105 // Note this function expects that the caller will append ".ppd", or ".ppd.gz" |
| 106 // to the output as needed. |
| 107 FilePath GetCachePathBase(const Printer::PpdReference& ref) const { |
| 108 std::vector<string> pieces; |
| 109 if (!ref.user_supplied_ppd_url.empty()) { |
| 110 pieces.push_back("user_supplied_ppd_url:"); |
| 111 pieces.push_back(ref.user_supplied_ppd_url); |
| 112 } else if (!ref.effective_manufacturer.empty() && |
| 113 !ref.effective_model.empty()) { |
| 114 pieces.push_back("manufacturer:"); |
| 115 pieces.push_back(ref.effective_manufacturer); |
| 116 pieces.push_back("model:"); |
| 117 pieces.push_back(ref.effective_model); |
| 118 } else { |
| 119 NOTREACHED() << "PpdCache hashing empty PpdReference"; |
| 120 } |
| 121 // The separator here is not needed, but makes debug output more readable. |
| 122 string full_key = base::JoinString(pieces, "|"); |
| 123 string hashed_key = crypto::SHA256HashString(full_key); |
| 124 string ascii_hash = base::HexEncode(hashed_key.data(), hashed_key.size()); |
| 125 VLOG(3) << "PPD Cache key is " << full_key << " which hashes to " |
| 126 << ascii_hash; |
| 127 |
| 128 return cache_base_dir_.Append(ascii_hash); |
| 129 } |
| 130 |
| 131 const FilePath cache_base_dir_; |
| 132 |
| 133 DISALLOW_COPY_AND_ASSIGN(PpdCacheImpl); |
| 134 }; |
| 135 |
| 136 } // namespace |
| 137 |
| 138 // static |
| 139 std::unique_ptr<PpdCache> PpdCache::Create(const FilePath& cache_base_dir) { |
| 140 return base::MakeUnique<PpdCacheImpl>(cache_base_dir); |
| 141 } |
| 142 |
| 143 } // namespace printing |
| 144 } // namespace chromeos |
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