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Merge #19508: Work around memory-aliasing in descriptor ParsePubkey

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fa2ae0ac8d span: Add Span::empty() and use it in script/descriptor (MarcoFalke)
fa8a992589 Work around memory-aliasing in descriptor ParsePubkey (MarcoFalke)

Pull request description:

  While this is not undefined behaviour, the memory aliasing trick is confusing when reading the code. Having `a.size()==0` and then access `a[0]` works in this particular case, but should probably be avoided to harden the code for the future.

ACKs for top commit:
  theStack:
    re-ACK fa2ae0ac8d
  elichai:
    ACK fa2ae0ac8d
  jonatack:
    ACK fa2ae0ac8d

Tree-SHA512: 0ec7b09eef45504973a195923cdf1aa8522117c8e2f69b453e5ce9aa8a7e327c71138518022c32d05133dc99cb861101ed0f60fa891814ee3e9dab3a6fa61a84
This commit is contained in:
MarcoFalke 2020-07-26 19:01:48 +02:00
commit 31d2b4098a
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2 changed files with 5 additions and 3 deletions
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7
src/script/descriptor.cpp
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@ -825,8 +825,9 @@ std::unique_ptr<PubkeyProvider> ParsePubkey(uint32_t key_exp_index, const Span<c
return nullptr; return nullptr;
} }
if (origin_split.size() == 1) return ParsePubkeyInner(key_exp_index, origin_split[0], permit_uncompressed, out, error); if (origin_split.size() == 1) return ParsePubkeyInner(key_exp_index, origin_split[0], permit_uncompressed, out, error);
if (origin_split[0].size() < 1 || origin_split[0][0] != '[') { if (origin_split[0].empty() || origin_split[0][0] != '[') {
error = strprintf("Key origin start '[ character expected but not found, got '%c' instead", origin_split[0][0]); error = strprintf("Key origin start '[ character expected but not found, got '%c' instead",
origin_split[0].empty() ? /** empty, implies split char */ ']' : origin_split[0][0]);
return nullptr; return nullptr;
} }
auto slash_split = Split(origin_split[0].subspan(1), '/'); auto slash_split = Split(origin_split[0].subspan(1), '/');
@ -896,7 +897,7 @@ std::unique_ptr<DescriptorImpl> ParseScript(uint32_t key_exp_index, Span<const c
providers.emplace_back(std::move(pk)); providers.emplace_back(std::move(pk));
key_exp_index++; key_exp_index++;
} }
if (providers.size() < 1 || providers.size() > 16) { if (providers.empty() || providers.size() > 16) {
error = strprintf("Cannot have %u keys in multisig; must have between 1 and 16 keys, inclusive", providers.size()); error = strprintf("Cannot have %u keys in multisig; must have between 1 and 16 keys, inclusive", providers.size());
return nullptr; return nullptr;
} else if (thres < 1) { } else if (thres < 1) {

1
src/span.h
View file

@ -151,6 +151,7 @@ public:
return m_data[m_size - 1]; return m_data[m_size - 1];
} }
constexpr std::size_t size() const noexcept { return m_size; } constexpr std::size_t size() const noexcept { return m_size; }
constexpr bool empty() const noexcept { return size() == 0; }
CONSTEXPR_IF_NOT_DEBUG C& operator[](std::size_t pos) const noexcept CONSTEXPR_IF_NOT_DEBUG C& operator[](std::size_t pos) const noexcept
{ {
ASSERT_IF_DEBUG(size() > pos); ASSERT_IF_DEBUG(size() > pos);