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LibRegex: Add bounds check to Lexer::back()

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If the offset is zero and we're already at the end of the lexer's input
an out of bounds read (m_source[m_position]) would occur.
Also check that the offset is not more than m_position (which should
never be the case, and would result in m_position underflowing).

Fixes #4253.
This commit is contained in:
Linus Groh 2020-11-29 23:32:29 +00:00 • committed by Andreas Kling
parent 7094697743
commit 8284f87867
1 changed files with 4 additions and 1 deletions
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5
Libraries/LibRegex/RegexLexer.cpp
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@ -64,8 +64,11 @@ ALWAYS_INLINE char Lexer::peek(size_t offset) const
void Lexer::back(size_t offset) void Lexer::back(size_t offset)
{ {
ASSERT(offset <= m_position);
if (!offset)
return;
m_position -= offset; m_position -= offset;
m_previous_position = m_position - 1; m_previous_position = (m_position > 0) ? m_position - 1 : 0;
m_current_char = m_source[m_position]; m_current_char = m_source[m_position];
} }