<format>: Detect some invalid contiguous ranges in range_formatter
#5187
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CaseyCarter
suggested changes
Dec 12, 2024
tests/std/tests/P2286R8_text_formatting_range_string_death/test.cpp
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I haven't thought about this too deeply, but I'd recommend any pathological checks be controlled by |
CaseyCarter
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Dec 17, 2024
StephanTLavavej
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Jan 7, 2025
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I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed. |
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Thanks for fixing this obscure bug! 🛠️ 🐞 🪄 |
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The following code snippet detects some "impossible" huge range.
STL/stl/inc/format
Lines 3283 to 3290 in 89ca073
The semantic requirements of
contiguous_iteratordepend on pointer arithmetic, so when the underlyingcontiguous_rangehas more than 1 elements, the range must denote a contiguous element sequence of some array to be valid (otherwise, reaching from the beginning to the end causes UB). Moreover, the C++ object model doesn't permit an array object to have more thanSIZE_MAXelement. So we can infer that when the size of the contiguous range is too large to fit intosize_t, the range must be invalid, and thus formatting it results in UB (per [iterator.requirements.general]/10, although the paragraph seemingly accidently makes infinite range invalid).Fixes #5182.