3038. polymorphic_allocator::allocate should not allow integer overflow to create vulnerabilities

Section: [mem.poly.allocator.mem] Status: New Submitter: Billy O'Neal III Opened: 2017-11-16 Last modified: 2017-11-25

Priority: 2

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At the moment polymorphic_allocator is specified to do sizeof(T) * n directly; this may allow an attacker to cause this calculation to overflow, resulting in allocate() not meeting its postcondition of returning a buffer suitable to store n copies of T; this is a common bug described in CWE-190.

Making this into a saturating multiply should be sufficient to avoid this problem; any memory_resource underneath polymorphic_allocator is going to have to throw bad_alloc (or another exception) for a request of SIZE_MAX.

(There's also a minor editorial thing here that Returns should be Effects)

Proposed resolution:

Wording relative to N4700.

  1. Edit [mem.poly.allocator.mem] as indicated:

    Tp* allocate(size_t n);

    -1- ReturnsEffects: Equivalent to

    return static_cast<Tp*>(memory_rsrc->allocate(SIZE_MAX / sizeof(Tp) < n ? SIZE_MAX : n * sizeof(Tp), alignof(Tp)));