Susctl CVE-2024-54507: A particularly 'sus' sysctl in the XNU kernel

Re:Susctl CVE-2024-54507: A particularly 'sus' sysctl in the... by kccqzy on Thursday January 23, 2025 @09:03PM (#42809897)

Well there's the so-called usual arithmetic conversions that will basically convert every uint16_t to an unsigned int. The C and C++ languages do a silent conversion on your back anyways so you might as well make it explicit.

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Re:Susctl CVE-2024-54507: A particularly 'sus' sysctl in the... by loeg on Thursday January 23, 2025 @11:37PM (#42810579)

Usually promotions are to signed int, not unsigned. (With some exceptions. But every uint16_t value can fit in int.)

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Re:Susctl CVE-2024-54507: A particularly 'sus' sysctl in the... by Filligree on Friday January 24, 2025 @07:22AM (#42812428)

Unless int is 16-bit. Code like this is potentially UB; you should use int32_t as the target.

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Re:Susctl CVE-2024-54507: A particularly 'sus' sysctl in the... by kevin_thibedeau on Friday January 24, 2025 @09:16AM (#42813211)

You should use long, and don't ever assume it's exactly 32-bits. The fixed size types are often an overused crutch that hampers future portability.

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Re:Susctl CVE-2024-54507: A particularly 'sus' sysctl in the... by loeg on Friday January 24, 2025 @12:41PM (#42815479)

There are no mainstream 16-bit int platforms. It's fine to know what you target.

The promotions that are really surprising are from uint64_t bitfields to int (because it's based on value representability).

  struct {
    uint64_t a : 33,
             b : 15;
  } s;
  // s.b gets "promoted" to int, s.a does not

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Re:Susctl CVE-2024-54507: A particularly 'sus' sysctl in the... by inetknght on Thursday January 23, 2025 @09:10PM (#42809920)

A well-configured C++ compiler will error-out on such a silent conversion.

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Re:Susctl CVE-2024-54507: A particularly 'sus' sysctl in the... by kccqzy on Thursday January 23, 2025 @09:23PM (#42809969)

The C++ compiler is required to perform this silent conversion according to the standard: https://en.cppreference.com/w/cpp/language/implicit_conversi...

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