Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH 00/13] [RFC] Rust support | Date | Thu, 15 Apr 2021 08:26:21 +0000 |
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... > Besides just FP, 128-bit, etc, I remain concerned about just basic > math operations. C has no way to describe the intent of integer > overflow, so the kernel was left with the only "predictable" result: > wrap around. Unfortunately, this is wrong in most cases, and we're left > with entire classes of vulnerability related to such overflows.
I'm not sure any of the alternatives (except perhaps panic) are much better. Many years ago I used a COBOL system that skipped the assignment if ADD X to Y (y += x) would overflow. That gave a very hard to spot error when the sump of a long list way a little too large. If it had wrapped the error would be obvious.
There are certainly places where saturate is good. Mostly when dealing with analogue samples.
I guess the problematic code is stuff that checks: if (foo->size + constant > limit) goto error; instead of: if (foo->size > limit - constant) goto error;
David
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