[all-commits] [llvm/llvm-project] bde4ff: Don't pass null pointers to memcmp and memcpy in l...

[David Benjamin via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: bde4ffe7521421cfa891c7d6e526566920326b3f
      https://github.com/llvm/llvm-project/commit/bde4ffe7521421cfa891c7d6e526566920326b3f
  Author: David Benjamin <davidben at google.com>
  Date:   2024-08-13 (Tue, 13 Aug 2024)

  Changed paths:
    M compiler-rt/lib/fuzzer/FuzzerDictionary.h
    M compiler-rt/lib/fuzzer/FuzzerLoop.cpp

  Log Message:
  -----------
  Don't pass null pointers to memcmp and memcpy in libFuzzer (#96775)

In C, it is UB to call `memcmp(NULL, NULL, 0)`, `memcpy(NULL, NULL, 0)`,
etc. Unfortunately, `(NULL, 0)` is the natural representation of an
empty sequence of objects and extremely common in real world code. As a
result, all C code, and C++ code which calls into C functions, must
carefully guard all calls to `memcpy`.

This is a serious, real world usability issue in C and should be fixed
in the language (see #49459). In the meantime, pay the cost of the extra
branch to avoid tripping UBSan in libFuzzer. Once the usability problem
in C has been fixed, these checks can be removed.

Fixes #96772



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