Fix memory safety vulnerabilities in high-level and VFD code

[brtnfld]

Address multiple CWE-415 (double-free), CWE-416 (use-after-free), and CWE-122 (buffer overflow) vulnerabilities identified by static analysis:

• hl/src/H5DS.c: Fix double-free in H5DSis_scale() by setting buf to NULL after free and adding NULL check in cleanup path

• hl/src/H5LT.c: Fix multiple memory issues:

  • Set myinput to NULL after free in H5LTtext_to_dtype()
  • Add NULL check in realloc_and_append() to prevent use-after-free
  • Refactor duplicated stmp handling by creating H5LT_append_dtype_super_text() helper function, eliminating ~50 lines of repeated code across 4 case blocks

• hl/src/H5TB.c: Replace unsafe strcpy() with strncpy() in H5TBget_field_info() using HLTB_MAX_FIELD_LEN constant to prevent buffer overflow

• hl/src/H5TBpublic.h: Document buffer size requirements for field_names parameter

• src/H5FDstdio.c: Fix inconsistent resource cleanup in H5FD_stdio_open() by using file->fp instead of f throughout error paths

• src/H5VLnative.c: Add assert checks for obj and file parameters in H5VL_native_get_file_struct() following internal API conventions

SAFE project work.

---

Important

Fixes memory safety vulnerabilities in HDF5 codebase, addressing double-free, use-after-free, and buffer overflow issues across multiple files.

• Memory Safety Fixes:
  • H5DS.c: Fix double-free in H5DSis_scale() by setting buf to NULL after free and adding NULL check in cleanup.
  • H5LT.c: Set myinput to NULL after free in H5LTtext_to_dtype(), add NULL check in realloc_and_append(), refactor H5LT_append_dtype_super_text() to reduce code duplication.
  • H5TB.c: Replace strcpy() with strncpy() in H5TBget_field_info() to prevent buffer overflow.
• Documentation:
  • H5TBpublic.h: Document buffer size requirements for field_names parameter.
• Resource Management:
  • H5FDstdio.c: Use file->fp consistently in H5FD_stdio_open() for error paths.
• Assertions:
  • H5VLnative.c: Add assert checks for obj and file parameters in H5VL_native_get_file_struct().

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[jhendersonHDF]

What was the issue with these close calls? file->fp should be the same as f at this point

[brtnfld]

Snyk flags it for clarity on resource ownership. The concern is that it's not explicit which pointer "owns" the resource after the assignment. Once you've assigned file->fp = f, the FILE* is conceptually owned by the file structure, and using file->fp in cleanup makes this ownership clear.

[jhendersonHDF]

The intent of the _no_user_buf parameter isn't really obvious, but it seems like this check overlaps with the same check inside that block, which seems like it would imply buf being allowed to be passed in as NULL in the false case. But I'm guessing this check was added due to the strlen(buf) below. This seems like we should determine whether it was ever intended for buf to be allowed as NULL.

[jhendersonHDF]

Harmless, but it's probably unnecessary to document that a macro used to be in this file