fix: stack-buffer-overflow (#1550), wrong statvfs block_size (#1547), path traversal (#1516)

[Hardikrepo]

Summary

This PR fixes three bugs found in the dev branch:

Fix #1550 — Stack-buffer-overflow in UtAssert_StringBufCompare()

File: ut_assert/src/utassert.c

Root cause: ScrubbedString1[256] and ScrubbedString2[256] are fixed 256-byte stack buffers. When a fixed-length buffer longer than 255 bytes contains no NUL within the requested bound, FormatLen1/FormatLen2 are set directly from the caller-supplied String1Max/String2Max. The subsequent memcpy writes past the end of the stack buffers causing a stack-buffer-overflow.

Fix: Clamp FormatLen1 and FormatLen2 to sizeof(ScrubbedString) - 1 (255) immediately before any memcpy, ensuring the copy never exceeds the buffer boundary.

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Fix #1547 — OS_FileSysStatVolume_Impl() uses wrong statvfs field for block size

Files: src/os/posix/src/os-impl-filesys.c, src/os/qnx/src/os-impl-filesys.c, src/os/rtems/src/os-impl-filesys.c

Root cause: After migrating to statvfs(), the POSIX, QNX, and RTEMS implementations still assign stat_buf.f_bsize to result->block_size. Per POSIX, f_bsize is the preferred I/O transfer block size while f_frsize is the fundamental file system block size used to compute actual storage (i.e. total_blocks * f_frsize = total bytes). On large drives these values are not guaranteed to be equal, causing incorrect free/total byte calculations.

Fix: Replace stat_buf.f_bsize with stat_buf.f_frsize in all three affected OS ports.

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Fix #1516 — Path traversal via unchecked .. components in OS_FileSys_FindVirtMountPoint()

File: src/os/shared/src/osapi-filesys.c

Root cause: OS_FileSys_FindVirtMountPoint() performed only a prefix match against the virtual mount point. A path such as /mnt/abc/../secret would match the /mnt/abc mount point because the prefix check passes and target[mplen] == '/'. An attacker could craft a path that traverses outside the virtual mount boundary.

Fix: Before performing the prefix match, scan the target path for any /../ or trailing /.. sequence and return false immediately if found. Also rejects paths starting with ../.

Files Changed

File	Issue	Change
ut_assert/src/utassert.c	#1550	Clamp FormatLen before memcpy
src/os/posix/src/os-impl-filesys.c	#1547	f_bsize → f_frsize
src/os/qnx/src/os-impl-filesys.c	#1547	f_bsize → f_frsize
src/os/rtems/src/os-impl-filesys.c	#1547	f_bsize → f_frsize
src/os/shared/src/osapi-filesys.c	#1516	Reject paths with .. components

Test plan

• UtAssert_STRINGBUF_EQ() with buffers longer than 255 bytes no longer causes stack-buffer-overflow
• OS_FileSysStatVolume() returns correct byte counts on large drives where f_frsize != f_bsize
• OS_FileSys_FindVirtMountPoint() returns false for paths containing /../ or .. traversal
• Existing unit tests pass with no regressions