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Fix size calculations in the WinFSP symlink reparse buffer #233

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Fix size calculations in the WinFSP symlink reparse buffer #233

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12 changes: 7 additions & 5 deletions pkg/filesystem/virtual/winfsp/file_system.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1291,10 +1291,11 @@ func FillSymlinkReparseBuffer(target string, flags uint32, buffer []byte) (int,
// utf-16 encoded so 2 bytes per character; no null terminator needed.
targetUTF16Len := len(targetUTF16) - 1
targetUTF16Bytes := targetUTF16Len * 2
symbolicLinkReparseSize := int(unsafe.Sizeof(windowsext.SymbolicLinkReparseBuffer{})) -
// Exclude the PathBuffer member.
2 +
// Two copies of the target path.
// The buffer holds two copies of the target (SubstituteName + PrintName).
// Header size is PathBuffer's offset. Don't compute it as sizeof minus the
// placeholder element — sizeof rounds up for the uint32 Flags field, so that
// leaves 2 bytes of trailing padding and over-counts ReparseDataLength.
symbolicLinkReparseSize := int(unsafe.Offsetof(windowsext.SymbolicLinkReparseBuffer{}.PathBuffer)) +
targetUTF16Bytes*2
requiredSize := int(unsafe.Sizeof(windowsext.REPARSE_DATA_BUFFER_HEADER{})) + symbolicLinkReparseSize
if len(buffer) < requiredSize {
Expand All @@ -1313,7 +1314,8 @@ func FillSymlinkReparseBuffer(target string, flags uint32, buffer []byte) (int,
slrb.PrintNameOffset = uint16(targetUTF16Bytes)
slrb.PrintNameLength = uint16(targetUTF16Bytes)

pathBuffer := unsafe.Slice(&slrb.PathBuffer[0], 2*targetUTF16Bytes)
// unsafe.Slice's length is in uint16 elements, not bytes.
pathBuffer := unsafe.Slice(&slrb.PathBuffer[0], 2*targetUTF16Len)
copy(pathBuffer[0:targetUTF16Len], targetUTF16)
copy(pathBuffer[targetUTF16Len:targetUTF16Len*2], targetUTF16)

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