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lib/mergeset: misuse of unsafe.Pointer

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It appears the `lib/mergeset.Item` violates the 3rd rule
https://pkg.go.dev/unsafe#Pointer

> (3) Conversion of a Pointer to a uintptr and back, with arithmetic.
> 
> Unlike in C, it is not valid to advance a pointer just beyond the end
of its original allocation:
> ```
> // INVALID: end points outside allocated space.
> b := make([]byte, n)`
> end = unsafe.Pointer(uintptr(unsafe.Pointer(&b[0])) + uintptr(n))
> ```


`CGO_ENABLED=0 go test -trimpath -gcflags=all=-d=checkptr -run
TestTableAddItemsSerial`
```
fatal error: checkptr: pointer arithmetic result points to invalid allocation


 This commit adds a special path to item encoding, that prevents invalid memory references.

 See this PR for details:
https://github.com/VictoriaMetrics/VictoriaMetrics/pull/9264
This commit is contained in:
Alexander Frolov
2025-06-30 16:56:28 +02:00
committed by GitHub
parent 21878f0760
commit f9aa74c367
1 changed files with 10 additions and 4 deletions
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14
lib/mergeset/encoding.go
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@@ -28,16 +28,22 @@ type Item struct {
//
// The returned bytes representation belongs to data.
func (it Item) Bytes(data []byte) []byte {
n := int(it.End - it.Start)
return unsafe.Slice((*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(unsafe.SliceData(data)))+uintptr(it.Start))), n)
n := it.End - it.Start
if n == 0 {
return nil
}
return unsafe.Slice((*byte)(unsafe.Add(unsafe.Pointer(unsafe.SliceData(data)), it.Start)), n)
}
// String returns string representation of it obtained from data.
//
// The returned string representation belongs to data.
func (it Item) String(data []byte) string {
n := int(it.End - it.Start)
return unsafe.String((*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(unsafe.SliceData(data)))+uintptr(it.Start))), n)
n := it.End - it.Start
if n == 0 {
return ""
}
return unsafe.String((*byte)(unsafe.Add(unsafe.Pointer(unsafe.SliceData(data)), it.Start)), n)
}
func (ib *inmemoryBlock) Len() int {