Fix the xattr read loop bounds (#658)

Fixes the `xattr` read loop bounds. Resolves the failing added tests:

> ✘ Test lastXattrNotDroppedAtBufferBoundary() recorded an issue at
TestEXT4ExtendedAttributes.swift:72:13: Expectation failed: (attrs.count
→ 0) == 1
> ✘ Test lastXattrNotDroppedAtBufferBoundary() failed after 0.001
seconds with 1 issue.

> Swift/Array.swift:430: Fatal error: Array index is out of range

Author: dkovba

Sources/ContainerizationEXT4/EXT4+Xattrs.swift

@@ -257,13 +257,13 @@ extension EXT4 {
             var i = start
             var attribs: [ExtendedAttribute] = []
             // 16 is the size of 1 XAttrEntry
-            while i + 16 < buffer.count {
+            while i + 16 <= buffer.count {
                 let attributeStart = i
                 let rawXattrEntry = Array(buffer[i..<i + 16])
                 let xattrEntry = try EXT4.XAttrEntry(using: rawXattrEntry)
                 i += 16
                 var endIndex = i + Int(xattrEntry.nameLength)
-                guard endIndex < buffer.count else {
+                guard endIndex <= buffer.count else {
                     continue
                 }
                 let rawName = buffer[i..<endIndex]
@@ -272,6 +272,9 @@ extension EXT4 {
                 }
                 let valueStart = Int(xattrEntry.valueOffset) + offset
                 let valueEnd = Int(xattrEntry.valueOffset) + Int(xattrEntry.valueSize) + offset
+                guard valueEnd <= buffer.count else {
+                    break
+                }
                 let value = [UInt8](buffer[valueStart..<valueEnd])
                 let xattr = ExtendedAttribute(idx: xattrEntry.nameIndex, compressedName: name, value: value)
                 attribs.append(xattr)

Tests/ContainerizationEXT4Tests/TestEXT4ExtendedAttributes.swift

@@ -51,6 +51,34 @@ struct TestEXT4ExtendedAttribute {
         }
     }
 
+    @Test func lastXattrNotDroppedAtBufferBoundary() throws {
+        let buffer: [UInt8] = [
+            0,  // nameLength
+            8,  // nameIndex
+            0, 0,  // valueOffset
+            0, 0, 0, 0,  // valueInum
+            0, 0, 0, 0,  // valueSize
+            0, 0, 0, 0,  // hash
+        ]
+        let attrs = try EXT4.FileXattrsState.read(buffer: buffer, start: 0, offset: 0)
+        try #require(attrs.count == 1)
+        #expect(attrs[0].fullName == "system.richacl")
+    }
+
+    @Test func xattrOutOfBoundsValueDoesNotCrash() throws {
+        let buffer: [UInt8] = [
+            1,  // nameLength
+            1,  // nameIndex
+            17, 0,  // valueOffset
+            0, 0, 0, 0,  // valueInum
+            4, 0, 0, 0,  // valueSize
+            0, 0, 0, 0,  // hash
+            UInt8(ascii: "a"), 0, 0, 0,  // name
+        ]
+        let attrs = try EXT4.FileXattrsState.read(buffer: buffer, start: 0, offset: 0)
+        #expect(attrs.isEmpty)
+    }
+
     @Test func encodeDecodeAttributes() {
         let xattrs: [String: Data] = [
             "foo.bar": Data([1, 2, 3]),