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Fix the xattr read loop bounds #658

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Fix the xattr read loop bounds #658

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aeafb93
Add a test for the last `xattr` dropped at the buffer boundary
dkovba Apr 7, 2026
89cf6f0
Fix for the last `xattr` dropped at the buffer boundary
dkovba Apr 7, 2026
b5384dd
Add a test for the out-of-bounds `xattr` value crash
dkovba Apr 7, 2026
04d4efe
Fix for the out-of-bounds `xattr` value crash
dkovba Apr 7, 2026
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7 changes: 5 additions & 2 deletions Sources/ContainerizationEXT4/EXT4+Xattrs.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -257,19 +257,22 @@ 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]
let name = String(bytes: rawName, encoding: .ascii)!
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)
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28 changes: 28 additions & 0 deletions Tests/ContainerizationEXT4Tests/TestEXT4ExtendedAttributes.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -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]),
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