refactor(elf): centralize raw table declarations

src/application/MipsElfMetadata.ts

@@ -1,3 +1,4 @@
+import { readElfRawTableDeclarations } from "../domain/elfRawTableDeclarations.js";
 import type { FileHandle } from "node:fs/promises";
 import type {
   MipsAbiFlags,
@@ -91,12 +92,15 @@ export const readMipsElfMetadata = async (
   if (fixedHeader.value.headerSize !== 52)
     return err("invalid MIPS ELF32 version or header size");
 
+  const raw = readElfRawTableDeclarations(bytes, fixedHeader.value);
+  if (!raw.ok) return err(raw.error.message);
+  const { programs, sections } = raw.value;
   const tables = [
     {
       label: "program header table",
-      offset: u32(bytes, 28),
-      count: u16(bytes, 44),
-      stride: u16(bytes, 42),
+      offset: Number(programs.offset),
+      count: programs.count,
+      stride: programs.width,
       entrySize: 32,
       typeOffset: 0,
       dataOffset: 4,
@@ -106,9 +110,9 @@ export const readMipsElfMetadata = async (
     },
     {
       label: "section header table",
-      offset: u32(bytes, 32),
-      count: u16(bytes, 48),
-      stride: u16(bytes, 46),
+      offset: Number(sections.offset),
+      count: sections.count,
+      stride: sections.width,
       entrySize: 40,
       typeOffset: 4,
       dataOffset: 16,
@@ -119,7 +123,7 @@ export const readMipsElfMetadata = async (
   ];
   // Extended numbering needs a separate section-zero reader. Refuse it rather
   // than silently treating an unexamined table as having no ABI declarations.
-  if (u16(bytes, 44) === 0xffff || u16(bytes, 48) >= 0xff00)
+  if (programs.count === 0xffff || sections.count >= 0xff00)
     return err("extended or reserved MIPS ELF table numbering is unsupported");
   let record: Buffer | undefined;
   let sharedLoad: MipsElfMetadata["sharedLoad"];

src/artifacts/nodeSea/NodeSeaLocation.ts

@@ -1,3 +1,4 @@
+import { readElfRawTableDeclarations } from "../../domain/elfRawTableDeclarations.js";
 import { createHash } from "node:crypto";
 import { parsePeResources } from "../../native/pe/PeResourceParser.js";
 import {
@@ -323,16 +324,22 @@ const locateElfNotes = async (
     Math.min(carrier.fileSize, header.value.headerSize),
   );
   if (fields === undefined) return [];
-  const phoff = elf64
-    ? readU64(fields, 32, little)
-    : readU32(fields, 28, little);
-  const shoff = elf64
-    ? readU64(fields, 40, little)
-    : readU32(fields, 32, little);
-  const phentsize = readU16(fields, elf64 ? 54 : 42, little);
-  const phnum = readU16(fields, elf64 ? 56 : 44, little);
-  const shentsize = readU16(fields, elf64 ? 58 : 46, little);
-  const shnum = readU16(fields, elf64 ? 60 : 48, little);
+  const raw = readElfRawTableDeclarations(fields, header.value);
+  if (!raw.ok) return [];
+  const { programs: programDeclarations, sections: sectionDeclarations } =
+    raw.value;
+  const phoff =
+    programDeclarations.offset <= BigInt(Number.MAX_SAFE_INTEGER)
+      ? Number(programDeclarations.offset)
+      : undefined;
+  const shoff =
+    sectionDeclarations.offset <= BigInt(Number.MAX_SAFE_INTEGER)
+      ? Number(sectionDeclarations.offset)
+      : undefined;
+  const phentsize = programDeclarations.width;
+  const phnum = programDeclarations.count;
+  const shentsize = sectionDeclarations.width;
+  const shnum = sectionDeclarations.count;
   const minimumProgram = elf64 ? 56 : 32;
   const minimumSection = elf64 ? 64 : 40;
   const found: BlobRange[] = [];
@@ -645,9 +652,6 @@ const cString = (bytes: Buffer, offset: number, length: number): string => {
   return bytes.toString("latin1", offset, end);
 };
 
-const readU16 = (bytes: Buffer, offset: number, little: boolean): number =>
-  little ? bytes.readUInt16LE(offset) : bytes.readUInt16BE(offset);
-
 const readU32 = (bytes: Buffer, offset: number, little: boolean): number =>
   little ? bytes.readUInt32LE(offset) : bytes.readUInt32BE(offset);
 

src/domain/elfDeclaredRanges.ts

@@ -1,3 +1,4 @@
+import { readElfRawTableDeclarations } from "./elfRawTableDeclarations.js";
 import { readElfFixedHeader, type ElfFixedHeader } from "./elfFixedHeader.js";
 import { err, ok, type Result } from "./result.js";
 
@@ -21,8 +22,6 @@ export interface ElfTableDeclarations {
 
 const reader = (bytes: Buffer, header: ElfFixedHeader) => {
   const little = header.byteOrder === "little";
-  const u16 = (at: number) =>
-    little ? bytes.readUInt16LE(at) : bytes.readUInt16BE(at);
   const u32 = (at: number) =>
     little ? bytes.readUInt32LE(at) : bytes.readUInt32BE(at);
   const word = (at: number) =>
@@ -31,7 +30,7 @@ const reader = (bytes: Buffer, header: ElfFixedHeader) => {
       : little
         ? bytes.readBigUInt64LE(at)
         : bytes.readBigUInt64BE(at);
-  return { u16, u32, word };
+  return { u32, word };
 };
 
 /** Zero-sized/inactive declarations own no file bytes. Arithmetic stays exact. */
@@ -110,29 +109,6 @@ const extendedCounts = (
   return ok(counts);
 };
 
-const TABLE_FIELDS = {
-  32: {
-    programOffset: 28,
-    sectionOffset: 32,
-    programWidth: 42,
-    programCount: 44,
-    sectionWidth: 46,
-    sectionCount: 48,
-    namesIndex: 50,
-    sectionHeaderSize: 40,
-  },
-  64: {
-    programOffset: 32,
-    sectionOffset: 40,
-    programWidth: 54,
-    programCount: 56,
-    sectionWidth: 58,
-    sectionCount: 60,
-    namesIndex: 62,
-    sectionHeaderSize: 64,
-  },
-} as const;
-
 /** Canonical table declarations, including extended counts in inactive section zero. */
 export function* readElfTableDeclarations(
   bytes: Buffer,
@@ -141,15 +117,16 @@ export function* readElfTableDeclarations(
   const fixed = readElfFixedHeader(bytes, fileSize);
   if (!fixed.ok) return fixed;
   const header = fixed.value;
-  const r = reader(bytes, header);
-  const fields = TABLE_FIELDS[header.elfClass];
-  const programOffset = r.word(fields.programOffset);
-  const sectionOffset = r.word(fields.sectionOffset);
-  const programWidth = r.u16(fields.programWidth);
-  const sectionWidth = r.u16(fields.sectionWidth);
-  let programCount = BigInt(r.u16(fields.programCount));
-  let sectionCount = BigInt(r.u16(fields.sectionCount));
-  let namesIndex = r.u16(fields.namesIndex);
+  const raw = readElfRawTableDeclarations(bytes, header);
+  if (!raw.ok) return err(raw.error.message);
+  const { programs, sections } = raw.value;
+  const programOffset = programs.offset;
+  const sectionOffset = sections.offset;
+  const programWidth = programs.width;
+  const sectionWidth = sections.width;
+  let programCount = BigInt(programs.count);
+  let sectionCount = BigInt(sections.count);
+  let namesIndex = sections.namesIndex;
   if (
     sectionOffset === 0n &&
     (sectionCount !== 0n || namesIndex !== 0 || programCount === 0xffffn)
@@ -168,7 +145,7 @@ export function* readElfTableDeclarations(
     if (failure !== undefined) return err(failure);
     const first = yield {
       offset: Number(sectionOffset),
-      size: fields.sectionHeaderSize,
+      size: header.elfClass === 64 ? 64 : 40,
     };
     const counts = extendedCounts(first, header, {
       programCount,

src/domain/elfRawTableDeclarations.test.ts

@@ -0,0 +1,68 @@
+import { expect, it } from "vitest";
+import { readElfRawTableDeclarations } from "./elfRawTableDeclarations.js";
+
+const formats = [
+  { elfClass: 32, byteOrder: "little" },
+  { elfClass: 32, byteOrder: "big" },
+  { elfClass: 64, byteOrder: "little" },
+  { elfClass: 64, byteOrder: "big" },
+] as const;
+
+it.each(formats)(
+  "preserves unresolved raw ELF$elfClass $byteOrder declarations",
+  (format) => {
+    const wide = format.elfClass === 64;
+    const little = format.byteOrder === "little";
+    const length = wide ? 64 : 52;
+    const backing = Buffer.alloc(length + 17, 0xa5);
+    const bytes = backing.subarray(7, 7 + length);
+    const view = new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength);
+    const programOffset = wide ? 0xfedcba9876543210n : 0xfedcba98n;
+    const sectionOffset = wide ? 0xffffffffffffffffn : 0xffffffffn;
+    if (wide) {
+      view.setBigUint64(32, programOffset, little);
+      view.setBigUint64(40, sectionOffset, little);
+    } else {
+      view.setUint32(28, Number(programOffset), little);
+      view.setUint32(32, Number(sectionOffset), little);
+    }
+    [1, 0xffff, 2, 0, 0xffff].forEach((value, index) =>
+      view.setUint16((wide ? 54 : 42) + index * 2, value, little),
+    );
+    const before = Buffer.from(backing);
+    const parsed = readElfRawTableDeclarations(backing.subarray(7), format);
+    expect(backing.equals(before)).toBe(true);
+    backing.fill(0);
+    expect(parsed).toEqual({
+      ok: true,
+      value: {
+        programs: { offset: programOffset, width: 1, count: 0xffff },
+        sections: {
+          offset: sectionOffset,
+          width: 2,
+          count: 0,
+          namesIndex: 0xffff,
+        },
+      },
+    });
+    // Format identity and whether these unresolved declarations are admissible belong to callers.
+  },
+);
+
+it.each(formats)(
+  "refuses truncated ELF$elfClass $byteOrder declaration records",
+  (format) => {
+    const length = format.elfClass === 64 ? 64 : 52;
+    const backing = Buffer.alloc(length + 7);
+    for (let observed = 0; observed < length; observed++)
+      expect(
+        readElfRawTableDeclarations(backing.subarray(7, 7 + observed), format),
+      ).toEqual({
+        ok: false,
+        error: {
+          kind: "malformed",
+          message: "ELF table declarations are truncated",
+        },
+      });
+  },
+);

src/domain/elfRawTableDeclarations.ts

@@ -0,0 +1,33 @@
+import { err, ok } from "./result.js";
+
+/** Fixed-header table words, before extended numbering or file-range admission. */
+export const readElfRawTableDeclarations = (
+  bytes: Uint8Array,
+  format: { readonly elfClass: 32 | 64; readonly byteOrder: "little" | "big" },
+) => {
+  const wide = format.elfClass === 64;
+  if (bytes.byteLength < (wide ? 64 : 52))
+    return err({
+      kind: "malformed" as const,
+      message: "ELF table declarations are truncated",
+    });
+  const little = format.byteOrder === "little";
+  const view = new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength);
+  const word = (offset: number): bigint =>
+    wide
+      ? view.getBigUint64(offset, little)
+      : BigInt(view.getUint32(offset, little));
+  return ok({
+    programs: {
+      offset: word(wide ? 32 : 28),
+      width: view.getUint16(wide ? 54 : 42, little),
+      count: view.getUint16(wide ? 56 : 44, little),
+    },
+    sections: {
+      offset: word(wide ? 40 : 32),
+      width: view.getUint16(wide ? 58 : 46, little),
+      count: view.getUint16(wide ? 60 : 48, little),
+      namesIndex: view.getUint16(wide ? 62 : 50, little),
+    },
+  });
+};

src/flutter/DartElf.test.ts

@@ -502,3 +502,22 @@ describe("readSnapshotHeader", () => {
     });
   });
 });
+
+it("keeps section admission ahead of program admission for unrepresentable raw offsets", async () => {
+  const bytes = buildStrippedElf64Image([]);
+  bytes.writeBigUInt64LE(0xffffffffffffffffn, 0x28);
+  bytes.writeBigUInt64LE(0xffffffffffffffffn, 0x20);
+  expect(await readElfSymbols(bytes, ["_kDartVmSnapshotData"])).toEqual({
+    symbols: [],
+    failures: [
+      { reason: "ELF section header table is missing or out of bounds" },
+    ],
+  });
+  bytes.writeBigUInt64LE(0n, 0x28);
+  expect(await readElfSymbols(bytes, ["_kDartVmSnapshotData"])).toEqual({
+    symbols: [],
+    failures: [
+      { reason: "ELF program header table is missing or out of bounds" },
+    ],
+  });
+});

src/flutter/DartElf.ts

@@ -1,3 +1,4 @@
+import { readElfRawTableDeclarations } from "../domain/elfRawTableDeclarations.js";
 import { Buffer } from "node:buffer";
 import { setImmediate as yieldToEventLoop } from "node:timers/promises";
 import { createElfLoadMap } from "./ElfLoadMap.js";
@@ -84,7 +85,6 @@ export const readElfHeader = (
   bytes: Buffer,
   totalBytes: number = bytes.length,
 ) => {
-  const reader = new BoundedReader(bytes);
   const fixedHeader = readElfFixedHeader(bytes, totalBytes);
   if (!fixedHeader.ok) return { failure: { reason: fixedHeader.error } };
   const is64 = fixedHeader.value.elfClass === 64;
@@ -96,21 +96,28 @@ export const readElfHeader = (
   const e_type = fixedHeader.value.type;
   if (e_type !== 1 && e_type !== 2 && e_type !== ET_DYN)
     return { failure: { reason: "unsupported ELF type" } };
-  const e_shoff = is64 ? reader.u64(0x28) : reader.u32(0x20);
-  const e_shentsize = reader.u16(is64 ? 0x3a : 0x2e);
-  const e_shnum = reader.u16(is64 ? 0x3c : 0x30);
-  const e_phoff = is64 ? reader.u64(0x20) : reader.u32(0x1c);
-  const e_phentsize = reader.u16(is64 ? 0x36 : 0x2a);
-  const e_phnum = reader.u16(is64 ? 0x38 : 0x2c);
+  const raw = readElfRawTableDeclarations(bytes, fixedHeader.value);
+  if (!raw.ok) return { failure: { reason: raw.error.message } };
+  const { programs, sections } = raw.value;
+  const e_shoff =
+    sections.offset <= BigInt(Number.MAX_SAFE_INTEGER)
+      ? Number(sections.offset)
+      : null;
+  const e_shentsize = sections.width;
+  const e_shnum = sections.count;
+  const e_phoff =
+    programs.offset <= BigInt(Number.MAX_SAFE_INTEGER)
+      ? Number(programs.offset)
+      : null;
+  const e_phentsize = programs.width;
+  const e_phnum = programs.count;
   const tableFits = (
     offset: number | null,
-    width: number | null,
-    count: number | null,
+    width: number,
+    count: number,
     minimumWidth: number,
   ): boolean =>
     offset !== null &&
-    width !== null &&
-    count !== null &&
     offset >= headerBytes &&
     offset <= totalBytes &&
     width >= minimumWidth &&
@@ -125,8 +132,6 @@ export const readElfHeader = (
     e_type === ET_DYN && e_shoff === 0 && e_shnum === 0;
   if (
     e_shoff === null ||
-    e_shentsize === null ||
-    e_shnum === null ||
     (!sectionTableAbsent &&
       !tableFits(e_shoff, e_shentsize, e_shnum, MIN_SHENT))
   )
@@ -138,8 +143,6 @@ export const readElfHeader = (
   const MIN_PHENT = is64 ? 56 : 32;
   if (
     e_phoff === null ||
-    e_phentsize === null ||
-    e_phnum === null ||
     e_phnum === 0xffff ||
     !tableFits(e_phoff, e_phentsize, e_phnum, MIN_PHENT)
   )

src/native/elf/ElfNoteParser.test.ts

@@ -617,3 +617,11 @@ it("fails when the entry budget is exhausted", () => {
     ),
   ).toThrow(ArtifactReaderFailure);
 });
+
+it("keeps unsafe table offsets ahead of unsupported extended numbering", () => {
+  const bytes = elfExtendedSectionCountFixture();
+  bytes.writeBigUInt64LE(0xffffffffffffffffn, 32);
+  expect(() => parse(bytes)).toThrow(
+    "ELF offset or size exceeds a safe integer.",
+  );
+});

src/native/elf/ElfNoteParser.ts

@@ -1,3 +1,4 @@
+import { readElfRawTableDeclarations } from "../../domain/elfRawTableDeclarations.js";
 import { createHash } from "node:crypto";
 import { ArtifactReaderFailure } from "../../artifacts/ArtifactReader.js";
 import { readElfFixedHeader } from "../../domain/elfFixedHeader.js";
@@ -98,13 +99,6 @@ class ElfReader {
     readonly bits: 32 | 64,
   ) {}
 
-  u16(offset: number): number {
-    this.require(offset, 2);
-    return this.little
-      ? this.bytes.readUInt16LE(offset)
-      : this.bytes.readUInt16BE(offset);
-  }
-
   u32(offset: number): number {
     this.require(offset, 4);
     return this.little
@@ -328,13 +322,21 @@ export const parseElfNotes = (
   );
   const wide = header.elfClass === 64;
   const type = header.type;
-  const phoff = reader.word(wide ? 32 : 28);
-  const shoff = reader.word(wide ? 40 : 32);
-  const phentsize = reader.u16(wide ? 54 : 42);
-  const phnum = reader.u16(wide ? 56 : 44);
-  const shentsize = reader.u16(wide ? 58 : 46);
-  const shnum = reader.u16(wide ? 60 : 48);
-  const shstrndx = reader.u16(wide ? 62 : 50);
+  const raw = readElfRawTableDeclarations(bytes, header);
+  if (!raw.ok) return fail(raw.error.message);
+  const { programs, sections } = raw.value;
+  if (
+    programs.offset > BigInt(Number.MAX_SAFE_INTEGER) ||
+    sections.offset > BigInt(Number.MAX_SAFE_INTEGER)
+  )
+    return fail("ELF offset or size exceeds a safe integer.");
+  const phoff = Number(programs.offset);
+  const shoff = Number(sections.offset);
+  const phentsize = programs.width;
+  const phnum = programs.count;
+  const shentsize = sections.width;
+  const shnum = sections.count;
+  const shstrndx = sections.namesIndex;
   if (
     phnum === 0xffff ||
     shnum === 0xffff ||

src/native/pwntools/RecordedCrashStructureBindings.test.ts

@@ -50,3 +50,14 @@ it.each([3, 0x46494c45])(
     expect(recordedCrashSchema.safeParse(report).success).toBe(false);
   },
 );
+
+it("keeps snapshot rebinding independent of unused ELF section and header-size admission", () => {
+  const report = recordedCrashSchema.parse(recordedCrashFixture());
+  const bytes = recordedCrashFixtureBytes(report);
+  bytes.writeUInt16LE(0, 52);
+  bytes.writeBigUInt64LE(0xffffffffffffffffn, 40);
+  bytes.writeUInt16LE(0xffff, 60);
+  expect(() =>
+    validateRecordedCrashStructure(report, bytes, report.decoder_diagnostics),
+  ).not.toThrow();
+});

src/native/pwntools/RecordedCrashStructureBindings.ts

@@ -1,3 +1,4 @@
+import { readElfRawTableDeclarations } from "../../domain/elfRawTableDeclarations.js";
 import { AnalysisOutputError } from "../../domain/analysisErrorCore.js";
 import {
   RECORDED_LINUX_CORE_PROFILES,
@@ -103,12 +104,18 @@ export function validateRecordedCrashStructure(
     header.readUInt16LE(18) !== expectedMachine
   )
     fail();
-  const table = header.readBigUInt64LE(32);
-  const entryBytes = header.readUInt16LE(54);
-  let count = header.readUInt16LE(56);
+  const rawTables = readElfRawTableDeclarations(header, {
+    elfClass: 64,
+    byteOrder: "little",
+  });
+  if (!rawTables.ok) return fail();
+  const { programs, sections } = rawTables.value;
+  const table = programs.offset;
+  const entryBytes = programs.width;
+  let count = programs.count;
   if (count === 0xffff) {
-    if (header.readUInt16LE(58) < 64) return fail();
-    count = bytesAt(header.readBigUInt64LE(40), 64).readUInt32LE(44);
+    if (sections.width < 64) return fail();
+    count = bytesAt(sections.offset, 64).readUInt32LE(44);
   }
   if (count !== report.segments.length || (count > 0 && entryBytes < 56))
     fail();