Check sh_type for symbol table and finish ProcessDIEs if any DIE processing goes wrong

- If symbol table section is malformed, skip them.
- SkipDIE and ProcessDIE return nullptr when processing goes wrong due to malformed debug info, stop processing in this case.

Bug: 1349354
Change-Id: Ia1d3e3591bbd2dad8b9eb351c1882cfc03bfad4b
Reviewed-on: https://chromium-review.googlesource.com/c/breakpad/breakpad/+/3821448
Reviewed-by: Joshua Peraza <jperaza@chromium.org>

src/common/dwarf/dwarf2reader.cc

@@ -953,8 +953,22 @@ void CompilationUnit::ProcessDIEs() {
     const enum DwarfTag tag = abbrev.tag;
     if (!handler_->StartDIE(absolute_offset, tag)) {
       dieptr = SkipDIE(dieptr, abbrev);
+      if (!dieptr) {
+        fprintf(stderr,
+                "An error happens when skipping a DIE's attributes at offset "
+                "%lx. Stopped processing following DIEs in this CU.\n",
+                absolute_offset);
+        exit(1);
+      }
     } else {
       dieptr = ProcessDIE(absolute_offset, dieptr, abbrev);
+      if (!dieptr) {
+        fprintf(stderr,
+                "An error happens when processing a DIE at offset %lx. Stopped "
+                "processing following DIEs in this CU.\n",
+                absolute_offset);
+        exit(1);
+      }
     }
 
     if (abbrev.has_children) {

src/common/dwarf/elf_reader.cc

@@ -196,6 +196,17 @@ class ElfSectionReader {
     // to process its contents.
     if (header_.sh_type == SHT_NOBITS || header_.sh_size == 0)
       return;
+    // extra sh_type check for string table.
+    if ((std::strcmp(name, ".strtab") == 0 ||
+         std::strcmp(name, ".shstrtab") == 0) &&
+        header_.sh_type != SHT_STRTAB) {
+      fprintf(stderr,
+              "Invalid sh_type for string table section: expected "
+              "SHT_STRTAB or SHT_DYNSYM, but got %d\n",
+              header_.sh_type);
+      return;
+    }
+
     contents_aligned_ = mmap(NULL, size_aligned_, PROT_READ, MAP_SHARED,
                              fd, offset_aligned);
     // Set where the offset really should begin.
@@ -877,7 +888,7 @@ class ElfReaderImpl {
     if (reader == NULL)
       reader = new ElfSectionReader<ElfArch>(name, path_, fd_,
                                              section_headers_[num]);
-    return reader;
+    return reader->contents() ? reader : nullptr;
   }
 
   // Parse out the overall header information from the file and assert