[Object/ELF] - Check that e_shnum is null when e_shoff is.

Spec says (http://www.sco.com/developers/gabi/1998-04-29/ch4.eheader.html) :
e_shnum
This member holds the number of entries in the section header table. Thus the product of e_shentsize and e_shnum gives the section header table's size in bytes. If a file has no section header table, e_shnum holds the value zero.

Revealed using "id_000037,sig_11,src_000015,op_havoc,rep_8" from PR30540

That was the reason of crash in lld on incorrect input file.
Binary reduced using afl-min.

Differential revision: https://reviews.llvm.org/D25090

llvm-svn: 284371

3 files changed, 8 insertions, 1 deletions

diff --git a/llvm/include/llvm/Object/ELF.h b/llvm/include/llvm/Object/ELF.h
index 31f42f5f50c..03b172fe304 100644
--- a/llvm/include/llvm/Object/ELF.h
+++ b/llvm/include/llvm/Object/ELF.h
@@ -319,8 +319,12 @@ ELFFile<ELFT>::ELFFile(StringRef Object, std::error_code &EC)
 
   Header = reinterpret_cast<const Elf_Ehdr *>(base());
 
-  if (Header->e_shoff == 0)
+  if (Header->e_shoff == 0) {
+    if (Header->e_shnum != 0)
+      report_fatal_error(
+          "e_shnum should be zero if a file has no section header table");
     return;
+  }
 
   const uint64_t SectionTableOffset = Header->e_shoff;
 
diff --git a/llvm/test/Object/Inputs/invalid-e_shnum.elf b/llvm/test/Object/Inputs/invalid-e_shnum.elf
new file mode 100644
index 00000000000..0b46fbd8cec
--- /dev/null
+++ b/llvm/test/Object/Inputs/invalid-e_shnum.elf
diff --git a/llvm/test/Object/invalid.test b/llvm/test/Object/invalid.test
index d940789b6dc..c72de062059 100644
--- a/llvm/test/Object/invalid.test
+++ b/llvm/test/Object/invalid.test
@@ -55,6 +55,9 @@ INVALID-SYMTAB-SIZE: Invalid data was encountered while parsing the file
 RUN: not llvm-readobj -t %p/Inputs/invalid-xindex-size.elf 2>&1 | FileCheck --check-prefix=INVALID-XINDEX-SIZE %s
 INVALID-XINDEX-SIZE: Invalid data was encountered while parsing the file.
 
+RUN: not llvm-readobj -t %p/Inputs/invalid-e_shnum.elf 2>&1 | FileCheck --check-prefix=INVALID-SH-NUM %s
+INVALID-SH-NUM: e_shnum should be zero if a file has no section header table
+
 RUN: not llvm-readobj -t %p/Inputs/invalid-ext-symtab-index.elf-x86-64 2>&1 | \
 RUN:   FileCheck --check-prefix=INVALID-EXT-SYMTAB-INDEX %s
 INVALID-EXT-SYMTAB-INDEX: Invalid symbol table index