asan: buffer overflow in elf32_arm_get_synthetic_symtab

[Alan Modra <amodra@gmail.com>]

Guard against fuzzed files where .plt size isn't commensurate with
plt relocations.

	* elf32-arm.c (elf32_arm_plt0_size): Add data_size param.
	Return -1 if data_size is too small.
	(elf32_arm_plt_size): Likewise.  Delete temp var.  Formatting.
	(elf32_arm_get_synthetic_symtab): Adjust to suit.

diff --git a/bfd/elf32-arm.c b/bfd/elf32-arm.c
index f3ad270a6a0..18c30dbef86 100644
--- a/bfd/elf32-arm.c
+++ b/bfd/elf32-arm.c
@@ -19971,11 +19971,15 @@ read_code16 (const bfd *abfd, const bfd_byte *addr)
    or (bfd_vma) -1 if size can not be determined.  */
 
 static bfd_vma
-elf32_arm_plt0_size (const bfd *abfd, const bfd_byte *addr)
+elf32_arm_plt0_size (const bfd *abfd, const bfd_byte *addr,
+		     bfd_size_type data_size)
 {
   bfd_vma first_word;
   bfd_vma plt0_size;
 
+  if (data_size < 4)
+    return (bfd_vma) -1;
+
   first_word = read_code32 (abfd, addr);
 
   if (first_word == elf32_arm_plt0_entry[0])
@@ -19994,24 +19998,28 @@ elf32_arm_plt0_size (const bfd *abfd, const bfd_byte *addr)
    or (bfd_vma) -1 if size can not be determined.  */
 
 static bfd_vma
-elf32_arm_plt_size (const bfd *abfd, const bfd_byte *start, bfd_vma offset)
+elf32_arm_plt_size (const bfd *abfd, const bfd_byte *start, bfd_vma offset,
+		    bfd_size_type data_size)
 {
   bfd_vma first_insn;
   bfd_vma plt_size = 0;
-  const bfd_byte *addr = start + offset;
 
   /* PLT entry size if fixed on Thumb-only platforms.  */
   if (read_code32 (abfd, start) == elf32_thumb2_plt0_entry[0])
-      return 4 * ARRAY_SIZE (elf32_thumb2_plt_entry);
+    return 4 * ARRAY_SIZE (elf32_thumb2_plt_entry);
 
   /* Respect Thumb stub if necessary.  */
-  if (read_code16 (abfd, addr) == elf32_arm_plt_thumb_stub[0])
+  if (offset + 2 > data_size)
+    return (bfd_vma) -1;
+  if (read_code16 (abfd, start + offset) == elf32_arm_plt_thumb_stub[0])
     {
       plt_size += 2 * ARRAY_SIZE (elf32_arm_plt_thumb_stub);
     }
 
   /* Strip immediate from first add.  */
-  first_insn = read_code32 (abfd, addr + plt_size) & 0xffffff00;
+  if (offset + plt_size + 4 > data_size)
+    return (bfd_vma) -1;
+  first_insn = read_code32 (abfd, start + offset + plt_size) & 0xffffff00;
 
 #ifdef FOUR_WORD_PLT
   if (first_insn == elf32_arm_plt_entry[0])
@@ -20088,7 +20096,7 @@ elf32_arm_get_synthetic_symtab (bfd *abfd,
 	size += sizeof ("+0x") - 1 + 8;
     }
 
-  offset = elf32_arm_plt0_size (abfd, data);
+  offset = elf32_arm_plt0_size (abfd, data, plt->size);
   if (offset == (bfd_vma) -1
       || (s = *ret = (asymbol *) bfd_malloc (size)) == NULL)
     {
@@ -20103,7 +20111,7 @@ elf32_arm_get_synthetic_symtab (bfd *abfd,
     {
       size_t len;
 
-      bfd_vma plt_size = elf32_arm_plt_size (abfd, data, offset);
+      bfd_vma plt_size = elf32_arm_plt_size (abfd, data, offset, plt->size);
       if (plt_size == (bfd_vma) -1)
 	break;
 

-- 
Alan Modra
Australia Development Lab, IBM