elflint: Don't trust sh_entsize when checking hash sections.

Calculate and use the expected entsize instead of relying on the one
given by the ELF file section header. Return early if there isn't enough
data in the section to check the full hash table.

https://sourceware.org/bugzilla/show_bug.cgi?id=21311

Signed-off-by: Mark Wielaard <[email protected]>

2 files changed, 27 insertions, 12 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 6031213f..70744bcf 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,12 @@
 2017-03-27  Mark Wielaard  <[email protected]>
 
+	* elflint.c (check_sysv_hash): Return early if section size is
+	too small.
+	(check_sysv_hash64): Likewise.
+	(check_hash): Calculate expect_entsize to check section size.
+
+2017-03-27  Mark Wielaard  <[email protected]>
+
 	* elflint.c (check_symtab_shndx): Check data->d_size.
 
 2017-03-24  Mark Wielaard  <[email protected]>
diff --git a/src/elflint.c b/src/elflint.c
index 76fb1a0c..5e95ca95 100644
--- a/src/elflint.c
+++ b/src/elflint.c
@@ -1,5 +1,5 @@
 /* Pedantic checking of ELF files compliance with gABI/psABI spec.
-   Copyright (C) 2001-2015 Red Hat, Inc.
+   Copyright (C) 2001-2015, 2017 Red Hat, Inc.
    This file is part of elfutils.
    Written by Ulrich Drepper <[email protected]>, 2001.
 
@@ -1993,11 +1993,14 @@ check_sysv_hash (Ebl *ebl, GElf_Shdr *shdr, Elf_Data *data, int idx,
   Elf32_Word nbucket = ((Elf32_Word *) data->d_buf)[0];
   Elf32_Word nchain = ((Elf32_Word *) data->d_buf)[1];
 
-  if (shdr->sh_size < (2 + nbucket + nchain) * shdr->sh_entsize)
-    ERROR (gettext ("\
+  if (shdr->sh_size < (2 + nbucket + nchain) * sizeof (Elf32_Word))
+    {
+      ERROR (gettext ("\
 section [%2d] '%s': hash table section is too small (is %ld, expected %ld)\n"),
-	   idx, section_name (ebl, idx), (long int) shdr->sh_size,
-	   (long int) ((2 + nbucket + nchain) * shdr->sh_entsize));
+	     idx, section_name (ebl, idx), (long int) shdr->sh_size,
+	     (long int) ((2 + nbucket + nchain) * sizeof (Elf32_Word)));
+      return;
+    }
 
   size_t maxidx = nchain;
 
@@ -2044,11 +2047,14 @@ check_sysv_hash64 (Ebl *ebl, GElf_Shdr *shdr, Elf_Data *data, int idx,
   Elf64_Xword nbucket = ((Elf64_Xword *) data->d_buf)[0];
   Elf64_Xword nchain = ((Elf64_Xword *) data->d_buf)[1];
 
-  if (shdr->sh_size < (2 + nbucket + nchain) * shdr->sh_entsize)
-    ERROR (gettext ("\
+  if (shdr->sh_size < (2 + nbucket + nchain) * sizeof (Elf64_Xword))
+    {
+      ERROR (gettext ("\
 section [%2d] '%s': hash table section is too small (is %ld, expected %ld)\n"),
-	   idx, section_name (ebl, idx), (long int) shdr->sh_size,
-	   (long int) ((2 + nbucket + nchain) * shdr->sh_entsize));
+	     idx, section_name (ebl, idx), (long int) shdr->sh_size,
+	     (long int) ((2 + nbucket + nchain) * sizeof (Elf64_Xword)));
+      return;
+    }
 
   size_t maxidx = nchain;
 
@@ -2288,10 +2294,12 @@ section [%2d] '%s': hash table not for dynamic symbol table\n"),
 section [%2d] '%s': invalid sh_link symbol table section index [%2d]\n"),
 	   idx, section_name (ebl, idx), shdr->sh_link);
 
-  if (shdr->sh_entsize != (tag == SHT_GNU_HASH
+  size_t expect_entsize = (tag == SHT_GNU_HASH
 			   ? (gelf_getclass (ebl->elf) == ELFCLASS32
 			      ? sizeof (Elf32_Word) : 0)
-			   : (size_t) ebl_sysvhash_entrysize (ebl)))
+			   : (size_t) ebl_sysvhash_entrysize (ebl));
+
+  if (shdr->sh_entsize != expect_entsize)
     ERROR (gettext ("\
 section [%2d] '%s': hash table entry size incorrect\n"),
 	   idx, section_name (ebl, idx));
@@ -2300,7 +2308,7 @@ section [%2d] '%s': hash table entry size incorrect\n"),
     ERROR (gettext ("section [%2d] '%s': not marked to be allocated\n"),
 	   idx, section_name (ebl, idx));
 
-  if (shdr->sh_size < (tag == SHT_GNU_HASH ? 4 : 2) * (shdr->sh_entsize ?: 4))
+  if (shdr->sh_size < (tag == SHT_GNU_HASH ? 4 : 2) * (expect_entsize ?: 4))
     {
       ERROR (gettext ("\
 section [%2d] '%s': hash table has not even room for initial administrative entries\n"),