[PATCH v3] libiberty: Check zero value shstrndx in simple-object-elf.c

[Ren Kimura]

This patch fixes a Bug 90924.
simple_object_elf functions don't load section table 0 of ELF file, which is 
not a useful.
However If e_shstrndx in ELF header points to a section table 0 (i.e. 
e_shstrndx == 0), a calculation of offset to string section table causes 
integer overflow at every line "(eor->shstrndx - 1)".
A result becomes negative value (unsigned int)-1 and causes memory corruption.

Signed-off-by: Ren Kimura <rkx1209...@gmail.com>
---
 libiberty/ChangeLog           |  5 +++++
 libiberty/simple-object-elf.c | 10 +++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/libiberty/ChangeLog b/libiberty/ChangeLog
index c3daf2ae8c8..ea2f3e6a982 100644
--- a/libiberty/ChangeLog
+++ b/libiberty/ChangeLog
@@ -1,3 +1,8 @@
+2019-07-12  Ren Kimura  <rkx1209...@gmail.com>
+
+       * simple-object-elf.c (simple_object_elf_match): Check zero value 
shstrndx.
+       This fixes a Bug 90924.
+
 2019-05-31  Michael Forney  <mfor...@mforney.org>
 
        * cp-demangle.c: Don't define CP_DYNAMIC_ARRAYS if __STDC_NO_VLA__
diff --git a/libiberty/simple-object-elf.c b/libiberty/simple-object-elf.c
index 22c9ae7ed2d..9c561632bc5 100644
--- a/libiberty/simple-object-elf.c
+++ b/libiberty/simple-object-elf.c
@@ -548,7 +548,15 @@ simple_object_elf_match (unsigned char 
header[SIMPLE_OBJECT_MATCH_HEADER_LEN],
       XDELETE (eor);
       return NULL;
     }
-
+  
+  if (eor->shstrndx == 0)
+    {
+      *errmsg = "invalid ELF shstrndx == 0";
+      *err = 0;
+      XDELETE (eor);
+      return NULL;
+    }
+  
   return (void *) eor;
 }
 
-- 
2.19.1