[patch] nm: minimal section header size

[Sébastien Marie]

Hi,

This patch ensure that e_shentsize (sections header's size in bytes) is
big enough to fill at least one Elf_Shdr.

Please note, I am not completely sure to have understand this part:
calloc() is called with a dynamic element size (e_shentsize: readed for
file), but the variable is declared as Elf_Shdr[] (array of Elf_Shdr:
which is a fixed element size).

While here, inverts calloc() arguments to be calloc(nmemb, size),
according to fread() call after.

This problem was found with afl, when e_shentsize was 1.
-- 
Sébastien Marie


Index: b/usr.bin/nm/elf.c
===================================================================
--- a/usr.bin/nm/elf.c  2015-06-19 06:26:13.704127213 +0200
+++ b/usr.bin/nm/elf.c  2015-06-19 06:48:58.806582243 +0200
@@ -159,7 +159,12 @@
                return (NULL);
        }
 
-       if ((shdr = calloc(head->e_shentsize, head->e_shnum)) == NULL) {
+       if (head->e_shentsize < sizeof(Elf_Shdr)) {
+               warnx("%s: inconsistent section header size", name);
+               return (NULL);
+       }
+
+       if ((shdr = calloc(head->e_shnum, head->e_shentsize)) == NULL) {
                warn("%s: malloc shdr", name);
                return (NULL);
        }