kbuild: fix segfault in modpost

Fix modpost segfault.

Before:
-------
ynezz@ntbk:~/linux-2.6.git$ scripts/mod/modpost vmlinux ath_pci.o
Segmentation fault

After:
------
ynezz@ntbk:~/linux-2.6.git$ scripts/mod/modpost vmlinux ath_pci.o
FATAL: section header offset=815726848 in file 'ath_pci.o' is bigger then filesize=153968

Sam: This seems to warn for a binutils issue. Anyway modpost should not
segfault.

Signed-off-by: Petr Stetiar <ynezz@true.cz>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

scripts/mod/modpost.c

@@ -381,6 +381,12 @@ static int parse_elf(struct elf_info *info, const char *filename)
 	sechdrs = (void *)hdr + hdr->e_shoff;
 	info->sechdrs = sechdrs;
 
+	/* Check if file offset is correct */
+	if (hdr->e_shoff > info->size) {
+		fatal("section header offset=%u in file '%s' is bigger then filesize=%lu\n", hdr->e_shoff, filename, info->size);
+		return 0;
+	}
+
 	/* Fix endianness in section headers */
 	for (i = 0; i < hdr->e_shnum; i++) {
 		sechdrs[i].sh_type   = TO_NATIVE(sechdrs[i].sh_type);