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SubjectRe: [PATCH/RFC] alternative aproach to: Ban module license tag string termination trick
On Sat, Feb 03, 2007 at 03:08:14AM +0100, Bodo Eggert wrote:
> This patch changes the module license handling code to:
> - prevent the "GPL\0 for nothing"-trick

You can achieve this effect without changing the existing module
format, and it's far more difficult to bypass with build-with-
modified module.h tricks.

--- a/kernel/module.c Mon Nov 7 19:58:31 2005
+++ b/kernel/module.c Mon Dec 5 19:39:36 2005
@@ -286,6 +286,24 @@ static unsigned long find_local_symbol(E
return 0;
}

+static int check_modinfo_objects(Elf_Shdr *sechdrs,
+ unsigned int symindex,
+ unsigned int infoindex)
+{
+ unsigned int i;
+ Elf_Sym *sym = (void *)sechdrs[symindex].sh_addr;
+ char *info = (char *)sechdrs[infoindex].sh_addr;
+
+ for (i = 1; i < sechdrs[symindex].sh_size/sizeof(*sym); i++) {
+ if (sym[i].st_shndx == infoindex &&
+ ELF_ST_TYPE(sym[i].st_info) == STT_OBJECT) {
+ if (strlen(info + sym[i].st_value) + 1 != sym[i].st_size)
+ return -ENOEXEC;
+ }
+ }
+ return 0;
+}
+
/* Search for module by name: must hold module_mutex. */
static struct module *find_module(const char *name)
{
@@ -1674,6 +1692,10 @@ static struct module *load_module(void _
goto free_hdr;
}

+ err = check_modinfo_objects(sechdrs, symindex, infoindex);
+ if (err)
+ goto free_hdr;
+
modmagic = get_modinfo(sechdrs, infoindex, "vermagic");
/* This is allowed: modprobe --force will invalidate it. */
if (!modmagic) {
--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of:
-
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