Re: [PATCH 2/2] module: Add module name to modinfo

From: Jessica Yu
Date: Fri Apr 21 2017 - 02:28:21 EST


+++ Kees Cook [12/04/17 16:16 -0700]:
Accessing the mod structure (e.g. for mod->name) prior to having completed
check_modstruct_version() can result in writing garbage to the error logs
if the layout of the mod structure loaded from disk doesn't match the
running kernel's mod structure layout. This kind of mismatch will become
much more likely if a kernel is built with different randomization seed
for the struct layout randomization plugin.

Instead, add and use a new modinfo string for logging the module name.

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
kernel/module.c | 21 ++++++++++++++-------
scripts/mod/modpost.c | 1 +
2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index ed6cf2367217..ed4a399174ba 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -299,6 +299,7 @@ int unregister_module_notifier(struct notifier_block *nb)
EXPORT_SYMBOL(unregister_module_notifier);

struct load_info {
+ char *name;
Elf_Ehdr *hdr;
unsigned long len;
Elf_Shdr *sechdrs;
@@ -1297,12 +1298,12 @@ static int check_version(const struct load_info *info,
}

/* Broken toolchain. Warn once, then let it go.. */
- pr_warn_once("%s: no symbol version for %s\n", mod->name, symname);
+ pr_warn_once("%s: no symbol version for %s\n", info->name, symname);
return 1;

bad_version:
pr_warn("%s: disagrees about version of symbol %s\n",
- mod->name, symname);
+ info->name, symname);
return 0;
}

@@ -2892,9 +2893,15 @@ static int rewrite_section_headers(struct load_info *info, int flags)
info->index.vers = 0; /* Pretend no __versions section! */
else
info->index.vers = find_sec(info, "__versions");
+ info->sechdrs[info->index.vers].sh_flags &= ~(unsigned long)SHF_ALLOC;
+
info->index.info = find_sec(info, ".modinfo");
+ if (!info->index.info)
+ info->name = "unknown";
+ else
+ info->name = get_modinfo(info, "name");

Hm, if we attempt to load an old module without the new name field
(i.e. all modules currently), we'll end up printing "(null)" for all
the prints that use info->name. Maybe we can fall back to mod->name if
the name field isn't there and the kernel wasn't compiled with the
randstruct plugin?

info->sechdrs[info->index.info].sh_flags &= ~(unsigned long)SHF_ALLOC;
- info->sechdrs[info->index.vers].sh_flags &= ~(unsigned long)SHF_ALLOC;
+
return 0;
}

@@ -2934,14 +2941,14 @@ static struct module *setup_load_info(struct load_info *info, int flags)

info->index.mod = find_sec(info, ".gnu.linkonce.this_module");
if (!info->index.mod) {
- pr_warn("No module found in object\n");
+ pr_warn("%s: No module found in object\n", info->name);
return ERR_PTR(-ENOEXEC);
}
/* This is temporary: point mod into copy of data. */
mod = (void *)info->sechdrs[info->index.mod].sh_addr;

if (info->index.sym == 0) {
- pr_warn("%s: module has no symbols (stripped?)\n", mod->name);
+ pr_warn("%s: module has no symbols (stripped?)\n", info->name);
return ERR_PTR(-ENOEXEC);
}

@@ -2969,7 +2976,7 @@ static int check_modinfo(struct module *mod, struct load_info *info, int flags)
return err;
} else if (!same_magic(modmagic, vermagic, info->index.vers)) {
pr_err("%s: version magic '%s' should be '%s'\n",
- mod->name, modmagic, vermagic);
+ info->name, modmagic, vermagic);
return -ENOEXEC;
}


Maybe we want to use info->name for the blacklisted() check as well (see
layout_and_allocate()).

@@ -3622,7 +3629,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
if (!mod->sig_ok) {
pr_notice_once("%s: module verification failed: signature "
"and/or required key missing - tainting "
- "kernel\n", mod->name);
+ "kernel\n", info->name);
add_taint_module(mod, TAINT_UNSIGNED_MODULE, LOCKDEP_STILL_OK);
}

Do we still need to use info->name here? At this point we're done with
layout_and_allocate(), plus the modstruct check and vermagic check, and mod
should be pointing to its new place in memory.

#endif
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 30d752a4a6a6..48397feb08fb 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -2126,6 +2126,7 @@ static void add_header(struct buffer *b, struct module *mod)
buf_printf(b, "#include <linux/compiler.h>\n");
buf_printf(b, "\n");
buf_printf(b, "MODULE_INFO(vermagic, VERMAGIC_STRING);\n");
+ buf_printf(b, "MODULE_INFO(name, KBUILD_MODNAME);\n");
buf_printf(b, "\n");
buf_printf(b, "__visible struct module __this_module\n");
buf_printf(b, "__attribute__((section(\".gnu.linkonce.this_module\"))) = {\n");
--
2.7.4