Re: [PATCH v3] kernel/module: Fix mem leak in module_add_modinfo_attrs

From: Jessica Yu
Date: Fri Jun 07 2019 - 10:07:08 EST

+++ Miroslav Benes [04/06/19 12:46 +0200]:
On Mon, 3 Jun 2019, YueHaibing wrote:

In module_add_modinfo_attrs if sysfs_create_file
fails, we forget to free allocated modinfo_attrs
and roll back the sysfs files.

Fixes: 03e88ae1b13d ("[PATCH] fix module sysfs files reference counting")
Signed-off-by: YueHaibing <yuehaibing@xxxxxxxxxx>
v3: reuse module_remove_modinfo_attrs
v2: free from '--i' instead of 'i--'
kernel/module.c | 21 ++++++++++++++++-----
1 file changed, 16 insertions(+), 5 deletions(-)

I'm afraid it is not completely correct.

diff --git a/kernel/module.c b/kernel/module.c
index 80c7c09..c6b8912 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1697,6 +1697,8 @@ static int add_usage_links(struct module *mod)
return ret;

+static void module_remove_modinfo_attrs(struct module *mod, int end);
static int module_add_modinfo_attrs(struct module *mod)
struct module_attribute *attr;
@@ -1711,24 +1713,33 @@ static int module_add_modinfo_attrs(struct module *mod)
return -ENOMEM;

temp_attr = mod->modinfo_attrs;
- for (i = 0; (attr = modinfo_attrs[i]) && !error; i++) {
+ for (i = 0; (attr = modinfo_attrs[i]); i++) {
if (!attr->test || attr->test(mod)) {
memcpy(temp_attr, attr, sizeof(*temp_attr));
error = sysfs_create_file(&mod->mkobj.kobj,
+ if (error)
+ goto error_out;

sysfs_create_file() failed, so we need to clear all previously processed
attrs and not the current one.

+ return 0;
+ module_remove_modinfo_attrs(mod, --i);

It says "call sysfs_remove_file() on all attrs ending with --i included
(all correctly processed attrs).

return error;

-static void module_remove_modinfo_attrs(struct module *mod)
+static void module_remove_modinfo_attrs(struct module *mod, int end)
struct module_attribute *attr;
int i;

for (i = 0; (attr = &mod->modinfo_attrs[i]); i++) {
+ if (end >= 0 && i > end)
+ break;

If end == 0, you break the loop without calling sysfs_remove_file(), which
is a bug if you called module_remove_modinfo_attrs(mod, 0).

Calling module_remove_modinfo_attrs(mod, i); in module_add_modinfo_attrs()
under error_out label and changing the condition here to

if (end >= 0 && i >= end)

should work as expected.

But let me ask another question and it might be more to Jessica. Why is
there even a call to attr->free(mod); (if it exists) in
module_remove_modinfo_attrs()? The same is in free_modinfo() (as opposed
to setup_modinfo() where attr->setup(mod) is called. Is it because
free_modinfo() is called only in load_module()'s error path, while
module_remove_modinfo_attrs() is called even in free_module() path?

kfree() checks for NULL pointer, so there is no bug, but it is certainly
not nice and it calls for cleanup. But I may be missing something.

No, you are right in that it is a bit clumsy and and the sysfs error
path handling is asymmetrical. I think it could be cleaned up a bit.

IMO, I think the attr->free() calls should either be (1) removed from
module_remove_modinfo_attrs() as free_modinfo() takes care of that,
otherwise we could potentially call attr->free() twice (once in the
internal error handling of mod_sysfs_setup() and once again in the
free_modinfo: label in load_module()) or option (2) would be to merge
the attr->setup() calls into module_add_modinfo_attrs() so that it is
symmetrical to module_remove_modinfo_attrs(). I'm leaning towards
option 2 but have not carefully checked yet if moving the
attr->setup() calls into module_add_modinfo_attrs() would break
anything. In any case I will prepare some cleanup patches for this.