Messages in this thread Patch in this message | | | Date | Fri, 7 Jun 2019 16:02:50 +0200 | From | Jessica Yu <> | Subject | Re: [PATCH v3] kernel/module: Fix mem leak in module_add_modinfo_attrs |
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+++ 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@huawei.com> >> --- >> 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)); >> sysfs_attr_init(&temp_attr->attr); >> error = sysfs_create_file(&mod->mkobj.kobj, >> &temp_attr->attr); >> + if (error) >> + goto error_out; > >sysfs_create_file() failed, so we need to clear all previously processed >attrs and not the current one. > >> ++temp_attr; >> } >> } >> + >> + return 0; >> + >> +error_out: >> + 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) > break; > >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.
Thanks!
Jessica
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