[PATCH v2 1/7] modules: Create rlimit for module space

Rick Edgecombe
2018-10-11T23:31:11Z

This introduces a new rlimit, RLIMIT_MODSPACE, which limits the amount of
module space a user can use. The intention is to be able to limit module space
allocations that may come from un-privlidged users inserting e/BPF filters.

There is unfortunately no cross platform place to perform this accounting
during allocation in the module space, so instead two helpers are created to be
inserted into the various arch’s that implement module_alloc. These
helpers perform the checks and help with tracking. The intention is that they
an be added to the various arch’s as easily as possible.

Since filters attached to sockets can be passed to other processes via domain
sockets and freed there, there is new tracking for the uid of each allocation.
This way if the allocation is freed by a different user, it will not throw off
the accounting.

For decrementing the module space usage when an area is free, there is a
cross-platform place to do this. The behavior is that if the helpers to
increment and check are not added into an arch’s module_alloc, then the
decrement should have no effect. This is due to the allocation being missing
from the allocation-uid tracking.

Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
fs/proc/base.c | 1 +
include/asm-generic/resource.h | 8 ++
include/linux/moduleloader.h | 3 +
include/linux/sched/user.h | 4 +
include/uapi/asm-generic/resource.h | 3 +-
kernel/module.c | 141 +++++++++++++++++++++++++++-
6 files changed, 158 insertions(+), 2 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 7e9f07bf260d..84824f50e9f8 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -562,6 +562,7 @@ static const struct limit_names lnames[RLIM_NLIMITS] = {
[RLIMIT_NICE] = {"Max nice priority", NULL},
[RLIMIT_RTPRIO] = {"Max realtime priority", NULL},
[RLIMIT_RTTIME] = {"Max realtime timeout", "us"},
+ [RLIMIT_MODSPACE] = {"Max module space", "bytes"},
};

/* Display limits for a process */
diff --git a/include/asm-generic/resource.h b/include/asm-generic/resource.h
index 8874f681b056..94c150e3dd12 100644
--- a/include/asm-generic/resource.h
+++ b/include/asm-generic/resource.h
@@ -4,6 +4,13 @@

#include <uapi/asm-generic/resource.h>

+/*
+ * If the module space rlimit is not defined in an arch specific way, leave
+ * room for 10000 large eBPF filters.
+ */
+#ifndef MODSPACE_LIMIT
+#define MODSPACE_LIMIT (5*PAGE_SIZE*10000)
+#endif

/*
* boot-time rlimit defaults for the init task:
@@ -26,6 +33,7 @@
[RLIMIT_NICE] = { 0, 0 }, \
[RLIMIT_RTPRIO] = { 0, 0 }, \
[RLIMIT_RTTIME] = { RLIM_INFINITY, RLIM_INFINITY }, \
+ [RLIMIT_MODSPACE] = { MODSPACE_LIMIT, MODSPACE_LIMIT }, \
}

#endif
diff --git a/include/linux/moduleloader.h b/include/linux/moduleloader.h
index 31013c2effd3..206539e97579 100644
--- a/include/linux/moduleloader.h
+++ b/include/linux/moduleloader.h
@@ -86,6 +86,9 @@ void module_arch_cleanup(struct module *mod);
/* Any cleanup before freeing mod->module_init */
void module_arch_freeing_init(struct module *mod);

+int check_inc_mod_rlimit(unsigned long size);
+void update_mod_rlimit(void *addr, unsigned long size);
+
#ifdef CONFIG_KASAN
#include <linux/kasan.h>
#define MODULE_ALIGN (PAGE_SIZE << KASAN_SHADOW_SCALE_SHIFT)
diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
index 39ad98c09c58..4c6d99d066fe 100644
--- a/include/linux/sched/user.h
+++ b/include/linux/sched/user.h
@@ -44,6 +44,10 @@ struct user_struct {
atomic_long_t locked_vm;
#endif

+#ifdef CONFIG_MODULES
+ atomic_long_t module_vm;
+#endif
+
/* Miscellaneous per-user rate limit */
struct ratelimit_state ratelimit;
};
diff --git a/include/uapi/asm-generic/resource.h b/include/uapi/asm-generic/resource.h
index f12db7a0da64..3f998340ed30 100644
--- a/include/uapi/asm-generic/resource.h
+++ b/include/uapi/asm-generic/resource.h
@@ -46,7 +46,8 @@
0-39 for nice level 19 .. -20 */
#define RLIMIT_RTPRIO 14 /* maximum realtime priority */
#define RLIMIT_RTTIME 15 /* timeout for RT tasks in us */
-#define RLIM_NLIMITS 16
+#define RLIMIT_MODSPACE 16 /* max module space address usage */
+#define RLIM_NLIMITS 17

/*
* SuS says limits have to be unsigned.
diff --git a/kernel/module.c b/kernel/module.c
index 6746c85511fe..2ef9ed95bf60 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2110,9 +2110,139 @@ static void free_module_elf(struct module *mod)
}
#endif /* CONFIG_LIVEPATCH */

+struct mod_alloc_user {
+ struct rb_node node;
+ unsigned long addr;
+ unsigned long pages;
+ kuid_t uid;
+};
+
+static struct rb_root alloc_users = RB_ROOT;
+static DEFINE_SPINLOCK(alloc_users_lock);
+
+static unsigned int get_mod_page_cnt(unsigned long size)
+{
+ /* Add one for guard page */
+ return (PAGE_ALIGN(size) >> PAGE_SHIFT) + 1;
+}
+
+void update_mod_rlimit(void *addr, unsigned long size)
+{
+ unsigned long addrl = (unsigned long) addr;
+ struct rb_node **new = &(alloc_users.rb_node), *parent = NULL;
+ struct mod_alloc_user *track = kmalloc(sizeof(struct mod_alloc_user),
+ GFP_KERNEL);
+ unsigned int pages = get_mod_page_cnt(size);
+
+ /*
+ * If addr is NULL, then we need to reverse the earlier increment that
+ * would have happened in an check_inc_mod_rlimit call.
+ */
+ if (!addr) {
+ struct user_struct *user = get_current_user();
+
+ atomic_long_sub(pages, &user->module_vm);
+ free_uid(user);
+ return;
+ }
+
+ /* Now, add tracking for the uid that allocated this */
+ track->uid = current_uid();
+ track->addr = addrl;
+ track->pages = pages;
+
+ spin_lock(&alloc_users_lock);
+
+ while (*new) {
+ struct mod_alloc_user *cur =
+ rb_entry(*new, struct mod_alloc_user, node);
+ parent = *new;
+ if (cur->addr > addrl)
+ new = &(*new)->rb_left;
+ else
+ new = &(*new)->rb_right;
+ }
+
+ rb_link_node(&(track->node), parent, new);
+ rb_insert_color(&(track->node), &alloc_users);
+
+ spin_unlock(&alloc_users_lock);
+}
+
+/* Remove user allocation tracking, return NULL if allocation untracked */
+static struct user_struct *remove_user_alloc(void *addr, unsigned long *pages)
+{
+ struct rb_node *cur_node = alloc_users.rb_node;
+ unsigned long addrl = (unsigned long) addr;
+ struct mod_alloc_user *cur_alloc_user = NULL;
+ struct user_struct *user;
+
+ spin_lock(&alloc_users_lock);
+ while (cur_node) {
+ cur_alloc_user =
+ rb_entry(cur_node, struct mod_alloc_user, node);
+ if (cur_alloc_user->addr > addrl)
+ cur_node = cur_node->rb_left;
+ else if (cur_alloc_user->addr < addrl)
+ cur_node = cur_node->rb_right;
+ else
+ goto found;
+ }
+ spin_unlock(&alloc_users_lock);
+
+ return NULL;
+found:
+ rb_erase(&cur_alloc_user->node, &alloc_users);
+ spin_unlock(&alloc_users_lock);
+
+ user = find_user(cur_alloc_user->uid);
+ *pages = cur_alloc_user->pages;
+ kfree(cur_alloc_user);
+
+ return user;
+}
+
+int check_inc_mod_rlimit(unsigned long size)
+{
+ struct user_struct *user = get_current_user();
+ unsigned long modspace_pages = rlimit(RLIMIT_MODSPACE) >> PAGE_SHIFT;
+ unsigned long cur_pages = atomic_long_read(&user->module_vm);
+ unsigned long new_pages = get_mod_page_cnt(size);
+
+ if (rlimit(RLIMIT_MODSPACE) != RLIM_INFINITY
+ && cur_pages + new_pages > modspace_pages) {
+ free_uid(user);
+ return 1;
+ }
+
+ atomic_long_add(new_pages, &user->module_vm);
+
+ if (atomic_long_read(&user->module_vm) > modspace_pages) {
+ atomic_long_sub(new_pages, &user->module_vm);
+ free_uid(user);
+ return 1;
+ }
+
+ free_uid(user);
+ return 0;
+}
+
+void dec_mod_rlimit(void *addr)
+{
+ unsigned long pages;
+ struct user_struct *user = remove_user_alloc(addr, &pages);
+
+ if (!user)
+ return;
+
+ atomic_long_sub(pages, &user->module_vm);
+ free_uid(user);
+}
+
void __weak module_memfree(void *module_region)
{
vfree(module_region);
+ dec_mod_rlimit(module_region);
}

void __weak module_arch_cleanup(struct module *mod)
@@ -2730,7 +2860,16 @@ static void dynamic_debug_remove(struct module *mod, struct _ddebug *debug)

void * __weak module_alloc(unsigned long size)
{
- return vmalloc_exec(size);
+ void *p;
+
+ if (check_inc_mod_rlimit(size))
+ return NULL;
+
+ p = vmalloc_exec(size);
+
+ update_mod_rlimit(p, size);
+
+ return p;
}

#ifdef CONFIG_DEBUG_KMEMLEAK
--
2.17.1