register_shrinker allocates dynamic memory and thus is susceptible to failures
under low-memory situation. Currently,get_userns ignores the return value of
register_shrinker, potentially exposing not fully initialised object. This
can lead to a NULL-ptr deref everytime shrinker->nr_deferred is referenced.
Fix this by failing to register the filesystem in case there is not enough
memory to fully construct the shrinker object.
Signed-off-by: Nikolay Borisov <nborisov@xxxxxxxx>
---
fs/super.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/fs/super.c b/fs/super.c
index b8b6a086c03b..964b18447c92 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -518,7 +518,19 @@ struct super_block *sget_userns(struct file_system_type *type,
hlist_add_head(&s->s_instances, &type->fs_supers);
spin_unlock(&sb_lock);
get_filesystem(type);
- register_shrinker(&s->s_shrink);
+ err = register_shrinker(&s->s_shrink);
+ if (err) {
+ spin_lock(&sb_lock);
+ list_del(&s->s_list);
+ hlist_del(&s->s_instances);
+ spin_unlock(&sb_lock);
+
+ up_write(&s->s_umount);
+ destroy_super(s);
+ put_filesystem(type);
+ return ERR_PTR(err);
+ }
+
return s;
}
--
2.7.4
