refcount_t type and corresponding API should be used instead of atomic_t when the variable is used as a reference counter. This allows to avoid accidental refcounter overflows that might lead to use-after-free situations.
Signed-off-by: Elena Reshetova <[email protected]> Signed-off-by: Hans Liljestrand <[email protected]> Signed-off-by: Kees Cook <[email protected]> Signed-off-by: David Windsor <[email protected]> --- fs/kernfs/dir.c | 12 +++++------- include/linux/kernfs.h | 3 ++- 2 files changed, 7 insertions(+), 8 deletions(-) diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index db5900aaa..2a07de1 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -489,10 +489,8 @@ static void kernfs_drain(struct kernfs_node *kn) */ void kernfs_get(struct kernfs_node *kn) { - if (kn) { - WARN_ON(!atomic_read(&kn->count)); - atomic_inc(&kn->count); - } + if (kn) + refcount_inc(&kn->count); } EXPORT_SYMBOL_GPL(kernfs_get); @@ -507,7 +505,7 @@ void kernfs_put(struct kernfs_node *kn) struct kernfs_node *parent; struct kernfs_root *root; - if (!kn || !atomic_dec_and_test(&kn->count)) + if (!kn || !refcount_dec_and_test(&kn->count)) return; root = kernfs_root(kn); repeat: @@ -538,7 +536,7 @@ void kernfs_put(struct kernfs_node *kn) kn = parent; if (kn) { - if (atomic_dec_and_test(&kn->count)) + if (refcount_dec_and_test(&kn->count)) goto repeat; } else { /* just released the root kn, free @root too */ @@ -635,7 +633,7 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root, goto err_out2; kn->ino = ret; - atomic_set(&kn->count, 1); + refcount_set(&kn->count, 1); atomic_set(&kn->active, KN_DEACTIVATED_BIAS); RB_CLEAR_NODE(&kn->rb); diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h index a9b11b8..baabbaf 100644 --- a/include/linux/kernfs.h +++ b/include/linux/kernfs.h @@ -15,6 +15,7 @@ #include <linux/lockdep.h> #include <linux/rbtree.h> #include <linux/atomic.h> +#include <linux/refcount.h> #include <linux/wait.h> struct file; @@ -105,7 +106,7 @@ struct kernfs_elem_attr { * active reference. */ struct kernfs_node { - atomic_t count; + refcount_t count; atomic_t active; #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lockdep_map dep_map; -- 2.7.4
