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Date: Fri, 25 Aug 2017 12:41:27 +0300 From: Elena Reshetova <elena.reshetova@...el.com> To: linux-kernel@...r.kernel.org Cc: linux-fsdevel@...r.kernel.org, peterz@...radead.org, gregkh@...uxfoundation.org, viro@...iv.linux.org.uk, tj@...nel.org, mingo@...hat.com, hannes@...xchg.org, lizefan@...wei.com, acme@...nel.org, alexander.shishkin@...ux.intel.com, eparis@...hat.com, akpm@...ux-foundation.org, arnd@...db.de, luto@...nel.org, keescook@...omium.org, tglx@...utronix.de, dvhart@...radead.org, ebiederm@...ssion.com, Elena Reshetova <elena.reshetova@...el.com> Subject: [PATCH 10/15] uprobes: convert uprobe.ref to refcount_t atomic_t variables are currently used to implement reference counters with the following properties: - counter is initialized to 1 using atomic_set() - a resource is freed upon counter reaching zero - once counter reaches zero, its further increments aren't allowed - counter schema uses basic atomic operations (set, inc, inc_not_zero, dec_and_test, etc.) Such atomic variables should be converted to a newly provided refcount_t type and API that prevents accidental counter overflows and underflows. This is important since overflows and underflows can lead to use-after-free situation and be exploitable. The variable uprobe.ref is used as pure reference counter. Convert it to refcount_t and fix up the operations. Suggested-by: Kees Cook <keescook@...omium.org> Reviewed-by: David Windsor <dwindsor@...il.com> Reviewed-by: Hans Liljestrand <ishkamiel@...il.com> Signed-off-by: Elena Reshetova <elena.reshetova@...el.com> --- kernel/events/uprobes.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index 456596d..ca093957 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -66,7 +66,7 @@ static struct percpu_rw_semaphore dup_mmap_sem; struct uprobe { struct rb_node rb_node; /* node in the rb tree */ - atomic_t ref; + refcount_t ref; struct rw_semaphore register_rwsem; struct rw_semaphore consumer_rwsem; struct list_head pending_list; @@ -371,13 +371,13 @@ set_orig_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long v static struct uprobe *get_uprobe(struct uprobe *uprobe) { - atomic_inc(&uprobe->ref); + refcount_inc(&uprobe->ref); return uprobe; } static void put_uprobe(struct uprobe *uprobe) { - if (atomic_dec_and_test(&uprobe->ref)) + if (refcount_dec_and_test(&uprobe->ref)) kfree(uprobe); } @@ -459,7 +459,7 @@ static struct uprobe *__insert_uprobe(struct uprobe *uprobe) rb_link_node(&uprobe->rb_node, parent, p); rb_insert_color(&uprobe->rb_node, &uprobes_tree); /* get access + creation ref */ - atomic_set(&uprobe->ref, 2); + refcount_set(&uprobe->ref, 2); return u; } -- 2.7.4
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