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authorElena Reshetova <elena.reshetova@intel.com>2019-01-18 14:27:30 +0200
committerIngo Molnar <mingo@kernel.org>2019-02-04 08:53:56 +0100
commitf0b89d3958d73cd0785ec381f0ddf8efb6f183d8 (patch)
tree4592c3e286b545412053241a5e5f37941e1d9d7a /kernel/fork.c
parentec1d281923cf81cc660343d0cb8ffc837ffb991d (diff)
sched/core: Convert task_struct.stack_refcount 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 task_struct.stack_refcount is used as pure reference counter. Convert it to refcount_t and fix up the operations. ** Important note for maintainers: Some functions from refcount_t API defined in lib/refcount.c have different memory ordering guarantees than their atomic counterparts. The full comparison can be seen in https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon in state to be merged to the documentation tree. Normally the differences should not matter since refcount_t provides enough guarantees to satisfy the refcounting use cases, but in some rare cases it might matter. Please double check that you don't have some undocumented memory guarantees for this variable usage. For the task_struct.stack_refcount it might make a difference in following places: - try_get_task_stack(): increment in refcount_inc_not_zero() only guarantees control dependency on success vs. fully ordered atomic counterpart - put_task_stack(): decrement in refcount_dec_and_test() only provides RELEASE ordering and control dependency on success vs. fully ordered atomic counterpart Suggested-by: Kees Cook <keescook@chromium.org> Signed-off-by: Elena Reshetova <elena.reshetova@intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: David Windsor <dwindsor@gmail.com> Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com> Reviewed-by: Andrea Parri <andrea.parri@amarulasolutions.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: akpm@linux-foundation.org Cc: viro@zeniv.linux.org.uk Link: https://lkml.kernel.org/r/1547814450-18902-6-git-send-email-elena.reshetova@intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/fork.c')
-rw-r--r--kernel/fork.c6
1 files changed, 3 insertions, 3 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index 3f7e192e29f2..77059b211608 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -429,7 +429,7 @@ static void release_task_stack(struct task_struct *tsk)
#ifdef CONFIG_THREAD_INFO_IN_TASK
void put_task_stack(struct task_struct *tsk)
{
- if (atomic_dec_and_test(&tsk->stack_refcount))
+ if (refcount_dec_and_test(&tsk->stack_refcount))
release_task_stack(tsk);
}
#endif
@@ -447,7 +447,7 @@ void free_task(struct task_struct *tsk)
* If the task had a separate stack allocation, it should be gone
* by now.
*/
- WARN_ON_ONCE(atomic_read(&tsk->stack_refcount) != 0);
+ WARN_ON_ONCE(refcount_read(&tsk->stack_refcount) != 0);
#endif
rt_mutex_debug_task_free(tsk);
ftrace_graph_exit_task(tsk);
@@ -867,7 +867,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
tsk->stack_vm_area = stack_vm_area;
#endif
#ifdef CONFIG_THREAD_INFO_IN_TASK
- atomic_set(&tsk->stack_refcount, 1);
+ refcount_set(&tsk->stack_refcount, 1);
#endif
if (err)