Author: mjg
Date: Sun Feb 16 03:14:55 2020
New Revision: 357989
URL: https://svnweb.freebsd.org/changeset/base/357989
Log:
refcount: add missing release fence to refcount_release_if_gt
The CPU succeeding in releasing the not last reference can still have pending
stores to the object protected by the affected counter. This opens a time
window where another CPU can release the last reference and free the object,
resulting in use-after-free. On top of that this prevents the compiler from
generating more accesses to the object regardless of how
atomic_fcmpset_rel_int
is implemented (of course as long as it provides the release semantic).
Reviewed by: markj
Modified:
head/sys/sys/refcount.h
Modified: head/sys/sys/refcount.h
==============================================================================
--- head/sys/sys/refcount.h Sun Feb 16 01:07:19 2020 (r357988)
+++ head/sys/sys/refcount.h Sun Feb 16 03:14:55 2020 (r357989)
@@ -198,7 +198,7 @@ refcount_release_if_gt(volatile u_int *count, u_int n)
return (false);
if (__predict_false(REFCOUNT_SATURATED(old)))
return (true);
- if (atomic_fcmpset_int(count, &old, old - 1))
+ if (atomic_fcmpset_rel_int(count, &old, old - 1))
return (true);
}
}
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