KEYS: fix refcount_inc() on zero
If a key's refcount is dropped to zero between key_lookup() peeking at the refcount and subsequently attempting to increment it, refcount_inc() will see a zero refcount. Here, refcount_inc() will WARN_ONCE(), and will *not* increment the refcount, which will remain zero. Once key_lookup() drops key_serial_lock, it is possible for the key to be freed behind our back. This patch uses refcount_inc_not_zero() to perform the peek and increment atomically. Fixes: fff292914d3a2f1e ("security, keys: convert key.usage from atomic_t to refcount_t") Signed-off-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: David Howells <dhowells@redhat.com> Cc: David Windsor <dwindsor@gmail.com> Cc: Elena Reshetova <elena.reshetova@intel.com> Cc: Hans Liljestrand <ishkamiel@gmail.com> Cc: James Morris <james.l.morris@oracle.com> Cc: Kees Cook <keescook@chromium.org> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: James Morris <james.l.morris@oracle.com>
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@ -660,14 +660,11 @@ not_found:
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goto error;
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found:
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/* pretend it doesn't exist if it is awaiting deletion */
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if (refcount_read(&key->usage) == 0)
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goto not_found;
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/* this races with key_put(), but that doesn't matter since key_put()
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* doesn't actually change the key
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/* A key is allowed to be looked up only if someone still owns a
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* reference to it - otherwise it's awaiting the gc.
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*/
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__key_get(key);
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if (!refcount_inc_not_zero(&key->usage))
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goto not_found;
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error:
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spin_unlock(&key_serial_lock);
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