A "find" operation on a stack can end up sorting the underlying stack. In
this case it is necessary to use a "write" lock to synchronise access to
the stack across multiple threads.
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17018)
#endif
tmpl.name = (char *)name;
- if (!CRYPTO_THREAD_read_lock(store->lock))
+ /*
+ * A "find" operation can sort the stack, and therefore a write lock is
+ * required.
+ */
+ if (!CRYPTO_THREAD_write_lock(store->lock))
return NULL;
if ((i = sk_OSSL_PROVIDER_find(store->providers, &tmpl)) != -1)
prov = sk_OSSL_PROVIDER_value(store->providers, i);
B<sk_I<TYPE>_find>() returns the index of a matching element or B<-1> if there
is no match. Note that, in this case the comparison function will usually
compare the values pointed to rather than the pointers themselves and
-the order of elements in I<sk> can change.
+the order of elements in I<sk> can change. Note that because the stack may be
+sorted as the result of a B<sk_I<TYPE>_find>() call, if a lock is being used to
+synchronise access to the stack across multiple threads, then that lock must be
+a "write" lock.
B<sk_I<TYPE>_find_ex>() operates like B<sk_I<TYPE>_find>() except when a
comparison function has been specified and no matching element is found.