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Avoid taking a write lock in RAND_get_rand_method()

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The function RAND_get_rand_method() is called every time RAND_bytes() or
RAND_priv_bytes() is called. We were obtaining a write lock in order to
find the default random method - even though we rarely write. We change
this to a read lock and only fallback to a write lock if we need to.

Partial fix for #20286

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20929)
This commit is contained in:
Matt Caswell 2023-05-10 14:44:17 +01:00
parent 36424806d6
commit 7f2c22c1b9
1 changed files with 7 additions and 0 deletions
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7
crypto/rand/rand_lib.c
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@ -189,6 +189,13 @@ const RAND_METHOD *RAND_get_rand_method(void)
if (!RUN_ONCE(&rand_init, do_rand_init))
return NULL;
if (!CRYPTO_THREAD_read_lock(rand_meth_lock))
return NULL;
tmp_meth = default_RAND_meth;
CRYPTO_THREAD_unlock(rand_meth_lock);
if (tmp_meth != NULL)
return tmp_meth;
if (!CRYPTO_THREAD_write_lock(rand_meth_lock))
return NULL;
if (default_RAND_meth == NULL) {