Correctly free EVP_MD_CTX in OpenSSL #501
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soter_sign_ctx_t structures store both EVP_MD_CTX (to keep the digest algorithm used for signatures) and EVP_PKEY_CTX (to keep the key used for signature). The key is actually shared between those structures but EVP_MD_CTX assumes ownership over it, with EVP_MD_CTX_destroy() freeing the key. EVP_PKEY structures are refcounted so sharing the key should be safe... if we make the correct precautions to avoid freeing the key after it has been freed. EVP_PKEY_CTX keeps track of that, but we need to free EVP_MD_CTX first and then proceed to freeing EVP_PKEY_CTX and maybe the key it has been managing. This sleeper bug is presumed to be responsible for occasional segfaults when running JsThemis. Interestingly, the crashes do not reproduce with any other wrapper. Furthermore, BoringSSL code uses correct freeing order since the beginning. "Coincidence? I don't think so".
vixentael
approved these changes
Jul 18, 2019
ignatk
approved these changes
Jul 18, 2019
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Maybe we should consider running tests under some kind of leak detector. |
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we already use valgrind for leak detection |
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soter_sign_ctx_tstructures store both EVP_MD_CTX (to keep the digest algorithm used for signatures) and EVP_PKEY_CTX (to keep the key used for signature). The key is actually shared between those structures but EVP_MD_CTX assumes ownership over it, with EVP_MD_CTX_destroy() freeing the key. EVP_PKEY structures are refcounted so sharing the key should be safe... if we make the correct precautions to avoid freeing the key after it has been freed. EVP_PKEY_CTX keeps track of that, but we need to free EVP_MD_CTX first and then proceed to freeing EVP_PKEY_CTX and maybe the key it has been managing.tl;dr: manual memory management is hard.
This sleeper bug is presumed to be responsible for occasional segfaults when running JsThemis. Interestingly, the crashes do not reproduce with any other wrapper. Furthermore, BoringSSL code uses correct freeing order since the beginning. "Coincidence? I don't think so".