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Date:   Fri, 30 Aug 2019 10:55:39 -0700 (PDT)
From:   Mat Martineau <mathew.j.martineau@linux.intel.com>
To:     Brian Gix <brian.gix@intel.com>
cc:     linux-bluetooth@vger.kernel.org, inga.stotland@intel.com,
        marcel@holtmann.org
Subject: Re: [PATCH BlueZ] mesh: test AEAD at startup to check kernel
 support
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Hi Brian,

There's also l_aead_cipher_is_supported(L_AEAD_CIPHER_AES_CCM), which 
might fail more cleanly on systems with old kernels or that don't have 
AES_CCM configured. I suggest doing that check first and then proceeding 
to the bug check if AES_CCM is available.

Mat


On Fri, 30 Aug 2019, Brian Gix wrote:

> One time test at startup to ensure either kernel version v4.9 or later,
> *or* that required AES-CCM support has been back-ported. If support not
> there, daemon will run without providing D-Bus service or attaching to
> controllers (prevents systemd thrashing).
> ---
> mesh/crypto.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
> mesh/crypto.h |  1 +
> mesh/main.c   |  7 +++++++
> 3 files changed, 59 insertions(+)
>
> diff --git a/mesh/crypto.c b/mesh/crypto.c
> index a6dc7ffe2..27d1a16cc 100644
> --- a/mesh/crypto.c
> +++ b/mesh/crypto.c
> @@ -1130,3 +1130,54 @@ bool mesh_crypto_check_fcs(const uint8_t *packet, uint8_t packet_len,
>
> 	return fcs == 0xcf;
> }
> +
> +/* This function performs a quick-check of ELL and Kernel AEAD encryption.
> + * Some kernel versions before v4.9 have a known AEAD bug. If the system
> + * running this test is using a v4.8 or earlier kernel, a failure here is
> + * likely unless AEAD encryption has been backported.
> + */
> +static const uint8_t crypto_test_result[] = {
> +	0x75, 0x03, 0x7e, 0xe2, 0x89, 0x81, 0xbe, 0x59,
> +	0xbc, 0xe6, 0xdd, 0x23, 0x63, 0x5b, 0x16, 0x61,
> +	0xb7, 0x23, 0x92, 0xd4, 0x86, 0xee, 0x84, 0x29,
> +	0x9a, 0x2a, 0xbf, 0x96
> +};
> +bool mesh_crypto_check_avail()
> +{
> +	void *cipher;
> +	bool result;
> +	uint8_t i;
> +	union {
> +		struct {
> +			uint8_t key[16];
> +			uint8_t aad[16];
> +			uint8_t nonce[13];
> +			uint8_t data[20];
> +			uint8_t mic[8];
> +		} crypto;
> +		uint8_t bytes[0];
> +	} u;
> +	uint8_t out_msg[sizeof(u.crypto.data) + sizeof(u.crypto.mic)];
> +
> +
> +	l_debug("Testing Crypto");
> +	for (i = 0; i < sizeof(u); i++) {
> +		u.bytes[i] = 0x60 + i;
> +	}
> +
> +	cipher = l_aead_cipher_new(L_AEAD_CIPHER_AES_CCM, u.crypto.key,
> +				sizeof(u.crypto.key), sizeof(u.crypto.mic));
> +
> +	result = l_aead_cipher_encrypt(cipher,
> +				u.crypto.data, sizeof(u.crypto.data),
> +				u.crypto.aad, sizeof(u.crypto.aad),
> +				u.crypto.nonce, sizeof(u.crypto.nonce),
> +				out_msg, sizeof(out_msg));
> +
> +	if (result)
> +		result = !memcmp(out_msg, crypto_test_result, sizeof(out_msg));
> +
> +	l_aead_cipher_free(cipher);
> +
> +	return result;
> +}
> diff --git a/mesh/crypto.h b/mesh/crypto.h
> index 1a73bcaa3..e5ce840b4 100644
> --- a/mesh/crypto.h
> +++ b/mesh/crypto.h
> @@ -161,3 +161,4 @@ bool mesh_crypto_check_fcs(const uint8_t *packet, uint8_t packet_len,
> 							uint8_t received_fcs);
> bool mesh_crypto_aes_cmac(const uint8_t key[16], const uint8_t *msg,
> 					size_t msg_len, uint8_t res[16]);
> +bool mesh_crypto_check_avail(void);
> diff --git a/mesh/main.c b/mesh/main.c
> index 262e3da48..273651f97 100644
> --- a/mesh/main.c
> +++ b/mesh/main.c
> @@ -34,6 +34,7 @@
> #include "lib/mgmt.h"
>
> #include "mesh/mesh.h"
> +#include "mesh/crypto.h"
> #include "mesh/dbus.h"
> #include "mesh/mesh-io.h"
>
> @@ -121,6 +122,12 @@ int main(int argc, char *argv[])
>
> 	l_log_set_stderr();
>
> +	if (!mesh_crypto_check_avail()) {
> +		l_error("Mesh Crypto functions unavailable");
> +		status = l_main_run_with_signal(signal_handler, NULL);
> +		goto done;
> +	}
> +
> 	for (;;) {
> 		int opt;
> 		const char *str;
> -- 
> 2.21.0
>
>

--
Mat Martineau
Intel