[PATCH v2 4/6] Bluetooth: SMP: clear the aes_cmac_key when done

[PATCH v2 4/6] Bluetooth: SMP: clear the aes_cmac_key when done

[Thomas Huth]

From: Thomas Huth <thuth@redhat.com>

Clear the local aes_cmac_key structure via __cleanup() function
when we're done with it to avoid that sensitive data could leak on
the stack.

While we're at it, also clear the tmp[] array here that is populated
with a raw version of the original key and thus would leak the same
information via the stack otherwise.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 net/bluetooth/smp.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index c4470958b0d57..4a32e4f80b48a 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -164,7 +164,7 @@ static inline void swap_buf(const u8 *src, u8 *dst, size_t len)
 static int smp_aes_cmac(const u8 k[16], const u8 *m, size_t len, u8 mac[16])
 {
 	uint8_t tmp[16], mac_msb[16], msg_msb[CMAC_MSG_MAX];
-	struct aes_cmac_key key;
+	struct aes_cmac_key key __cleanup(aes_cmac_zeroize_key);
 	int err;
 
 	if (len > CMAC_MSG_MAX)
@@ -178,6 +178,7 @@ static int smp_aes_cmac(const u8 k[16], const u8 *m, size_t len, u8 mac[16])
 	SMP_DBG("key %16phN", k);
 
 	err = aes_cmac_preparekey(&key, tmp, 16);
+	memzero_explicit(tmp, sizeof(tmp));
 	if (WARN_ON_ONCE(err)) /* Should never happen, as 16 is valid keylen */
 		return err;
 	aes_cmac(&key, msg_msb, len, mac_msb);
-- 
2.55.0