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Date: Mon, 12 Mar 2018 22:29:06 -0600
From: Tycho Andersen <>
To: David Howells <>
	Tycho Andersen <>,
	James Morris <>,
	"Serge E. Hallyn" <>,
	"Jason A . Donenfeld" <>
Subject: [PATCH 1/2] big key: get rid of stack array allocation

We're interested in getting rid of all of the stack allocated arrays in the
kernel [1]. This patch removes one in keys by switching to malloc/free.
Note that we use kzalloc, to avoid leaking the nonce. I'm not sure this is
really necessary, but extra paranoia seems prudent.

Manually tested using the program from the add_key man page to trigger


Signed-off-by: Tycho Andersen <>
CC: David Howells <>
CC: James Morris <>
CC: "Serge E. Hallyn" <>
CC: Jason A. Donenfeld <>
 security/keys/big_key.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/security/keys/big_key.c b/security/keys/big_key.c
index fa728f662a6f..70f9f785c59d 100644
--- a/security/keys/big_key.c
+++ b/security/keys/big_key.c
@@ -108,13 +108,18 @@ static int big_key_crypt(enum big_key_op op, struct big_key_buf *buf, size_t dat
 	 * an .update function, so there's no chance we'll wind up reusing the
 	 * key to encrypt updated data. Simply put: one key, one encryption.
-	u8 zero_nonce[crypto_aead_ivsize(big_key_aead)];
+	u8 *zero_nonce;
+	zero_nonce = kzalloc(crypto_aead_ivsize(big_key_aead), GFP_KERNEL);
+	if (!zero_nonce)
+		return -ENOMEM;
 	aead_req = aead_request_alloc(big_key_aead, GFP_KERNEL);
-	if (!aead_req)
+	if (!aead_req) {
+		kfree(zero_nonce);
 		return -ENOMEM;
+	}
-	memset(zero_nonce, 0, sizeof(zero_nonce));
 	aead_request_set_crypt(aead_req, buf->sg, buf->sg, datalen, zero_nonce);
 	aead_request_set_callback(aead_req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);
 	aead_request_set_ad(aead_req, 0);
@@ -131,6 +136,7 @@ static int big_key_crypt(enum big_key_op op, struct big_key_buf *buf, size_t dat
+	kzfree(zero_nonce);
 	return ret;

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