ppp: mppe: Remove VLA usage

In the quest to remove all stack VLA usage from the kernel[1], this
removes the discouraged use of AHASH_REQUEST_ON_STACK (and associated
VLA) by switching to shash directly and keeping the associated descriptor
allocated with the regular state on the heap.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ppp/ppp_mppe.c b/drivers/net/ppp/ppp_mppe.c
index 6c7fd98cb00a12afe89a04af55ae40cb16c825f0..a205750b431ba5565df39a3d7d94ac409513fd9e 100644 (file)
--- a/drivers/net/ppp/ppp_mppe.c
+++ b/drivers/net/ppp/ppp_mppe.c
@@ -96,7 +96,7 @@ static inline void sha_pad_init(struct sha_pad *shapad)
  */
 struct ppp_mppe_state {
        struct crypto_skcipher *arc4;
-       struct crypto_ahash *sha1;
+       struct shash_desc *sha1;
        unsigned char *sha1_digest;
        unsigned char master_key[MPPE_MAX_KEY_LEN];
        unsigned char session_key[MPPE_MAX_KEY_LEN];
@@ -136,25 +136,16 @@ struct ppp_mppe_state {
  */
 static void get_new_key_from_sha(struct ppp_mppe_state * state)
 {
-       AHASH_REQUEST_ON_STACK(req, state->sha1);
-       struct scatterlist sg[4];
-       unsigned int nbytes;
-
-       sg_init_table(sg, 4);
-
-       nbytes = setup_sg(&sg[0], state->master_key, state->keylen);
-       nbytes += setup_sg(&sg[1], sha_pad->sha_pad1,
-                          sizeof(sha_pad->sha_pad1));
-       nbytes += setup_sg(&sg[2], state->session_key, state->keylen);
-       nbytes += setup_sg(&sg[3], sha_pad->sha_pad2,
-                          sizeof(sha_pad->sha_pad2));
-
-       ahash_request_set_tfm(req, state->sha1);
-       ahash_request_set_callback(req, 0, NULL, NULL);
-       ahash_request_set_crypt(req, sg, state->sha1_digest, nbytes);
-
-       crypto_ahash_digest(req);
-       ahash_request_zero(req);
+       crypto_shash_init(state->sha1);
+       crypto_shash_update(state->sha1, state->master_key,
+                           state->keylen);
+       crypto_shash_update(state->sha1, sha_pad->sha_pad1,
+                           sizeof(sha_pad->sha_pad1));
+       crypto_shash_update(state->sha1, state->session_key,
+                           state->keylen);
+       crypto_shash_update(state->sha1, sha_pad->sha_pad2,
+                           sizeof(sha_pad->sha_pad2));
+       crypto_shash_final(state->sha1, state->sha1_digest);
 }
 
 /*
@@ -200,6 +191,7 @@ static void mppe_rekey(struct ppp_mppe_state * state, int initial_key)
 static void *mppe_alloc(unsigned char *options, int optlen)
 {
        struct ppp_mppe_state *state;
+       struct crypto_shash *shash;
        unsigned int digestsize;
 
        if (optlen != CILEN_MPPE + sizeof(state->master_key) ||
@@ -217,13 +209,21 @@ static void *mppe_alloc(unsigned char *options, int optlen)
                goto out_free;
        }
 
-       state->sha1 = crypto_alloc_ahash("sha1", 0, CRYPTO_ALG_ASYNC);
-       if (IS_ERR(state->sha1)) {
-               state->sha1 = NULL;
+       shash = crypto_alloc_shash("sha1", 0, 0);
+       if (IS_ERR(shash))
+               goto out_free;
+
+       state->sha1 = kmalloc(sizeof(*state->sha1) +
+                                    crypto_shash_descsize(shash),
+                             GFP_KERNEL);
+       if (!state->sha1) {
+               crypto_free_shash(shash);
                goto out_free;
        }
+       state->sha1->tfm = shash;
+       state->sha1->flags = 0;
 
-       digestsize = crypto_ahash_digestsize(state->sha1);
+       digestsize = crypto_shash_digestsize(shash);
        if (digestsize < MPPE_MAX_KEY_LEN)
                goto out_free;
 
@@ -246,7 +246,10 @@ static void *mppe_alloc(unsigned char *options, int optlen)
 
 out_free:
        kfree(state->sha1_digest);
-       crypto_free_ahash(state->sha1);
+       if (state->sha1) {
+               crypto_free_shash(state->sha1->tfm);
+               kzfree(state->sha1);
+       }
        crypto_free_skcipher(state->arc4);
        kfree(state);
 out:
@@ -261,7 +264,8 @@ static void mppe_free(void *arg)
        struct ppp_mppe_state *state = (struct ppp_mppe_state *) arg;
        if (state) {
                kfree(state->sha1_digest);
-               crypto_free_ahash(state->sha1);
+               crypto_free_shash(state->sha1->tfm);
+               kzfree(state->sha1);
                crypto_free_skcipher(state->arc4);
                kfree(state);
        }