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>

1 files changed, 30 insertions, 26 deletions

diff --git a/drivers/net/ppp/ppp_mppe.c b/drivers/net/ppp/ppp_mppe.c
index 6c7fd98cb00a..a205750b431b 100644
--- 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);
         }