x86/power/hibernate_64: 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 by switching to
shash directly and allocating the descriptor in heap memory (which should
be fine: the tfm has already been allocated there too).

Link: https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com # [1]
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 21 insertions, 15 deletions

diff --git a/arch/x86/power/hibernate_64.c b/arch/x86/power/hibernate_64.c
index 67ccf64c8bd8..f8e3b668d20b 100644
--- a/arch/x86/power/hibernate_64.c
+++ b/arch/x86/power/hibernate_64.c
@@ -233,29 +233,35 @@ struct restore_data_record {
  */
 static int get_e820_md5(struct e820_table *table, void *buf)
 {
-        struct scatterlist sg;
-        struct crypto_ahash *tfm;
+        struct crypto_shash *tfm;
+        struct shash_desc *desc;
         int size;
         int ret = 0;
 
-        tfm = crypto_alloc_ahash("md5", 0, CRYPTO_ALG_ASYNC);
+        tfm = crypto_alloc_shash("md5", 0, 0);
         if (IS_ERR(tfm))
                 return -ENOMEM;
 
-        {
-                AHASH_REQUEST_ON_STACK(req, tfm);
-                size = offsetof(struct e820_table, entries) + sizeof(struct e820_entry) * table->nr_entries;
-                ahash_request_set_tfm(req, tfm);
-                sg_init_one(&sg, (u8 *)table, size);
-                ahash_request_set_callback(req, 0, NULL, NULL);
-                ahash_request_set_crypt(req, &sg, buf, size);
-
-                if (crypto_ahash_digest(req))
-                        ret = -EINVAL;
-                ahash_request_zero(req);
+        desc = kmalloc(sizeof(struct shash_desc) + crypto_shash_descsize(tfm),
+                       GFP_KERNEL);
+        if (!desc) {
+                ret = -ENOMEM;
+                goto free_tfm;
         }
-        crypto_free_ahash(tfm);
 
+        desc->tfm = tfm;
+        desc->flags = 0;
+
+        size = offsetof(struct e820_table, entries) +
+                sizeof(struct e820_entry) * table->nr_entries;
+
+        if (crypto_shash_digest(desc, (u8 *)table, size, buf))
+                ret = -EINVAL;
+
+        kzfree(desc);
+
+free_tfm:
+        crypto_free_shash(tfm);
         return ret;
 }