KEYS: Use individual pages in big_key for crypto buffers

kmalloc() can't always allocate large enough buffers for big_key to use for
crypto (1MB + some metadata) so we cannot use that to allocate the buffer.
Further, vmalloc'd pages can't be passed to sg_init_one() and the aead
crypto accessors cannot be called progressively and must be passed all the
data in one go (which means we can't pass the data in one block at a time).

Fix this by allocating the buffer pages individually and passing them
through a multientry scatterlist to the crypto layer.  This has the bonus
advantage that we don't have to allocate a contiguous series of pages.

We then vmap() the page list and pass that through to the VFS read/write
routines.

This can trigger a warning:

	WARNING: CPU: 0 PID: 60912 at mm/page_alloc.c:3883 __alloc_pages_nodemask+0xb7c/0x15f8
	([<00000000002acbb6>] __alloc_pages_nodemask+0x1ee/0x15f8)
	 [<00000000002dd356>] kmalloc_order+0x46/0x90
	 [<00000000002dd3e0>] kmalloc_order_trace+0x40/0x1f8
	 [<0000000000326a10>] __kmalloc+0x430/0x4c0
	 [<00000000004343e4>] big_key_preparse+0x7c/0x210
	 [<000000000042c040>] key_create_or_update+0x128/0x420
	 [<000000000042e52c>] SyS_add_key+0x124/0x220
	 [<00000000007bba2c>] system_call+0xc4/0x2b0

from the keyctl/padd/useradd test of the keyutils testsuite on s390x.

Note that it might be better to shovel data through in page-sized lumps
instead as there's no particular need to use a monolithic buffer unless the
kernel itself wants to access the data.

Fixes: 13100a72f40f ("Security: Keys: Big keys stored encrypted")
Reported-by: Paul Bunyan <pbunyan@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Kirill Marinushkin <k.marinushkin@gmail.com>

1 files changed, 87 insertions, 23 deletions

diff --git a/security/keys/big_key.c b/security/keys/big_key.c
index 929e14978c42..fa728f662a6f 100644
--- a/security/keys/big_key.c
+++ b/security/keys/big_key.c
@@ -22,6 +22,13 @@
 #include <keys/big_key-type.h>
 #include <crypto/aead.h>
 
+struct big_key_buf {
+        unsigned int            nr_pages;
+        void                    *virt;
+        struct scatterlist      *sg;
+        struct page             *pages[];
+};
+
 /*
  * Layout of key payload words.
  */
@@ -91,10 +98,9 @@ static DEFINE_MUTEX(big_key_aead_lock);
 /*
  * Encrypt/decrypt big_key data
  */
-static int big_key_crypt(enum big_key_op op, u8 *data, size_t datalen, u8 *key)
+static int big_key_crypt(enum big_key_op op, struct big_key_buf *buf, size_t datalen, u8 *key)
 {
         int ret;
-        struct scatterlist sgio;
         struct aead_request *aead_req;
         /* We always use a zero nonce. The reason we can get away with this is
          * because we're using a different randomly generated key for every
@@ -109,8 +115,7 @@ static int big_key_crypt(enum big_key_op op, u8 *data, size_t datalen, u8 *key)
                 return -ENOMEM;
 
         memset(zero_nonce, 0, sizeof(zero_nonce));
-        sg_init_one(&sgio, data, datalen + (op == BIG_KEY_ENC ? ENC_AUTHTAG_SIZE : 0));
-        aead_request_set_crypt(aead_req, &sgio, &sgio, datalen, 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);
 
@@ -130,21 +135,81 @@ error:
 }
 
 /*
+ * Free up the buffer.
+ */
+static void big_key_free_buffer(struct big_key_buf *buf)
+{
+        unsigned int i;
+
+        if (buf->virt) {
+                memset(buf->virt, 0, buf->nr_pages * PAGE_SIZE);
+                vunmap(buf->virt);
+        }
+
+        for (i = 0; i < buf->nr_pages; i++)
+                if (buf->pages[i])
+                        __free_page(buf->pages[i]);
+
+        kfree(buf);
+}
+
+/*
+ * Allocate a buffer consisting of a set of pages with a virtual mapping
+ * applied over them.
+ */
+static void *big_key_alloc_buffer(size_t len)
+{
+        struct big_key_buf *buf;
+        unsigned int npg = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
+        unsigned int i, l;
+
+        buf = kzalloc(sizeof(struct big_key_buf) +
+                      sizeof(struct page) * npg +
+                      sizeof(struct scatterlist) * npg,
+                      GFP_KERNEL);
+        if (!buf)
+                return NULL;
+
+        buf->nr_pages = npg;
+        buf->sg = (void *)(buf->pages + npg);
+        sg_init_table(buf->sg, npg);
+
+        for (i = 0; i < buf->nr_pages; i++) {
+                buf->pages[i] = alloc_page(GFP_KERNEL);
+                if (!buf->pages[i])
+                        goto nomem;
+
+                l = min_t(size_t, len, PAGE_SIZE);
+                sg_set_page(&buf->sg[i], buf->pages[i], l, 0);
+                len -= l;
+        }
+
+        buf->virt = vmap(buf->pages, buf->nr_pages, VM_MAP, PAGE_KERNEL);
+        if (!buf->virt)
+                goto nomem;
+
+        return buf;
+
+nomem:
+        big_key_free_buffer(buf);
+        return NULL;
+}
+
+/*
  * Preparse a big key
  */
 int big_key_preparse(struct key_preparsed_payload *prep)
 {
+        struct big_key_buf *buf;
         struct path *path = (struct path *)&prep->payload.data[big_key_path];
         struct file *file;
         u8 *enckey;
-        u8 *data = NULL;
         ssize_t written;
-        size_t datalen = prep->datalen;
+        size_t datalen = prep->datalen, enclen = datalen + ENC_AUTHTAG_SIZE;
         int ret;
 
-        ret = -EINVAL;
         if (datalen <= 0 || datalen > 1024 * 1024 || !prep->data)
-                goto error;
+                return -EINVAL;
 
         /* Set an arbitrary quota */
         prep->quotalen = 16;
@@ -157,13 +222,12 @@ int big_key_preparse(struct key_preparsed_payload *prep)
                  *
                  * File content is stored encrypted with randomly generated key.
                  */
-                size_t enclen = datalen + ENC_AUTHTAG_SIZE;
                 loff_t pos = 0;
 
-                data = kmalloc(enclen, GFP_KERNEL);
-                if (!data)
+                buf = big_key_alloc_buffer(enclen);
+                if (!buf)
                         return -ENOMEM;
-                memcpy(data, prep->data, datalen);
+                memcpy(buf->virt, prep->data, datalen);
 
                 /* generate random key */
                 enckey = kmalloc(ENC_KEY_SIZE, GFP_KERNEL);
@@ -176,7 +240,7 @@ int big_key_preparse(struct key_preparsed_payload *prep)
                         goto err_enckey;
 
                 /* encrypt aligned data */
-                ret = big_key_crypt(BIG_KEY_ENC, data, datalen, enckey);
+                ret = big_key_crypt(BIG_KEY_ENC, buf, datalen, enckey);
                 if (ret)
                         goto err_enckey;
 
@@ -187,7 +251,7 @@ int big_key_preparse(struct key_preparsed_payload *prep)
                         goto err_enckey;
                 }
 
-                written = kernel_write(file, data, enclen, &pos);
+                written = kernel_write(file, buf->virt, enclen, &pos);
                 if (written != enclen) {
                         ret = written;
                         if (written >= 0)
@@ -202,7 +266,7 @@ int big_key_preparse(struct key_preparsed_payload *prep)
                 *path = file->f_path;
                 path_get(path);
                 fput(file);
-                kzfree(data);
+                big_key_free_buffer(buf);
         } else {
                 /* Just store the data in a buffer */
                 void *data = kmalloc(datalen, GFP_KERNEL);
@@ -220,7 +284,7 @@ err_fput:
 err_enckey:
         kzfree(enckey);
 error:
-        kzfree(data);
+        big_key_free_buffer(buf);
         return ret;
 }
 
@@ -298,15 +362,15 @@ long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
                 return datalen;
 
         if (datalen > BIG_KEY_FILE_THRESHOLD) {
+                struct big_key_buf *buf;
                 struct path *path = (struct path *)&key->payload.data[big_key_path];
                 struct file *file;
-                u8 *data;
                 u8 *enckey = (u8 *)key->payload.data[big_key_data];
                 size_t enclen = datalen + ENC_AUTHTAG_SIZE;
                 loff_t pos = 0;
 
-                data = kmalloc(enclen, GFP_KERNEL);
-                if (!data)
+                buf = big_key_alloc_buffer(enclen);
+                if (!buf)
                         return -ENOMEM;
 
                 file = dentry_open(path, O_RDONLY, current_cred());
@@ -316,26 +380,26 @@ long big_key_read(const struct key *key, char __user *buffer, size_t buflen)
                 }
 
                 /* read file to kernel and decrypt */
-                ret = kernel_read(file, data, enclen, &pos);
+                ret = kernel_read(file, buf->virt, enclen, &pos);
                 if (ret >= 0 && ret != enclen) {
                         ret = -EIO;
                         goto err_fput;
                 }
 
-                ret = big_key_crypt(BIG_KEY_DEC, data, enclen, enckey);
+                ret = big_key_crypt(BIG_KEY_DEC, buf, enclen, enckey);
                 if (ret)
                         goto err_fput;
 
                 ret = datalen;
 
                 /* copy decrypted data to user */
-                if (copy_to_user(buffer, data, datalen) != 0)
+                if (copy_to_user(buffer, buf->virt, datalen) != 0)
                         ret = -EFAULT;
 
 err_fput:
                 fput(file);
 error:
-                kzfree(data);
+                big_key_free_buffer(buf);
         } else {
                 ret = datalen;
                 if (copy_to_user(buffer, key->payload.data[big_key_data],