[PATCH 6/6] KEYS: Use individual pages in big_key for crypto buffers
David Howells
dhowells at redhat.com
Thu Feb 22 16:21:09 UTC 2018
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 at redhat.com>
Signed-off-by: David Howells <dhowells at redhat.com>
cc: Kirill Marinushkin <k.marinushkin at gmail.com>
---
security/keys/big_key.c | 110 +++++++++++++++++++++++++++++++++++++----------
1 file changed, 87 insertions(+), 23 deletions(-)
diff --git a/security/keys/big_key.c b/security/keys/big_key.c
index 929e14978c42..4e99e8ba8612 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 @@ static int big_key_crypt(enum big_key_op op, u8 *data, size_t datalen, u8 *key)
}
/*
+ * 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(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 @@ int big_key_preparse(struct key_preparsed_payload *prep)
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],
--
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