fscrypto: don't use on-stack buffer for filename encryption

With the new (in 4.9) option to use a virtually-mapped stack
(CONFIG_VMAP_STACK), stack buffers cannot be used as input/output for
the scatterlist crypto API because they may not be directly mappable to
struct page.  For short filenames, fname_encrypt() was encrypting a
stack buffer holding the padded filename.  Fix it by encrypting the
filename in-place in the output buffer, thereby making the temporary
buffer unnecessary.

This bug could most easily be observed in a CONFIG_DEBUG_SG kernel
because this allowed the BUG in sg_set_buf() to be triggered.

Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
index 9a28133ac3b848fc04fdab2e5a91b9e671820f56..9b774f4b50c89e0b4c8e6c26b3eae1595f4dc62f 100644 (file)
--- a/fs/crypto/fname.c
+++ b/fs/crypto/fname.c
@@ -39,65 +39,54 @@ static void fname_crypt_complete(struct crypto_async_request *req, int res)
 static int fname_encrypt(struct inode *inode,
                        const struct qstr *iname, struct fscrypt_str *oname)
 {
-       u32 ciphertext_len;
        struct skcipher_request *req = NULL;
        DECLARE_FS_COMPLETION_RESULT(ecr);
        struct fscrypt_info *ci = inode->i_crypt_info;
        struct crypto_skcipher *tfm = ci->ci_ctfm;
        int res = 0;
        char iv[FS_CRYPTO_BLOCK_SIZE];
-       struct scatterlist src_sg, dst_sg;
+       struct scatterlist sg;
        int padding = 4 << (ci->ci_flags & FS_POLICY_FLAGS_PAD_MASK);
-       char *workbuf, buf[32], *alloc_buf = NULL;
-       unsigned lim;
+       unsigned int lim;
+       unsigned int cryptlen;
 
        lim = inode->i_sb->s_cop->max_namelen(inode);
        if (iname->len <= 0 || iname->len > lim)
                return -EIO;
 
-       ciphertext_len = max(iname->len, (u32)FS_CRYPTO_BLOCK_SIZE);
-       ciphertext_len = round_up(ciphertext_len, padding);
-       ciphertext_len = min(ciphertext_len, lim);
+       /*
+        * Copy the filename to the output buffer for encrypting in-place and
+        * pad it with the needed number of NUL bytes.
+        */
+       cryptlen = max_t(unsigned int, iname->len, FS_CRYPTO_BLOCK_SIZE);
+       cryptlen = round_up(cryptlen, padding);
+       cryptlen = min(cryptlen, lim);
+       memcpy(oname->name, iname->name, iname->len);
+       memset(oname->name + iname->len, 0, cryptlen - iname->len);
 
-       if (ciphertext_len <= sizeof(buf)) {
-               workbuf = buf;
-       } else {
-               alloc_buf = kmalloc(ciphertext_len, GFP_NOFS);
-               if (!alloc_buf)
-                       return -ENOMEM;
-               workbuf = alloc_buf;
-       }
+       /* Initialize the IV */
+       memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);
 
-       /* Allocate request */
+       /* Set up the encryption request */
        req = skcipher_request_alloc(tfm, GFP_NOFS);
        if (!req) {
                printk_ratelimited(KERN_ERR
-                       "%s: crypto_request_alloc() failed\n", __func__);
-               kfree(alloc_buf);
+                       "%s: skcipher_request_alloc() failed\n", __func__);
                return -ENOMEM;
        }
        skcipher_request_set_callback(req,
                        CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
                        fname_crypt_complete, &ecr);
+       sg_init_one(&sg, oname->name, cryptlen);
+       skcipher_request_set_crypt(req, &sg, &sg, cryptlen, iv);
 
-       /* Copy the input */
-       memcpy(workbuf, iname->name, iname->len);
-       if (iname->len < ciphertext_len)
-               memset(workbuf + iname->len, 0, ciphertext_len - iname->len);
-
-       /* Initialize IV */
-       memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);
-
-       /* Create encryption request */
-       sg_init_one(&src_sg, workbuf, ciphertext_len);
-       sg_init_one(&dst_sg, oname->name, ciphertext_len);
-       skcipher_request_set_crypt(req, &src_sg, &dst_sg, ciphertext_len, iv);
+       /* Do the encryption */
        res = crypto_skcipher_encrypt(req);
        if (res == -EINPROGRESS || res == -EBUSY) {
+               /* Request is being completed asynchronously; wait for it */
                wait_for_completion(&ecr.completion);
                res = ecr.res;
        }
-       kfree(alloc_buf);
        skcipher_request_free(req);
        if (res < 0) {
                printk_ratelimited(KERN_ERR
@@ -105,7 +94,7 @@ static int fname_encrypt(struct inode *inode,
                return res;
        }
 
-       oname->len = ciphertext_len;
+       oname->len = cryptlen;
        return 0;
 }