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![Eric Biggers](/assets/img/avatar_default.png)
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>
414 lines
10 KiB
C
414 lines
10 KiB
C
/*
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* This contains functions for filename crypto management
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*
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* Copyright (C) 2015, Google, Inc.
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* Copyright (C) 2015, Motorola Mobility
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*
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* Written by Uday Savagaonkar, 2014.
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* Modified by Jaegeuk Kim, 2015.
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*
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* This has not yet undergone a rigorous security audit.
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*/
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#include <linux/scatterlist.h>
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#include <linux/ratelimit.h>
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#include <linux/fscrypto.h>
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/**
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* fname_crypt_complete() - completion callback for filename crypto
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* @req: The asynchronous cipher request context
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* @res: The result of the cipher operation
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*/
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static void fname_crypt_complete(struct crypto_async_request *req, int res)
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{
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struct fscrypt_completion_result *ecr = req->data;
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if (res == -EINPROGRESS)
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return;
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ecr->res = res;
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complete(&ecr->completion);
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}
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/**
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* fname_encrypt() - encrypt a filename
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*
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* The caller must have allocated sufficient memory for the @oname string.
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*
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* Return: 0 on success, -errno on failure
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*/
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static int fname_encrypt(struct inode *inode,
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const struct qstr *iname, struct fscrypt_str *oname)
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{
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struct skcipher_request *req = NULL;
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DECLARE_FS_COMPLETION_RESULT(ecr);
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struct fscrypt_info *ci = inode->i_crypt_info;
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struct crypto_skcipher *tfm = ci->ci_ctfm;
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int res = 0;
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char iv[FS_CRYPTO_BLOCK_SIZE];
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struct scatterlist sg;
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int padding = 4 << (ci->ci_flags & FS_POLICY_FLAGS_PAD_MASK);
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unsigned int lim;
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unsigned int cryptlen;
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lim = inode->i_sb->s_cop->max_namelen(inode);
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if (iname->len <= 0 || iname->len > lim)
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return -EIO;
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/*
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* Copy the filename to the output buffer for encrypting in-place and
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* pad it with the needed number of NUL bytes.
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*/
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cryptlen = max_t(unsigned int, iname->len, FS_CRYPTO_BLOCK_SIZE);
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cryptlen = round_up(cryptlen, padding);
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cryptlen = min(cryptlen, lim);
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memcpy(oname->name, iname->name, iname->len);
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memset(oname->name + iname->len, 0, cryptlen - iname->len);
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/* Initialize the IV */
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memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);
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/* Set up the encryption request */
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req = skcipher_request_alloc(tfm, GFP_NOFS);
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if (!req) {
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printk_ratelimited(KERN_ERR
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"%s: skcipher_request_alloc() failed\n", __func__);
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return -ENOMEM;
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}
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skcipher_request_set_callback(req,
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CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
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fname_crypt_complete, &ecr);
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sg_init_one(&sg, oname->name, cryptlen);
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skcipher_request_set_crypt(req, &sg, &sg, cryptlen, iv);
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/* Do the encryption */
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res = crypto_skcipher_encrypt(req);
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if (res == -EINPROGRESS || res == -EBUSY) {
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/* Request is being completed asynchronously; wait for it */
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wait_for_completion(&ecr.completion);
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res = ecr.res;
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}
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skcipher_request_free(req);
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if (res < 0) {
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printk_ratelimited(KERN_ERR
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"%s: Error (error code %d)\n", __func__, res);
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return res;
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}
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oname->len = cryptlen;
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return 0;
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}
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/**
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* fname_decrypt() - decrypt a filename
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*
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* The caller must have allocated sufficient memory for the @oname string.
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*
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* Return: 0 on success, -errno on failure
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*/
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static int fname_decrypt(struct inode *inode,
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const struct fscrypt_str *iname,
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struct fscrypt_str *oname)
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{
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struct skcipher_request *req = NULL;
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DECLARE_FS_COMPLETION_RESULT(ecr);
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struct scatterlist src_sg, dst_sg;
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struct fscrypt_info *ci = inode->i_crypt_info;
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struct crypto_skcipher *tfm = ci->ci_ctfm;
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int res = 0;
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char iv[FS_CRYPTO_BLOCK_SIZE];
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unsigned lim;
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lim = inode->i_sb->s_cop->max_namelen(inode);
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if (iname->len <= 0 || iname->len > lim)
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return -EIO;
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/* Allocate request */
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req = skcipher_request_alloc(tfm, GFP_NOFS);
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if (!req) {
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printk_ratelimited(KERN_ERR
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"%s: crypto_request_alloc() failed\n", __func__);
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return -ENOMEM;
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}
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skcipher_request_set_callback(req,
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CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
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fname_crypt_complete, &ecr);
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/* Initialize IV */
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memset(iv, 0, FS_CRYPTO_BLOCK_SIZE);
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/* Create decryption request */
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sg_init_one(&src_sg, iname->name, iname->len);
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sg_init_one(&dst_sg, oname->name, oname->len);
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skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, iv);
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res = crypto_skcipher_decrypt(req);
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if (res == -EINPROGRESS || res == -EBUSY) {
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wait_for_completion(&ecr.completion);
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res = ecr.res;
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}
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skcipher_request_free(req);
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if (res < 0) {
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printk_ratelimited(KERN_ERR
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"%s: Error (error code %d)\n", __func__, res);
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return res;
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}
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oname->len = strnlen(oname->name, iname->len);
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return 0;
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}
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static const char *lookup_table =
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"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
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/**
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* digest_encode() -
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*
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* Encodes the input digest using characters from the set [a-zA-Z0-9_+].
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* The encoded string is roughly 4/3 times the size of the input string.
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*/
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static int digest_encode(const char *src, int len, char *dst)
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{
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int i = 0, bits = 0, ac = 0;
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char *cp = dst;
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while (i < len) {
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ac += (((unsigned char) src[i]) << bits);
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bits += 8;
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do {
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*cp++ = lookup_table[ac & 0x3f];
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ac >>= 6;
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bits -= 6;
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} while (bits >= 6);
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i++;
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}
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if (bits)
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*cp++ = lookup_table[ac & 0x3f];
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return cp - dst;
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}
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static int digest_decode(const char *src, int len, char *dst)
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{
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int i = 0, bits = 0, ac = 0;
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const char *p;
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char *cp = dst;
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while (i < len) {
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p = strchr(lookup_table, src[i]);
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if (p == NULL || src[i] == 0)
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return -2;
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ac += (p - lookup_table) << bits;
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bits += 6;
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if (bits >= 8) {
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*cp++ = ac & 0xff;
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ac >>= 8;
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bits -= 8;
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}
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i++;
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}
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if (ac)
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return -1;
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return cp - dst;
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}
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u32 fscrypt_fname_encrypted_size(struct inode *inode, u32 ilen)
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{
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int padding = 32;
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struct fscrypt_info *ci = inode->i_crypt_info;
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if (ci)
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padding = 4 << (ci->ci_flags & FS_POLICY_FLAGS_PAD_MASK);
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ilen = max(ilen, (u32)FS_CRYPTO_BLOCK_SIZE);
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return round_up(ilen, padding);
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}
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EXPORT_SYMBOL(fscrypt_fname_encrypted_size);
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/**
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* fscrypt_fname_crypto_alloc_obuff() -
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*
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* Allocates an output buffer that is sufficient for the crypto operation
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* specified by the context and the direction.
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*/
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int fscrypt_fname_alloc_buffer(struct inode *inode,
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u32 ilen, struct fscrypt_str *crypto_str)
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{
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unsigned int olen = fscrypt_fname_encrypted_size(inode, ilen);
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crypto_str->len = olen;
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if (olen < FS_FNAME_CRYPTO_DIGEST_SIZE * 2)
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olen = FS_FNAME_CRYPTO_DIGEST_SIZE * 2;
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/*
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* Allocated buffer can hold one more character to null-terminate the
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* string
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*/
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crypto_str->name = kmalloc(olen + 1, GFP_NOFS);
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if (!(crypto_str->name))
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return -ENOMEM;
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return 0;
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}
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EXPORT_SYMBOL(fscrypt_fname_alloc_buffer);
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/**
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* fscrypt_fname_crypto_free_buffer() -
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*
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* Frees the buffer allocated for crypto operation.
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*/
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void fscrypt_fname_free_buffer(struct fscrypt_str *crypto_str)
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{
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if (!crypto_str)
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return;
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kfree(crypto_str->name);
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crypto_str->name = NULL;
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}
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EXPORT_SYMBOL(fscrypt_fname_free_buffer);
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/**
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* fscrypt_fname_disk_to_usr() - converts a filename from disk space to user
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* space
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*
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* The caller must have allocated sufficient memory for the @oname string.
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*
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* Return: 0 on success, -errno on failure
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*/
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int fscrypt_fname_disk_to_usr(struct inode *inode,
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u32 hash, u32 minor_hash,
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const struct fscrypt_str *iname,
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struct fscrypt_str *oname)
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{
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const struct qstr qname = FSTR_TO_QSTR(iname);
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char buf[24];
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if (fscrypt_is_dot_dotdot(&qname)) {
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oname->name[0] = '.';
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oname->name[iname->len - 1] = '.';
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oname->len = iname->len;
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return 0;
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}
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if (iname->len < FS_CRYPTO_BLOCK_SIZE)
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return -EUCLEAN;
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if (inode->i_crypt_info)
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return fname_decrypt(inode, iname, oname);
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if (iname->len <= FS_FNAME_CRYPTO_DIGEST_SIZE) {
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oname->len = digest_encode(iname->name, iname->len,
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oname->name);
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return 0;
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}
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if (hash) {
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memcpy(buf, &hash, 4);
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memcpy(buf + 4, &minor_hash, 4);
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} else {
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memset(buf, 0, 8);
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}
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memcpy(buf + 8, iname->name + iname->len - 16, 16);
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oname->name[0] = '_';
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oname->len = 1 + digest_encode(buf, 24, oname->name + 1);
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return 0;
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}
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EXPORT_SYMBOL(fscrypt_fname_disk_to_usr);
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/**
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* fscrypt_fname_usr_to_disk() - converts a filename from user space to disk
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* space
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*
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* The caller must have allocated sufficient memory for the @oname string.
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*
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* Return: 0 on success, -errno on failure
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*/
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int fscrypt_fname_usr_to_disk(struct inode *inode,
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const struct qstr *iname,
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struct fscrypt_str *oname)
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{
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if (fscrypt_is_dot_dotdot(iname)) {
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oname->name[0] = '.';
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oname->name[iname->len - 1] = '.';
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oname->len = iname->len;
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return 0;
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}
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if (inode->i_crypt_info)
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return fname_encrypt(inode, iname, oname);
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/*
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* Without a proper key, a user is not allowed to modify the filenames
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* in a directory. Consequently, a user space name cannot be mapped to
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* a disk-space name
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*/
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return -EACCES;
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}
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EXPORT_SYMBOL(fscrypt_fname_usr_to_disk);
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int fscrypt_setup_filename(struct inode *dir, const struct qstr *iname,
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int lookup, struct fscrypt_name *fname)
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{
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int ret = 0, bigname = 0;
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memset(fname, 0, sizeof(struct fscrypt_name));
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fname->usr_fname = iname;
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if (!dir->i_sb->s_cop->is_encrypted(dir) ||
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fscrypt_is_dot_dotdot(iname)) {
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fname->disk_name.name = (unsigned char *)iname->name;
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fname->disk_name.len = iname->len;
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return 0;
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}
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ret = get_crypt_info(dir);
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if (ret && ret != -EOPNOTSUPP)
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return ret;
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if (dir->i_crypt_info) {
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ret = fscrypt_fname_alloc_buffer(dir, iname->len,
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&fname->crypto_buf);
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if (ret)
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return ret;
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ret = fname_encrypt(dir, iname, &fname->crypto_buf);
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if (ret)
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goto errout;
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fname->disk_name.name = fname->crypto_buf.name;
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fname->disk_name.len = fname->crypto_buf.len;
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return 0;
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}
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if (!lookup)
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return -EACCES;
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/*
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* We don't have the key and we are doing a lookup; decode the
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* user-supplied name
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*/
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if (iname->name[0] == '_')
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bigname = 1;
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if ((bigname && (iname->len != 33)) || (!bigname && (iname->len > 43)))
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return -ENOENT;
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fname->crypto_buf.name = kmalloc(32, GFP_KERNEL);
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if (fname->crypto_buf.name == NULL)
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return -ENOMEM;
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ret = digest_decode(iname->name + bigname, iname->len - bigname,
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fname->crypto_buf.name);
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if (ret < 0) {
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ret = -ENOENT;
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goto errout;
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}
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fname->crypto_buf.len = ret;
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if (bigname) {
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memcpy(&fname->hash, fname->crypto_buf.name, 4);
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memcpy(&fname->minor_hash, fname->crypto_buf.name + 4, 4);
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} else {
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fname->disk_name.name = fname->crypto_buf.name;
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fname->disk_name.len = fname->crypto_buf.len;
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}
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return 0;
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errout:
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fscrypt_fname_free_buffer(&fname->crypto_buf);
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return ret;
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}
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EXPORT_SYMBOL(fscrypt_setup_filename);
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void fscrypt_free_filename(struct fscrypt_name *fname)
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{
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kfree(fname->crypto_buf.name);
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fname->crypto_buf.name = NULL;
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fname->usr_fname = NULL;
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fname->disk_name.name = NULL;
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}
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EXPORT_SYMBOL(fscrypt_free_filename);
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