Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 3c7018eb authored by Eric Biggers's avatar Eric Biggers Committed by Theodore Ts'o
Browse files

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: default avatarEric Biggers <ebiggers@google.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent bc33b0ca

fs/crypto/fname.c

+21 −32
Original line number Diff line number Diff line
@@ -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;

}