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Commit 0f0909e2 authored by Eric Biggers's avatar Eric Biggers Committed by Theodore Ts'o
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fscrypto: don't use on-stack buffer for key derivation 



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.  get_crypt_info() was using a stack buffer to hold the
output from the encryption operation used to derive the per-file key.
Fix it by using a heap buffer.

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 3c7018eb

fs/crypto/keyinfo.c

+13 −3
Original line number Diff line number Diff line
@@ -185,7 +185,7 @@ int get_crypt_info(struct inode *inode) 
	struct crypto_skcipher *ctfm;

	const char *cipher_str;

	int keysize;

	u8 raw_key[FS_MAX_KEY_SIZE];

	u8 *raw_key = NULL;

	int res;



	res = fscrypt_initialize();
@@ -238,6 +238,15 @@ int get_crypt_info(struct inode *inode) 
	if (res)

		goto out;



	/*

	 * This cannot be a stack buffer because it is passed to the scatterlist

	 * crypto API as part of key derivation.

	 */

	res = -ENOMEM;

	raw_key = kmalloc(FS_MAX_KEY_SIZE, GFP_NOFS);

	if (!raw_key)

		goto out;



	if (fscrypt_dummy_context_enabled(inode)) {

		memset(raw_key, 0x42, FS_AES_256_XTS_KEY_SIZE);

		goto got_key;
@@ -276,7 +285,8 @@ int get_crypt_info(struct inode *inode) 
	if (res)

		goto out;



	memzero_explicit(raw_key, sizeof(raw_key));

	kzfree(raw_key);

	raw_key = NULL;

	if (cmpxchg(&inode->i_crypt_info, NULL, crypt_info) != NULL) {

		put_crypt_info(crypt_info);

		goto retry;
@@ -287,7 +297,7 @@ int get_crypt_info(struct inode *inode) 
	if (res == -ENOKEY)

		res = 0;

	put_crypt_info(crypt_info);

	memzero_explicit(raw_key, sizeof(raw_key));

	kzfree(raw_key);

	return res;

}