fscrypto: don't use on-stack buffer for key derivation (a6e08912) · Commits · 戴 / test

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:

Eric Biggers <ebiggers@google.com> Signed-off-by:

Theodore Ts'o <tytso@mit.edu>

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 @@ retry:
		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 @@ got_key:
		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 @@ out:
		if (res == -ENOKEY)
		res = 0;
		put_crypt_info(crypt_info);
		memzero_explicit(raw_key, sizeof(raw_key));
		kzfree(raw_key);
		return res;
		}

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