Commit 225b3dc9 authored Mar 16, 2018 by Gustavo A. R. Silva Committed by Greg Kroah-Hartman Mar 16, 2018

USB: wusbcore: crypto: Remove VLA usage

In preparation to enabling -Wvla, remove VLA and replace it
with dynamic memory allocation instead.

The use of stack Variable Length Arrays needs to be avoided, as they
can be a vector for stack exhaustion, which can be both a runtime bug
or a security flaw. Also, in general, as code evolves it is easy to
lose track of how big a VLA can get. Thus, we can end up having runtime
failures that are hard to debug.

Also, fixed as part of the directive to remove all VLAs from
the kernel: https://lkml.org/lkml/2018/3/7/621



Notice that in this particular case, an alternative to kzalloc is kcalloc,
in which case the code would look as follows instead:

iv = kcalloc(crypto_skcipher_ivsize(tfm_cbc), sizeof(*iv), GFP_KERNEL);

but if the data type of _iv_ never changes, or the type size is always one
byte, kzalloc is good enough.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 7bb9aeda

drivers/usb/wusbcore/crypto.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -202,7 +202,7 @@ static int wusb_ccm_mac(struct crypto_skcipher *tfm_cbc,
		struct scatterlist sg[4], sg_dst;
		void *dst_buf;
		size_t dst_size;
		u8 iv[crypto_skcipher_ivsize(tfm_cbc)];
		u8 *iv;
		size_t zero_padding;

		/*
		@@ -224,7 +224,9 @@ static int wusb_ccm_mac(struct crypto_skcipher *tfm_cbc,
		if (!dst_buf)
		goto error_dst_buf;

		memset(iv, 0, sizeof(iv));
		iv = kzalloc(crypto_skcipher_ivsize(tfm_cbc), GFP_KERNEL);
		if (!iv)
		goto error_iv;

		/* Setup B0 */
		scratch->b0.flags = 0x59; /* Format B0 */
		@@ -276,6 +278,8 @@ static int wusb_ccm_mac(struct crypto_skcipher *tfm_cbc,
		bytewise_xor(mic, &scratch->ax, iv, 8);
		result = 8;
		error_cbc_crypt:
		kfree(iv);
		error_iv:
		kfree(dst_buf);
		error_dst_buf:
		return result;