Messages in this thread Patch in this message | | | Date | Fri, 16 Mar 2018 08:21:08 -0500 | From | "Gustavo A. R. Silva" <> | Subject | [PATCH v2] USB: wusbcore: crypto: Remove VLA usage |
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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> --- Changes in v2: - Fix a memory leak in previous patch.
drivers/usb/wusbcore/crypto.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/drivers/usb/wusbcore/crypto.c b/drivers/usb/wusbcore/crypto.c index 4c00be2d..aff50eb 100644 --- a/drivers/usb/wusbcore/crypto.c +++ b/drivers/usb/wusbcore/crypto.c @@ -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; -- 2.7.4
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