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
Signed-off-by: Gustavo A. R. Silva <[email protected]>
---
net/bluetooth/smp.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index a2ddae2..23c694d 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -173,7 +173,7 @@ static int aes_cmac(struct crypto_shash *tfm, const u8 k[16], const u8 *m,
size_t len, u8 mac[16])
{
uint8_t tmp[16], mac_msb[16], msg_msb[CMAC_MSG_MAX];
- SHASH_DESC_ON_STACK(desc, tfm);
+ struct shash_desc *shash;
int err;
if (len > CMAC_MSG_MAX)
@@ -184,8 +184,13 @@ static int aes_cmac(struct crypto_shash *tfm, const u8 k[16], const u8 *m,
return -EINVAL;
}
- desc->tfm = tfm;
- desc->flags = 0;
+ shash = kzalloc(sizeof(*shash) + crypto_shash_descsize(tfm),
+ GFP_KERNEL);
+ if (!shash)
+ return -ENOMEM;
+
+ shash->tfm = tfm;
+ shash->flags = 0;
/* Swap key and message from LSB to MSB */
swap_buf(k, tmp, 16);
@@ -200,8 +205,9 @@ static int aes_cmac(struct crypto_shash *tfm, const u8 k[16], const u8 *m,
return err;
}
- err = crypto_shash_digest(desc, msg_msb, len, mac_msb);
- shash_desc_zero(desc);
+ err = crypto_shash_digest(shash, msg_msb, len, mac_msb);
+ shash_desc_zero(shash);
+ kfree(shash);
if (err) {
BT_ERR("Hash computation error %d", err);
return err;
--
2.7.4
Hi,
I've just discovered an issue in this patch. Please, drop it. I'll send
v2 shortly.
Thanks
--
Gustavo
On 03/20/2018 06:34 PM, Gustavo A. R. Silva wrote:
> 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
>
> Signed-off-by: Gustavo A. R. Silva <[email protected]>
> ---
> net/bluetooth/smp.c | 16 +++++++++++-----
> 1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
> index a2ddae2..23c694d 100644
> --- a/net/bluetooth/smp.c
> +++ b/net/bluetooth/smp.c
> @@ -173,7 +173,7 @@ static int aes_cmac(struct crypto_shash *tfm, const u8 k[16], const u8 *m,
> size_t len, u8 mac[16])
> {
> uint8_t tmp[16], mac_msb[16], msg_msb[CMAC_MSG_MAX];
> - SHASH_DESC_ON_STACK(desc, tfm);
> + struct shash_desc *shash;
> int err;
>
> if (len > CMAC_MSG_MAX)
> @@ -184,8 +184,13 @@ static int aes_cmac(struct crypto_shash *tfm, const u8 k[16], const u8 *m,
> return -EINVAL;
> }
>
> - desc->tfm = tfm;
> - desc->flags = 0;
> + shash = kzalloc(sizeof(*shash) + crypto_shash_descsize(tfm),
> + GFP_KERNEL);
> + if (!shash)
> + return -ENOMEM;
> +
> + shash->tfm = tfm;
> + shash->flags = 0;
>
> /* Swap key and message from LSB to MSB */
> swap_buf(k, tmp, 16);
> @@ -200,8 +205,9 @@ static int aes_cmac(struct crypto_shash *tfm, const u8 k[16], const u8 *m,
> return err;
> }
>
> - err = crypto_shash_digest(desc, msg_msb, len, mac_msb);
> - shash_desc_zero(desc);
> + err = crypto_shash_digest(shash, msg_msb, len, mac_msb);
> + shash_desc_zero(shash);
> + kfree(shash);
> if (err) {
> BT_ERR("Hash computation error %d", err);
> return err;
>