linux-kernel - Re: [PATCH] crypto: vmac - Handle unaligned input in vmac

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Message-ID: <Z24D7cvRovlFKISX@gondor.apana.org.au>
Date: Fri, 27 Dec 2024 09:33:33 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Atharva Tiwari <evepolonium@...il.com>
Cc: "David S. Miller" <davem@...emloft.net>, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] crypto: vmac - Handle unaligned input in vmac_update

On Thu, Dec 26, 2024 at 10:30:49PM +0530, Atharva Tiwari wrote:
> The `vmac_update` function previously assumed that `p` was aligned,
> which could lead to misaligned memory accesses when processing blocks.
> This patch resolves the issue by, 
> introducing a temporary buffer to ensure alignment.
> 
> Changes include:
> - Allocating a temporary buffer (`__le64 *data`) to store aligned blocks.
> - Using `get_unaligned_le64` to safely read data into the temporary buffer.
> - Iteratively processing blocks with the `vhash_blocks` function.
> - Properly freeing the allocated temporary buffer after processing.
> 
> Signed-off-by: Atharva Tiwari <evepolonium@...il.com>
> ---
>  crypto/vmac.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/crypto/vmac.c b/crypto/vmac.c
> index 2ea384645ecf..513fbd5bc581 100644
> --- a/crypto/vmac.c
> +++ b/crypto/vmac.c
> @@ -518,9 +518,19 @@ static int vmac_update(struct shash_desc *desc, const u8 *p, unsigned int len)
>  
>  	if (len >= VMAC_NHBYTES) {
>  		n = round_down(len, VMAC_NHBYTES);
> -		/* TODO: 'p' may be misaligned here */
> -		vhash_blocks(tctx, dctx, (const __le64 *)p, n / VMAC_NHBYTES);
> -		p += n;
> +		const u8 *end = p + n;
> +		const uint16_t num_blocks = VMAC_NHBYTES/sizeof(__le64);
> +		__le64 *data = kmalloc(num_blocks * sizeof(__le64), GFP_KERNEL);
> +
> +		while (p < end) {
> +			for (unsigned short i = 0; i < num_blocks; i++) {
> +				data[i] = get_unaligned_le64(p + i * sizeof(__le64));
> +			}

This is not what I meant by using get_unaligned_le64.  I meant
replacing the actual 64-bit accesses within vhash_blocks with
get_unaligned_le64.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt