Re: [PATCH] crypto: Prevent kernel-infoleak in rng_recvmsg

[Herbert Xu]

On Sat, Aug 09, 2025 at 05:59:43PM +0800, Edward Adam Davis wrote:
> Initialize the intermediary array member to 0 to prevent the kernel from
> leaking uninitialized data to user space.
> 
> Reported-by: syzbot+e8bcd7ee3db6cb5cb875@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=e8bcd7ee3db6cb5cb875
> Tested-by: syzbot+e8bcd7ee3db6cb5cb875@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
> ---
>  crypto/jitterentropy-kcapi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/crypto/jitterentropy-kcapi.c b/crypto/jitterentropy-kcapi.c
> index c24d4ff2b4a8..9e9e069f55af 100644
> --- a/crypto/jitterentropy-kcapi.c
> +++ b/crypto/jitterentropy-kcapi.c
> @@ -107,7 +107,7 @@ int jent_hash_time(void *hash_state, __u64 time, u8 *addtl,
>  {
>  	struct shash_desc *hash_state_desc = (struct shash_desc *)hash_state;
>  	SHASH_DESC_ON_STACK(desc, hash_state_desc->tfm);
> -	u8 intermediary[SHA3_256_DIGEST_SIZE];
> +	u8 intermediary[SHA3_256_DIGEST_SIZE] = { 0 };

This is not a leak! The stack memroy is hashed and fed into the
entropy pool.  If you can recover the original kernel memory from
the result, then we have much bigger problems :)

Please find a way to mark this as a false positive.

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