Re: [PATCH 2/2] crypto: rsassa-pkcs1: reject undersized keys when verifying

[Sudhakar Kuppusamy]

> On 26 Aug 2026, at 4:07 PM, Jérémy Jean <Jeremy.Jean@xxxxxxxxxxxxxxxxx> wrote:
> 
> rsassa_pkcs1_verify() accepts any nonzero key size.
> 
> With a one-byte key and a zero RSA result, the leading-zero handling
> decrements dst_len to zero and advances out_buf past the allocation.
> The next out_buf[0] access reads out of bounds.
> 
> KASAN reports:
> 
>    BUG: KASAN: slab-out-of-bounds in rsassa_pkcs1_verify+0x79d/0x900
>    Read of size 1 at addr ...
>    The buggy address is located 0 bytes to the right of
>     allocated 73-byte region [...]
> 
> Reject keys shorter than the minimum PKCS#1 v1.5 encoded message size.
> 
> Fixes: 3d5b1ecdea6f ("crypto: rsa - RSA padding algorithm")
> Assisted-by: Codex:gpt-5
> Signed-off-by: Jérémy Jean <Jeremy.Jean@xxxxxxxxxxxxxxxxx>


Reviewed-by: Sudhakar Kuppusamy <sudhakar@xxxxxxxxxxxxx>


Thanks,
Sudhakar

> ---
> crypto/rsassa-pkcs1.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/crypto/rsassa-pkcs1.c b/crypto/rsassa-pkcs1.c
> index d0e4a885397f..39137476ce81 100644
> --- a/crypto/rsassa-pkcs1.c
> +++ b/crypto/rsassa-pkcs1.c
> @@ -231,7 +231,7 @@ static int rsassa_pkcs1_verify(struct crypto_sig *tfm,
> int err;
> 
> /* RFC 8017 sec 8.2.2 step 1 - length checking */
> - if (!ctx->key_size ||
> + if (ctx->key_size < 11 ||
>    slen != ctx->key_size ||
>    rsassa_pkcs1_invalid_hash_len(dlen, hash_prefix))
> return -EINVAL;
> -- 
> 2.47.3
> 
>