Re: [PATCH] KEYS: trusted: Reject short TPM2 public areas

[Jarkko Sakkinen <jarkko@kernel.org>]

On Fri, Sep 25, 2026 at 06:53:08PM +0900, Daehyeon Ko wrote:
> tpm2_load_cmd() reads TPMA_OBJECT with get_unaligned_be32(pub + 4), but
> does not require public_len to cover that field.
> 
> A new-format blob with public_len zero makes the read begin at the end of
> the B + 4-byte decoded allocation, causing a four-byte heap out-of-bounds
> read before the TPM command is transmitted. This is reachable from an
> unprivileged add_key() call when TPM trusted keys and a TPM2 device are
> available.
> 
> This affects v5.13-rc1 and later kernels built with CONFIG_TRUSTED_KEYS=y
> and CONFIG_TRUSTED_KEYS_TPM=y when a TPM2 device is present. A KASAN run
> as UID 1000 with no effective capabilities reported:
> 
> BUG: KASAN: slab-out-of-bounds in tpm2_unseal_trusted
> Read of size 4 at addr ffff888106273b48 by task exploit/160
> CPU: 1 UID: 1000 PID: 160 Comm: exploit
> The buggy address belongs to the object at ffff888106273b40
>  which belongs to the cache kmalloc-8 of size 8
> The buggy address is located 0 bytes to the right of
>  allocated 8-byte region [ffff888106273b40, ffff888106273b48)
> 
> TPMT_PUBLIC starts with the two-byte type, two-byte nameAlg and four-byte
> objectAttributes fields. Require public_len to cover all eight bytes before
> reading the attributes.
> 
> The exact input produced the KASAN read in 3/3 fresh boots. The fixed build
> rejected it with -E2BIG and no KASAN report in 3/3 boots; valid new- and
> old-format trusted-key loads continued to succeed.
> 
> Fixes: e5fb5d2c5a03 ("security: keys: trusted: Make sealed key properly interoperable")
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
> ---
> Tested with QEMU tpm-tis and swtpm: vulnerable 3/3 KASAN reports,
> fixed 3/3 clean -E2BIG rejections, with public_len 7/8 and new/old-format
> controls passing. Stable 5.15+ requires 114f00d738f1 first; both patches
> apply cleanly in that order.
> 
> The source reproducer and full logs are available privately on request.
> 
>  security/keys/trusted-keys/trusted_tpm2.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
> index c2a69bcf381d7..b3109e0a924f5 100644
> --- a/security/keys/trusted-keys/trusted_tpm2.c
> +++ b/security/keys/trusted-keys/trusted_tpm2.c
> @@ -418,6 +418,8 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
>  	public_len = get_unaligned_be16(blob + 2 + private_len);
>  	if (private_len + 2 + public_len + 2 > blob_len)
>  		return -E2BIG;
> +	if (public_len < 8)
> +		return -E2BIG;
>  
>  	pub = blob + 2 + private_len + 2;
>  	/* key attributes are always at offset 4 */
> 
> base-commit: 27d14d3b15d5691bcbf0683883a2ea12469edbea

Yeah, makes sense as those eight bytes is what covers the data needed
to identify the key.


Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

Thanks.

Br, Jarkko