Re: [PATCH 1/3] KEYS: asym_tpm: fix buffer overreads in extract_key_parameters()

[Jarkko Sakkinen <jarkko@kernel.org>]

On Thu, Jan 13, 2022 at 03:54:38PM -0800, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> extract_key_parameters() can read past the end of the input buffer due
> to buggy and missing bounds checks.  Fix it as follows:
> 
> - Before reading each key length field, verify that there are at least 4
>   bytes remaining.

Maybe start with a "Key length is described as an unsigned 32-bit integer
in the TPM header". Just for clarity.

> 
> - Avoid integer overflows when validating size fields; 'sz + 12' and
>   '4 + sz' overflowed if 'sz' is near U32_MAX.

So we have a struct tpm_header in include/linux/tpm.h. It would be way
more informative to use sizeof(struct tpm_header) than number 12, even
if the patch does not otherwise use the struct. It tells what it is, 12
does not.

> - Before saving the pointer to the public key, check that it doesn't run
>   past the end of the buffer.
> 
> Fixes: f8c54e1ac4b8 ("KEYS: asym_tpm: extract key size & public key [ver #2]")
> Cc: <stable@vger.kernel.org> # v4.20+
> Signed-off-by: Eric Biggers <ebiggers@google.com>

BR, Jarkko