On 1/18/22 15:03, Ilias Apalodimas wrote:
Hi Heinrich,
- info.checksum = image_get_checksum_algo("sha256,rsa2048");
[...]
- info.name = "sha256,rsa2048";
- } else {
- pr_warn("unknown msg digest algo: %s\n", sig->hash_algo);
+ if (strcmp(sig->pkey_algo, "rsa")) {
+ pr_err("Encryption is not RSA: %s\n", sig->pkey_algo);
return -ENOPKG;
}
+ ret = snprintf(algo, sizeof(algo), "%s,%s%d", sig->hash_algo,
+ sig->pkey_algo, sig->s_size * 8);
How do we ensure that the unsafe SHA1 algorithm is not used?
We don't, but the current code allows it as well. Should we enforce this
from U-Boot though? The spec doesn't forbid it as far as I remember
Collisions for SHA1 have been first created successfully in 2017.
It is feasible to create two different EFI binaries with the same SHA1.
One will be reviewed and signed. After copying the signature to the
other one it will happily boot on U-Boot. Ouch. This is exactly what
signatures are meant to avoid.
We must not accept SHA1 for signatures.
Best regards
Heinrich
Regards
/Ilias
Best regards
Heinrich
I'm not sure that this naming rule, in particular the latter part, will
always hold in the future while all the existing algo's observe it.
(Maybe we need some note somewhere?)
The if a few lines below will shield us and return -EINVAL. How about
adding an error message there?
Cheers
/Ilias
-Takahiro Akashi
+
+ if (ret >= sizeof(algo))
+ return -EINVAL;
+
+ info.checksum = image_get_checksum_algo((const char *)algo);
+ info.name = (const char *)algo;
info.crypto = image_get_crypto_algo(info.name);
- if (IS_ERR(info.checksum) || IS_ERR(info.crypto))
+ if (!info.checksum || !info.crypto)
return -ENOPKG;
info.key = pkey->key;
--
2.30.2
