Fixed crash when loading a PKCS#7 bundle with no certificates #9926
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| @@ -1111,9 +1111,12 @@ def _load_pkcs7_certificates(self, p7) -> list[x509.Certificate]: | |||
| _Reasons.UNSUPPORTED_SERIALIZATION, | |||
| ) | |||
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| certs: list[x509.Certificate] = [] | |||
| if p7.d.sign == self._ffi.NULL: | |||
| return certs | |||
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I don't think this fix is quite right. I believe this should actually raise an exception here, not return the empty list, because it's analogous to the block above, where you reject content types other than signed data.
Specifically, this is NULL if you've got a content-less ContentInfo:
https://datatracker.ietf.org/doc/html/rfc2315#section-7
The spec says:
o content is the content. The field is optional, and
if the field is not present, its intended value must be
supplied by other means. Its type is defined along with the
object identifier for contentType.
It honestly doesn't make any sense for the signed-data ContentInfos that you're parsing here. It's more for the data ContentInfo inside the signed-data ContentInfo. As the spec says later on here:
3. The optional omission of the content field makes
it possible to construct "external signatures," for
example, without modification to or replication of the
content to which the signatures apply. In the case of
external signatures, the content being signed would be
omitted from the "inner" encapsulated ContentInfo value
included in the signed-data content type.
That is, an omitted one means "this is a signed data, but I am omitting the signature, certificates, etc., with the expectation that you have it out of band somewhere".
Setting aside whether there are any use cases for that, it certainly doesn't make sense in the context of your function. By returning the empty list, you are telling the caller "yup, this contained zero certificates!". But this actually may have contained a ton of certificates, you just didn't have them available. So this is actually a PKCS#7 blob that isn't of the type you expect.
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I should add that, as far as compatibility goes, nothing can possibly be relying on you returning the empty list here because it used to crash. :-)
as davidben points out in pyca#9926 we are calling a specific load certificates function and an empty value doesn't necessarily mean empty because PKCS7 contains multitudes. erroring is more correct.
…loading (#9947) * raise an exception instead of returning an empty list as davidben points out in #9926 we are calling a specific load certificates function and an empty value doesn't necessarily mean empty because PKCS7 contains multitudes. erroring is more correct. * changelog * Update CHANGELOG.rst Co-authored-by: Alex Gaynor <[email protected]> --------- Co-authored-by: Alex Gaynor <[email protected]>
…loading (pyca#9947) * raise an exception instead of returning an empty list as davidben points out in pyca#9926 we are calling a specific load certificates function and an empty value doesn't necessarily mean empty because PKCS7 contains multitudes. erroring is more correct. * changelog * Update CHANGELOG.rst Co-authored-by: Alex Gaynor <[email protected]> --------- Co-authored-by: Alex Gaynor <[email protected]>
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