All PKEY methods implementing signing or secure hashing should fail if the value for siglen is too small

[reiniert]

The documentation for EVP_DigestSignFinal() mentions the following precondition:

If sig is not NULL then before the call the siglen parameter should contain the length of the sig buffer.

This implies that the siglen parameter actually has some significance and is being checked to be sufficiently large by the function(s) that fill(s) the sig buffer. The expectation is that the function fails if that check fails. Indeed, this mechanism can be observed here:

openssl/crypto/ec/ec_pmeth.c

Line 118 in e2e09d9

if (*siglen < (size_t)sig_sz) {

However, most PKEY sign(-like) methods do not seem to include such a check. For example see

openssl/crypto/hmac/hm_pmeth.c

Line 127 in 894da2f

*siglen = l;

[nhorman]

the hmac code is significantly altered in openssl-3.x, is this still an issue?