GCC 12's -Wstringop-overflow flags issues in SHA224_Final, etc., because
it calls into generic code that might output a SHA-224 length or a
SHA-256 length, and the function prototype declares the array is only
sized for SHA-224.
This is a bit messy because OpenSSL's API for the truncated SHA-2 hashes
allows you to mix and match them. The output size is set by SHA224_Init
and then, originally, SHA256_Final and SHA224_Final were the same thing.
See how OpenSSL's own SHA224 function calls SHA224_Init + SHA256_Final:
https://github.com/openssl/openssl/blob/OpenSSL_1_1_1q/crypto/sha/sha256.c#L49-L61
To get the function prototype bounds to work out, we tightened this
slightly in
https://boringssl-review.googlesource.com/c/boringssl/+/47807 and added
an assert to SHA224_Final that ctx->md_len was the right size.
SHA256_Final does not have that assert yet. The assert says that mixing
SHA256_Init and SHA224_Final is a caller error.
This isn't good enough for GCC 12, which checks bounds assuming there is
no external invariant on ctx->md_len. This CL changes the behavior of
the shorter Final functions: they will now always output the length
implied by the function name. ctx->md_len only figures into an assert()
call. As we don't have the assert in the untruncated functions yet, I've
preserved their behavior, but the test run with cl/471617180 should tell
us whether apply this to all functions is feasible.
Update-Note: Truncated SHA-2 Final functions change behavior slightly,
but anyone affected by this behavior change would already have tripped
an assert() in debug builds.
Change-Id: I80fdcbe6ad76bc8713c0f2de329b958a2b35e8ae
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/54246
Auto-Submit: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>
David Benjamin
2749466282