serialize: Change GetSerializeSize return type to uint64_t #33712

1. 
   sshivanshg commented at 10:22 am on October 27, 2025: none

   GetSerializeSize currently returns size_t, which is platform-dependent. On 32-bit systems, size_t is 32-bit, limiting the maximum serialized size to ~4GB. This can cause integer overflow when multiplying by WITNESS_SCALE_FACTOR during block size validation. Change GetSerializeSize to return uint64_t to ensure it can handle large sizes without overflow on all platforms. This fixes CVE-2025-46597. Resolves: #33709
2. serialize: Change GetSerializeSize return type to uint64_t

   GetSerializeSize currently returns size_t, which is platform-dependent.
   On 32-bit systems, size_t is 32-bit, limiting the maximum serialized
   size to ~4GB. This can cause integer overflow when multiplying by
   WITNESS_SCALE_FACTOR during block size validation.
   
   Change GetSerializeSize to return uint64_t to ensure it can handle
   large sizes without overflow on all platforms.
   
   This fixes CVE-2025-46597.

   3f2ec023d3
3. 
   DrahtBot commented at 10:22 am on October 27, 2025: contributor

   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/33712.

   Reviews

   See the guideline for information on the review process. A summary of reviews will appear here.

4. 
   pinheadmz commented at 11:23 am on October 27, 2025: member

   @sshivanshg because this code is so critical, your PR description should be more detailed. Especially since you are a first-time contributor with no merit. Please respond with a detailed explanation of your understanding of the issue, steps you took to solve the issue, how you tested your code, and how reviewers should test your code.

   This likely needs to be done before anyone seriously reviews your pull request. Otherwise it will be closed due to inactivity, and a more responsible human author will take it over.

   See https://github.com/bitcoin/bitcoin/blob/master/CONTRIBUTING.md

5. sshivanshg closed this on Oct 27, 2025

   ---

6. sshivanshg deleted the branch on Oct 27, 2025
7. bitcoin locked this on Oct 28, 2025

Contributors
sshivanshg DrahtBot pinheadmz