The Linux kernel's AF_ALG cryptographic API is removing zero-copy support from SKCIPHER and AEAD code due to security risks. Zero-copy in AF_ALG allows userspace to request crypto operations directly on pagecache pages (e.g., the 'su' binary) and enables concurrent memory modification, creating TOCTOU vulnerabilities. Google's Eric Biggers argues the risks far outweigh the benefits since AF_ALG is a niche interface primarily kept for backwards compatibility with a small set of programs like 'iwd'. The change is a soft break — splice() and sendfile() still work, but the kernel now makes an internal copy of data before crypto operations, slightly reducing performance while significantly improving safety. The patch is in the cryptodev tree and expected to land in Linux 7.2.
