Medium [CVE-2026-74689] fix slab-out-of-bounds read in vcc_setsockopt

In the Linux kernel, the following vulnerability has been resolved: net/atm: fix slab-out-of-bounds read in vcc_setsockopt() vcc_setsockopt() contained an ineffective optlen check: if (__SO_LEVEL_MATCH(optname, level) && optlen!= __SO_SIZE(optname)) return -EINVAL; If __SO_LEVEL_MATCH(optname, level) evaluated to false (e.g. if the caller passed a mismatched level), the length check optlen!= __SO_SIZE(optname) was short-circuited and bypassed.

Execution then fell through to switch(optname), calling copy_from_sockptr() assuming optval contained sufficient space. Furthermore, even if level matched, a cgroup BPF setsockopt filter could shrink optlen after entry.

Because copy_from_sockptr() on kernel pointers uses memcpy(), this leads to a KASAN slab-out-of-bounds read when optlen is smaller than the expected structure size. Fix this by using copy_safe_from_sockptr(), which unconditionally validates that optlen is at least the expected size before copying.

Also change the local 'value' variable type from 'unsigned long' to 'int' so that SO_SETCLP matches its sizeof(int) ABI encoding on 64-bit systems. An ineffective length check in the `vcc_setsockopt()` function within the Asynchronous Transfer Mode (ATM) network protocol implementation can lead to a slab-out-of-bounds read.