iov_iter: fix copy_page_from_iter_atomic() if KMAP_LOCAL_FORCE_MAP

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: iov_iter: fix copy_page_from_iter_atomic() if KMAP_LOCAL_FORCE_MAP generic/077 on x86_32 CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP=y with highmem, on huge=always tmpfs, issues a warning and then hangs (interruptibly): WARNING: CPU: 5 PID: 3517 at mm/highmem.c:622 kunmap_local_indexed+0x62/0xc9 CPU: 5 UID: 0 PID: 3517 Comm: cp Not tainted 6.12.0-rc4 #2 ... copy_page_from_iter_atomic+0xa6/0x5ec generic_perform_write+0xf6/0x1b4 shmem_file_write_iter+0x54/0x67 Fix copy_page_from_iter_atomic() by limiting it in that case (include/linux/skbuff.h skb_frag_must_loop() does similar). But going forward, perhaps CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP is too surprising, has outlived its usefulness, and should just be removed?

References

• https://git.kernel.org/stable/c/4f7ffa83fa79dd52efbaef366c850aaaae06a469
• https://git.kernel.org/stable/c/3a303409f271dfe0987b8f79595138340497a32d
• https://git.kernel.org/stable/c/c749d9b7ebbc5716af7a95f7768634b30d9446ec