Re: [PATCH v1 2/2] epoll: Use __user_write_access_begin() and unsafe_put_user() in epoll_put_uevent().
From: Dave Hansen <hidden>
Date: 2025-10-23 19:41:01
Also in:
linux-arm-kernel, linux-riscv, lkml
On 10/22/25 17:04, Kuniyuki Iwashima wrote:
quoted hunk ↗ jump to hunk
--- a/include/linux/eventpoll.h +++ b/include/linux/eventpoll.h@@ -82,11 +82,14 @@ static inline struct epoll_event __user * epoll_put_uevent(__poll_t revents, __u64 data, struct epoll_event __user *uevent) { - if (__put_user(revents, &uevent->events) || - __put_user(data, &uevent->data)) - return NULL; - - return uevent+1; + __user_write_access_begin(uevent, sizeof(*uevent)); + unsafe_put_user(revents, &uevent->events, efault); + unsafe_put_user(data, &uevent->data, efault); + user_access_end(); + return uevent + 1; +efault: + user_access_end(); + return NULL; } #endif
This makes me nervous. The access_ok() check is quite a distance away. I'd kinda want to see some performance numbers before doing this. Is removing a single access_ok() even measurable? Also, even if we go do this, shouldn't __user_write_access_begin() be called something more like unsafe_user_write_access_begin()?