eventpoll: abstract out parameter sanity checking

Add a helper that checks the validity of the file descriptor and
other parameters passed in to epoll_wait().

Signed-off-by: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/r/20250219172552.1565603-2-axboe@kernel.dk
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 7c0980db77b3178ae23699f0907bcbdaee44c458..565bf451df8232cf4cebceeb7eb2cdd20024565e 100644 (file)
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -2445,6 +2445,27 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
        return do_epoll_ctl(epfd, op, fd, &epds, false);
 }
 
+static int ep_check_params(struct file *file, struct epoll_event __user *evs,
+                          int maxevents)
+{
+       /* The maximum number of event must be greater than zero */
+       if (maxevents <= 0 || maxevents > EP_MAX_EVENTS)
+               return -EINVAL;
+
+       /* Verify that the area passed by the user is writeable */
+       if (!access_ok(evs, maxevents * sizeof(struct epoll_event)))
+               return -EFAULT;
+
+       /*
+        * We have to check that the file structure underneath the fd
+        * the user passed to us _is_ an eventpoll file.
+        */
+       if (!is_file_epoll(file))
+               return -EINVAL;
+
+       return 0;
+}
+
 /*
  * Implement the event wait interface for the eventpoll file. It is the kernel
  * part of the user space epoll_wait(2).
@@ -2453,26 +2474,16 @@ static int do_epoll_wait(int epfd, struct epoll_event __user *events,
                         int maxevents, struct timespec64 *to)
 {
        struct eventpoll *ep;
-
-       /* The maximum number of event must be greater than zero */
-       if (maxevents <= 0 || maxevents > EP_MAX_EVENTS)
-               return -EINVAL;
-
-       /* Verify that the area passed by the user is writeable */
-       if (!access_ok(events, maxevents * sizeof(struct epoll_event)))
-               return -EFAULT;
+       int ret;
 
        /* Get the "struct file *" for the eventpoll file */
        CLASS(fd, f)(epfd);
        if (fd_empty(f))
                return -EBADF;
 
-       /*
-        * We have to check that the file structure underneath the fd
-        * the user passed to us _is_ an eventpoll file.
-        */
-       if (!is_file_epoll(fd_file(f)))
-               return -EINVAL;
+       ret = ep_check_params(fd_file(f), events, maxevents);
+       if (unlikely(ret))
+               return ret;
 
        /*
         * At this point it is safe to assume that the "private_data" contains