select: store end_time as timespec64 in restart block

Storing the end time seconds as 'unsigned long' can lead to truncation
on 32-bit architectures if assigned from the 64-bit timespec64::tv_sec.
As the select() core uses timespec64 consistently, also use that in the
restart block.

This also allows the simplification of the accessors.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Link: https://patch.msgid.link/20251223-restart-block-expiration-v2-1-8e33e5df7359@linutronix.de
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: t-8ch

fs/select.c

@@ -1038,14 +1038,11 @@ static long do_restart_poll(struct restart_block *restart_block)
 {
 	struct pollfd __user *ufds = restart_block->poll.ufds;
 	int nfds = restart_block->poll.nfds;
-	struct timespec64 *to = NULL, end_time;
+	struct timespec64 *to = NULL;
 	int ret;
 
-	if (restart_block->poll.has_timeout) {
-		end_time.tv_sec = restart_block->poll.tv_sec;
-		end_time.tv_nsec = restart_block->poll.tv_nsec;
-		to = &end_time;
-	}
+	if (restart_block->poll.has_timeout)
+		to = &restart_block->poll.end_time;
 
 	ret = do_sys_poll(ufds, nfds, to);
 
@@ -1077,8 +1074,7 @@ SYSCALL_DEFINE3(poll, struct pollfd __user *, ufds, unsigned int, nfds,
 		restart_block->poll.nfds = nfds;
 
 		if (timeout_msecs >= 0) {
-			restart_block->poll.tv_sec = end_time.tv_sec;
-			restart_block->poll.tv_nsec = end_time.tv_nsec;
+			restart_block->poll.end_time = end_time;
 			restart_block->poll.has_timeout = 1;
 		} else
 			restart_block->poll.has_timeout = 0;

include/linux/restart_block.h

@@ -6,6 +6,7 @@
 #define __LINUX_RESTART_BLOCK_H
 
 #include <linux/compiler.h>
+#include <linux/time64.h>
 #include <linux/types.h>
 
 struct __kernel_timespec;
@@ -50,8 +51,7 @@ struct restart_block {
 			struct pollfd __user *ufds;
 			int nfds;
 			int has_timeout;
-			unsigned long tv_sec;
-			unsigned long tv_nsec;
+			struct timespec64 end_time;
 		} poll;
 	};
 };