[PATCH 2/2] io_uring/wait: honour caller's time namespace for IORING_ENTER_ABS_TIMER

[Maoyi Xie]

io_uring_enter() with IORING_ENTER_ABS_TIMER takes an absolute
timespec from the caller via ext_arg->ts. It arms an ABS mode
hrtimer in __io_cqring_wait_schedule(). The conversion path in
io_uring/wait.c parses ext_arg->ts inline rather than going
through io_parse_user_time(). It therefore does not pick up the
time namespace conversion added by the previous patch.

Apply timens_ktime_to_host() to the parsed time on the
IORING_ENTER_ABS_TIMER branch. This mirrors the IORING_TIMEOUT_ABS
fix in io_parse_user_time(). Use ctx->clockid as the clock id.
ctx->clockid is set either at ring creation or via
IORING_REGISTER_CLOCK.

timens_ktime_to_host() is a no-op for clocks not affected by time
namespaces. It is also a no-op for callers in the initial time
namespace. The fast path is unchanged.

Reproducer: in unshare --user --time, with a -10s monotonic
offset, call io_uring_enter with min_complete=1,
IORING_ENTER_ABS_TIMER, and ts = now + 1s. The call returns
-ETIME after <1ms instead of after the expected ~1s.

Suggested-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
Suggested-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Maoyi Xie <maoyi.xie@xxxxxxxxxx>
---
 io_uring/wait.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/io_uring/wait.c b/io_uring/wait.c
index 91df86ce0..ec01e78a2 100644
--- a/io_uring/wait.c
+++ b/io_uring/wait.c
@@ -5,6 +5,7 @@
 #include <linux/kernel.h>
 #include <linux/sched/signal.h>
 #include <linux/io_uring.h>
+#include <linux/time_namespace.h>
 
 #include <trace/events/io_uring.h>
 
@@ -229,7 +230,10 @@ int io_cqring_wait(struct io_ring_ctx *ctx, int min_events, u32 flags,
 
 	if (ext_arg->ts_set) {
 		iowq.timeout = timespec64_to_ktime(ext_arg->ts);
-		if (!(flags & IORING_ENTER_ABS_TIMER))
+		if (flags & IORING_ENTER_ABS_TIMER)
+			iowq.timeout = timens_ktime_to_host(ctx->clockid,
+							    iowq.timeout);
+		else
 			iowq.timeout = ktime_add(iowq.timeout, start_time);
 	}
 
-- 
2.34.1