[PATCH 7.2 33/88] io_uring/cancel: recognize "no timeout" on 32-bit

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

7.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Josef Bacik <josef@toxicpanda.com>

Commit 3774e4d4c8533da2caae95556c4d635c7c4f45b8 upstream.

IORING_REGISTER_SYNC_CANCEL waits without a limit if both fields of
io_uring_sync_cancel_reg::timeout are -1. io_sync_cancel() compares them
with -1UL. They are of type long long. With a long of 32 bits -1UL is
4294967295, which is what it stays when it is converted for the
comparison, and the fields are never equal to it.

So { -1, -1 } is taken for a timeout. ktime_set() takes the nanoseconds as
an unsigned long, so what becomes of it is -1s + 4294967295ns = 3.29s.

If the request is being run by io-wq and can't be interrupted, the call
returns -ETIME after that time, rather than waiting for the request to be
gone. On i386, with a buffered read from a null_blk device that takes 4s
to complete a request, IOSQE_ASYNC, that is what each call does.

Fixes: 78a861b94959 ("io_uring: add sync cancelation API through io_uring_register()")
Assisted-by: LLM
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Link: https://patch.msgid.link/20261015-b4-io-uring-fixes-v1-17-c1556f5d7bf5@toxicpanda.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 io_uring/cancel.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/io_uring/cancel.c
+++ b/io_uring/cancel.c
@@ -319,7 +319,7 @@ int io_sync_cancel(struct io_ring_ctx *c
 	if (ret != -EALREADY)
 		goto out;
 
-	if (sc.timeout.tv_sec != -1UL || sc.timeout.tv_nsec != -1UL) {
+	if (sc.timeout.tv_sec != -1 || sc.timeout.tv_nsec != -1) {
 		struct timespec64 ts = {
 			.tv_sec		= sc.timeout.tv_sec,
 			.tv_nsec	= sc.timeout.tv_nsec