[PATCH v4 2/2] fs/aio: Make io_cancel() generate completions again

[Bart Van Assche <bvanassche@acm.org>]

The following patch accidentally removed the code for delivering
completions for cancelled reads and writes to user space: "[PATCH 04/33]
aio: remove retry-based AIO"
(https://lore.kernel.org/all/1363883754-27966-5-git-send-email-koverstreet@google.com/)
From that patch:

-	if (kiocbIsCancelled(iocb)) {
-		ret = -EINTR;
-		aio_complete(iocb, ret, 0);
-		/* must not access the iocb after this */
-		goto out;
-	}

This leads to a leak in user space of a struct iocb. Hence this patch
that restores the code that reports to user space that a read or write
has been cancelled successfully.

Fixes: 41003a7bcfed ("aio: remove retry-based AIO")
Cc: Christoph Hellwig <hch@lst.de>
Cc: Avi Kivity <avi@scylladb.com>
Cc: Sandeep Dhavale <dhavale@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 fs/aio.c | 27 +++++++++++----------------
 1 file changed, 11 insertions(+), 16 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index da18dbcfcb22..28223f511931 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -2165,14 +2165,11 @@ COMPAT_SYSCALL_DEFINE3(io_submit, compat_aio_context_t, ctx_id,
 #endif
 
 /* sys_io_cancel:
- *	Attempts to cancel an iocb previously passed to io_submit.  If
- *	the operation is successfully cancelled, the resulting event is
- *	copied into the memory pointed to by result without being placed
- *	into the completion queue and 0 is returned.  May fail with
- *	-EFAULT if any of the data structures pointed to are invalid.
- *	May fail with -EINVAL if aio_context specified by ctx_id is
- *	invalid.  May fail with -EAGAIN if the iocb specified was not
- *	cancelled.  Will fail with -ENOSYS if not implemented.
+ *	Attempts to cancel an iocb previously passed to io_submit(). If the
+ *	operation is successfully cancelled 0 is returned. May fail with
+ *	-EFAULT if any of the data structures pointed to are invalid. May
+ *	fail with -EINVAL if aio_context specified by ctx_id is invalid. Will
+ *	fail with -ENOSYS if not implemented.
  */
 SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
 		struct io_event __user *, result)
@@ -2203,14 +2200,12 @@ SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
 	}
 	spin_unlock_irq(&ctx->ctx_lock);
 
-	if (!ret) {
-		/*
-		 * The result argument is no longer used - the io_event is
-		 * always delivered via the ring buffer. -EINPROGRESS indicates
-		 * cancellation is progress:
-		 */
-		ret = -EINPROGRESS;
-	}
+	/*
+	 * The result argument is no longer used - the io_event is always
+	 * delivered via the ring buffer.
+	 */
+	if (ret == 0 && kiocb->rw.ki_flags & IOCB_AIO_RW)
+		aio_complete_rw(&kiocb->rw, -EINTR);
 
 	percpu_ref_put(&ctx->users);