[SRU][F][PATCH 1/1] io_uring: ensure IOPOLL locks around deferred work

[Chengen Du]

From: Jens Axboe <axboe at kernel.dk>

CVE-2023-21400

BugLink: https://bugs.launchpad.net/bugs/2078659

No direct upstream commit exists for this issue. It was fixed in
5.18 as part of a larger rework of the completion side.

io_commit_cqring() writes the CQ ring tail to make it visible, but it
also kicks off any deferred work we have. A ring setup with IOPOLL
does not need any locking around the CQ ring updates, as we're always
under the ctx uring_lock. But if we have deferred work that needs
processing, then io_queue_deferred() assumes that the completion_lock
is held, as it is for !IOPOLL.

Add a lockdep assertion to check and document this fact, and have
io_iopoll_complete() check if we have deferred work and run that
separately with the appropriate lock grabbed.

Cc: stable at vger.kernel.org # 5.10, 5.15
Reported-by: dghost david <daviduniverse18 at gmail.com>
Signed-off-by: Jens Axboe <axboe at kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(backported from commit fb348857e7b67eefe365052f1423427b66dedbf3)
[chengen - apply the locking logic to the corresponding functions /
use spin_lock_irq because the same lock is used in the timer callback
function.]
Signed-off-by: Chengen Du <chengen.du at canonical.com>
---
 fs/io_uring.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 875dd8e0f766..aa75c32f2d16 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -512,6 +512,8 @@ static void __io_commit_cqring(struct io_ring_ctx *ctx)
 {
 	struct io_rings *rings = ctx->rings;
 
+	lockdep_assert_held(&ctx->completion_lock);
+
 	if (ctx->cached_cq_tail != READ_ONCE(rings->cq.tail)) {
 		/* order cqe stores with ring update */
 		smp_store_release(&rings->cq.tail, ctx->cached_cq_tail);
@@ -841,7 +843,9 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
 		}
 	}
 
+	spin_lock_irq(&ctx->completion_lock);
 	io_commit_cqring(ctx);
+	spin_unlock_irq(&ctx->completion_lock);
 	io_free_req_many(ctx, reqs, &to_free);
 }
 
-- 
2.43.0