FAILED: patch "[PATCH] iommufd: Fix event queue release use-after-free" failed to apply to 6.12-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x 440ca8a4b69f40088065b9e05ef11373292a254e
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026110435-fastball-maroon-2fc3@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 440ca8a4b69f40088065b9e05ef11373292a254e Mon Sep 17 00:00:00 2001
From: Nirmoy Das <nirmoyd@nvidia.com>
Date: Wed, 14 Oct 2026 06:36:32 -0700
Subject: [PATCH] iommufd: Fix event queue release use-after-free

iommufd_eventq_fops_release() drops the file's users reference before
reading eventq->ictx. Once that reference is dropped, IOMMU_DESTROY in
another thread can remove and free the event queue, so the later load
accesses freed memory.

Read ictx while the users reference still pins the event queue, then
drop the reference and put the saved context. The context reference
taken by iommufd_eventq_init() keeps ictx valid until the put. Fault and
vEVENTQ file descriptors share this release path.

Fixes: 07838f7fd529 ("iommufd: Add iommufd fault object")
Cc: stable@vger.kernel.org
Assisted-by: LLM, Specula
Signed-off-by: Nirmoy Das <nirmoyd@nvidia.com>
Link: https://patch.msgid.link/20261014133632.3440297-1-nirmoyd@nvidia.com
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

diff --git a/drivers/iommu/iommufd/eventq.c b/drivers/iommu/iommufd/eventq.c
index 747dd5155121..b8a54454dd17 100644
--- a/drivers/iommu/iommufd/eventq.c
+++ b/drivers/iommu/iommufd/eventq.c
@@ -396,9 +396,11 @@ static __poll_t iommufd_eventq_fops_poll(struct file *filep,
 static int iommufd_eventq_fops_release(struct inode *inode, struct file *filep)
 {
 	struct iommufd_eventq *eventq = filep->private_data;
+	/* eventq may be freed once the users reference is dropped. */
+	struct iommufd_ctx *ictx = eventq->ictx;
 
 	refcount_dec(&eventq->obj.users);
-	iommufd_ctx_put(eventq->ictx);
+	iommufd_ctx_put(ictx);
 	return 0;
 }