This is a note to let you know that I've just added the patch titled
xen: privcmd: Fix possible access to a freed kirqfd instance
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
xen-privcmd-fix-possible-access-to-a-freed-kirqfd-in.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit f2e56ed216a0c300a28ddc6ebf584d1b4e6cc4fb
Author: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
Date: Tue Jun 18 15:12:29 2024 +0530
xen: privcmd: Fix possible access to a freed kirqfd instance
[ Upstream commit 611ff1b1ae989a7bcce3e2a8e132ee30e968c557 ]
Nothing prevents simultaneous ioctl calls to privcmd_irqfd_assign() and
privcmd_irqfd_deassign(). If that happens, it is possible that a kirqfd
created and added to the irqfds_list by privcmd_irqfd_assign() may get
removed by another thread executing privcmd_irqfd_deassign(), while the
former is still using it after dropping the locks.
This can lead to a situation where an already freed kirqfd instance may
be accessed and cause kernel oops.
Use SRCU locking to prevent the same, as is done for the KVM
implementation for irqfds.
Reported-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Suggested-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Link: https://lore.kernel.org/r/9e884af1f1f842eacbb7afc5672c8feb4dea7f3f.1718703669.git.viresh.kumar@xxxxxxxxxx
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index 923f064c7e3e..61aaded483e1 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -17,6 +17,7 @@
#include <linux/poll.h>
#include <linux/sched.h>
#include <linux/slab.h>
+#include <linux/srcu.h>
#include <linux/string.h>
#include <linux/workqueue.h>
#include <linux/errno.h>
@@ -842,6 +843,7 @@ static long privcmd_ioctl_mmap_resource(struct file *file,
/* Irqfd support */
static struct workqueue_struct *irqfd_cleanup_wq;
static DEFINE_SPINLOCK(irqfds_lock);
+DEFINE_STATIC_SRCU(irqfds_srcu);
static LIST_HEAD(irqfds_list);
struct privcmd_kernel_irqfd {
@@ -869,6 +871,9 @@ static void irqfd_shutdown(struct work_struct *work)
container_of(work, struct privcmd_kernel_irqfd, shutdown);
u64 cnt;
+ /* Make sure irqfd has been initialized in assign path */
+ synchronize_srcu(&irqfds_srcu);
+
eventfd_ctx_remove_wait_queue(kirqfd->eventfd, &kirqfd->wait, &cnt);
eventfd_ctx_put(kirqfd->eventfd);
kfree(kirqfd);
@@ -931,7 +936,7 @@ static int privcmd_irqfd_assign(struct privcmd_irqfd *irqfd)
__poll_t events;
struct fd f;
void *dm_op;
- int ret;
+ int ret, idx;
kirqfd = kzalloc(sizeof(*kirqfd) + irqfd->size, GFP_KERNEL);
if (!kirqfd)
@@ -977,6 +982,7 @@ static int privcmd_irqfd_assign(struct privcmd_irqfd *irqfd)
}
}
+ idx = srcu_read_lock(&irqfds_srcu);
list_add_tail(&kirqfd->list, &irqfds_list);
spin_unlock_irqrestore(&irqfds_lock, flags);
@@ -988,6 +994,8 @@ static int privcmd_irqfd_assign(struct privcmd_irqfd *irqfd)
if (events & EPOLLIN)
irqfd_inject(kirqfd);
+ srcu_read_unlock(&irqfds_srcu, idx);
+
/*
* Do not drop the file until the kirqfd is fully initialized, otherwise
* we might race against the EPOLLHUP.
