FAILED: patch "[PATCH] VMCI: fix race between vmci_host_setup_notify and" failed to apply to 5.4-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.4-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-5.4.y
git checkout FETCH_HEAD
git cherry-pick -x 1bd6406fb5f36c2bb1e96e27d4c3e9f4d09edde4
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025061722-shaded-throwback-5dda@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

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

From 1bd6406fb5f36c2bb1e96e27d4c3e9f4d09edde4 Mon Sep 17 00:00:00 2001
From: Wupeng Ma <mawupeng1@huawei.com>
Date: Sat, 10 May 2025 11:30:40 +0800
Subject: [PATCH] VMCI: fix race between vmci_host_setup_notify and
 vmci_ctx_unset_notify

During our test, it is found that a warning can be trigger in try_grab_folio
as follow:

  ------------[ cut here ]------------
  WARNING: CPU: 0 PID: 1678 at mm/gup.c:147 try_grab_folio+0x106/0x130
  Modules linked in:
  CPU: 0 UID: 0 PID: 1678 Comm: syz.3.31 Not tainted 6.15.0-rc5 #163 PREEMPT(undef)
  RIP: 0010:try_grab_folio+0x106/0x130
  Call Trace:
   <TASK>
   follow_huge_pmd+0x240/0x8e0
   follow_pmd_mask.constprop.0.isra.0+0x40b/0x5c0
   follow_pud_mask.constprop.0.isra.0+0x14a/0x170
   follow_page_mask+0x1c2/0x1f0
   __get_user_pages+0x176/0x950
   __gup_longterm_locked+0x15b/0x1060
   ? gup_fast+0x120/0x1f0
   gup_fast_fallback+0x17e/0x230
   get_user_pages_fast+0x5f/0x80
   vmci_host_unlocked_ioctl+0x21c/0xf80
  RIP: 0033:0x54d2cd
  ---[ end trace 0000000000000000 ]---

Digging into the source, context->notify_page may init by get_user_pages_fast
and can be seen in vmci_ctx_unset_notify which will try to put_page. However
get_user_pages_fast is not finished here and lead to following
try_grab_folio warning. The race condition is shown as follow:

cpu0			cpu1
vmci_host_do_set_notify
vmci_host_setup_notify
get_user_pages_fast(uva, 1, FOLL_WRITE, &context->notify_page);
lockless_pages_from_mm
gup_pgd_range
gup_huge_pmd  // update &context->notify_page
			vmci_host_do_set_notify
			vmci_ctx_unset_notify
			notify_page = context->notify_page;
			if (notify_page)
			put_page(notify_page);	// page is freed
__gup_longterm_locked
__get_user_pages
follow_trans_huge_pmd
try_grab_folio // warn here

To slove this, use local variable page to make notify_page can be seen
after finish get_user_pages_fast.

Fixes: a1d88436d53a ("VMCI: Fix two UVA mapping bugs")
Cc: stable <stable@kernel.org>
Closes: https://lore.kernel.org/all/e91da589-ad57-3969-d979-879bbd10dddd@huawei.com/
Signed-off-by: Wupeng Ma <mawupeng1@huawei.com>
Link: https://lore.kernel.org/r/20250510033040.901582-1-mawupeng1@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/misc/vmw_vmci/vmci_host.c b/drivers/misc/vmw_vmci/vmci_host.c
index abe79f6fd2a7..b64944367ac5 100644
--- a/drivers/misc/vmw_vmci/vmci_host.c
+++ b/drivers/misc/vmw_vmci/vmci_host.c
@@ -227,6 +227,7 @@ static int drv_cp_harray_to_user(void __user *user_buf_uva,
 static int vmci_host_setup_notify(struct vmci_ctx *context,
 				  unsigned long uva)
 {
+	struct page *page;
 	int retval;
 
 	if (context->notify_page) {
@@ -243,13 +244,11 @@ static int vmci_host_setup_notify(struct vmci_ctx *context,
 	/*
 	 * Lock physical page backing a given user VA.
 	 */
-	retval = get_user_pages_fast(uva, 1, FOLL_WRITE, &context->notify_page);
-	if (retval != 1) {
-		context->notify_page = NULL;
+	retval = get_user_pages_fast(uva, 1, FOLL_WRITE, &page);
+	if (retval != 1)
 		return VMCI_ERROR_GENERIC;
-	}
-	if (context->notify_page == NULL)
-		return VMCI_ERROR_UNAVAILABLE;
+
+	context->notify_page = page;
 
 	/*
 	 * Map the locked page and set up notify pointer.