linux-kernel - [PATCH] VMCI: fix race between vmci_host_setup_notify and vmci_ctx_unset

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Message-ID: <20250510033040.901582-1-mawupeng1@huawei.com>
Date: Sat, 10 May 2025 11:30:40 +0800
From: Wupeng Ma <mawupeng1@...wei.com>
To: <bryan-bt.tan@...adcom.com>, <vishnu.dasa@...adcom.com>,
	<ryan.roberts@....com>, <jhansen@...are.com>, <darius@...are.com>,
	<acking@...are.com>
CC: <bcm-kernel-feedback-list@...adcom.com>, <gregkh@...uxfoundation.org>,
	<linux-kernel@...r.kernel.org>, <mawupeng1@...wei.com>,
	<sunnanyong@...wei.com>
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")
Closes: https://lore.kernel.org/all/e91da589-ad57-3969-d979-879bbd10dddd@huawei.com/
Signed-off-by: Wupeng Ma <mawupeng1@...wei.com>
---
 drivers/misc/vmw_vmci/vmci_host.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

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.
-- 
2.43.0