The patch titled
Subject: ipc/shm: call underlying open/close vm_ops
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
ipc-shm-call-underlying-open-close-vm_ops.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/ipc-shm-call-underlying-open-close-vm_ops.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Subject: ipc/shm: call underlying open/close vm_ops
Date: Wed, 9 Nov 2022 16:21:50 -0800
Shared memory segments can be created that are backed by hugetlb pages.
When this happens, the vmas associated with any mappings (shmat) are
marked VM_HUGETLB, yet the vm_ops for such mappings are provided by
ipc/shm (shm_vm_ops). There is a mechanism to call the underlying
hugetlb vm_ops, and this is done for most operations. However, it is
not done for open and close.
This was not an issue until the introduction of the hugetlb vma_lock.
This lock structure is pointed to by vm_private_data and the open/close
vm_ops help maintain this structure. The special hugetlb routine
called at fork took care of structure updates at fork time. However,
vma_splitting is not properly handled for ipc shared memory mappings
backed by hugetlb pages. This can result in a "kernel NULL pointer
dereference" BUG or use after free as two vmas point to the same lock
structure.
Update the shm open and close routines to always call the underlying
open and close routines.
Link: https://lkml.kernel.org/r/20221110002150.440055-1-mike.kravetz@xxxxxxxxxx
Fixes: 8d9bfb260814 ("hugetlb: add vma based lock for pmd sharing")
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Reported-by: Doug Nelson <doug.nelson@xxxxxxxxx>
Cc: Alexander Mikhalitsyn <alexander.mikhalitsyn@xxxxxxxxxxxxx>
Cc: "Eric W . Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
ipc/shm.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
--- a/ipc/shm.c~ipc-shm-call-underlying-open-close-vm_ops
+++ a/ipc/shm.c
@@ -302,7 +302,15 @@ static int __shm_open(struct vm_area_str
/* This is called by fork, once for every shm attach. */
static void shm_open(struct vm_area_struct *vma)
{
- int err = __shm_open(vma);
+ struct file *file = vma->vm_file;
+ struct shm_file_data *sfd = shm_file_data(file);
+ int err;
+
+ /* Always call underlying open if present */
+ if (sfd->vm_ops->open)
+ sfd->vm_ops->open(vma);
+
+ err = __shm_open(vma);
/*
* We raced in the idr lookup or with shm_destroy().
* Either way, the ID is busted.
@@ -366,6 +374,10 @@ static void shm_close(struct vm_area_str
struct shmid_kernel *shp;
struct ipc_namespace *ns = sfd->ns;
+ /* Always call underlying close if present */
+ if (sfd->vm_ops->close)
+ sfd->vm_ops->close(vma);
+
down_write(&shm_ids(ns).rwsem);
/* remove from the list of attaches of the shm segment */
shp = shm_lock(ns, sfd->id);
_
Patches currently in -mm which might be from mike.kravetz@xxxxxxxxxx are
ipc-shm-call-underlying-open-close-vm_ops.patch
hugetlb-dont-delete-vma_lock-in-hugetlb-madv_dontneed-processing.patch
selftests-vm-update-hugetlb-madvise.patch
