[PATCH 3/6] mremap: Don't allow MREMAP_DONTUNMAP on special_mappings and aio

[Dmitry Safonov]

As kernel expect to see only one of such mappings, any further
operations on the VMA-copy may be unexpected by the kernel.
Maybe it's being on the safe side, but there doesn't seem to be any
expected use-case for this, so restrict it now.

Fixes: commit e346b3813067 ("mm/mremap: add MREMAP_DONTUNMAP to mremap()")
Signed-off-by: Dmitry Safonov <d...@arista.com>
---
 arch/x86/kernel/cpu/resctrl/pseudo_lock.c | 2 +-
 fs/aio.c                                  | 5 ++++-
 include/linux/mm.h                        | 2 +-
 mm/mmap.c                                 | 6 +++++-
 mm/mremap.c                               | 2 +-
 5 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c 
b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
index 0daf2f1cf7a8..e916646adc69 100644
--- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
+++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
@@ -1458,7 +1458,7 @@ static int pseudo_lock_dev_release(struct inode *inode, 
struct file *filp)
        return 0;
 }
 
-static int pseudo_lock_dev_mremap(struct vm_area_struct *area)
+static int pseudo_lock_dev_mremap(struct vm_area_struct *area, unsigned long 
flags)
 {
        /* Not supported */
        return -EINVAL;
diff --git a/fs/aio.c b/fs/aio.c
index d5ec30385566..3be3c0f77548 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -324,13 +324,16 @@ static void aio_free_ring(struct kioctx *ctx)
        }
 }
 
-static int aio_ring_mremap(struct vm_area_struct *vma)
+static int aio_ring_mremap(struct vm_area_struct *vma, unsigned long flags)
 {
        struct file *file = vma->vm_file;
        struct mm_struct *mm = vma->vm_mm;
        struct kioctx_table *table;
        int i, res = -EINVAL;
 
+       if (flags & MREMAP_DONTUNMAP)
+               return -EINVAL;
+
        spin_lock(&mm->ioctx_lock);
        rcu_read_lock();
        table = rcu_dereference(mm->ioctx_table);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 16b799a0522c..fd51a4a1f722 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -550,7 +550,7 @@ struct vm_operations_struct {
        void (*open)(struct vm_area_struct * area);
        void (*close)(struct vm_area_struct * area);
        int (*split)(struct vm_area_struct * area, unsigned long addr);
-       int (*mremap)(struct vm_area_struct * area);
+       int (*mremap)(struct vm_area_struct *area, unsigned long flags);
        vm_fault_t (*fault)(struct vm_fault *vmf);
        vm_fault_t (*huge_fault)(struct vm_fault *vmf,
                        enum page_entry_size pe_size);
diff --git a/mm/mmap.c b/mm/mmap.c
index bdd19f5b994e..50f853b0ec39 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3372,10 +3372,14 @@ static const char *special_mapping_name(struct 
vm_area_struct *vma)
        return ((struct vm_special_mapping *)vma->vm_private_data)->name;
 }
 
-static int special_mapping_mremap(struct vm_area_struct *new_vma)
+static int special_mapping_mremap(struct vm_area_struct *new_vma,
+                                 unsigned long flags)
 {
        struct vm_special_mapping *sm = new_vma->vm_private_data;
 
+       if (flags & MREMAP_DONTUNMAP)
+               return -EINVAL;
+
        if (WARN_ON_ONCE(current->mm != new_vma->vm_mm))
                return -EFAULT;
 
diff --git a/mm/mremap.c b/mm/mremap.c
index c248f9a52125..898e9818ba6d 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -384,7 +384,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
        if (moved_len < old_len) {
                err = -ENOMEM;
        } else if (vma->vm_ops && vma->vm_ops->mremap) {
-               err = vma->vm_ops->mremap(new_vma);
+               err = vma->vm_ops->mremap(new_vma, flags);
        }
 
        if (unlikely(err)) {
-- 
2.28.0