[patch 086/200] mremap: don't allow MREMAP_DONTUNMAP on special_mappings and aio

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From: Dmitry Safonov <dima@xxxxxxxxxx>
Subject: mremap: don't allow MREMAP_DONTUNMAP on special_mappings and aio

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.

Link: https://lkml.kernel.org/r/20201013013416.390574-4-dima@xxxxxxxxxx
Fixes: commit e346b3813067 ("mm/mremap: add MREMAP_DONTUNMAP to mremap()")
Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Brian Geffon <bgeffon@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxx>
Cc: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 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(-)

--- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c~mremap-dont-allow-mremap_dontunmap-on-special_mappings-and-aio
+++ a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
@@ -1458,7 +1458,7 @@ static int pseudo_lock_dev_release(struc
 	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;
--- a/fs/aio.c~mremap-dont-allow-mremap_dontunmap-on-special_mappings-and-aio
+++ a/fs/aio.c
@@ -324,13 +324,16 @@ static void aio_free_ring(struct kioctx
 	}
 }
 
-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);
--- a/include/linux/mm.h~mremap-dont-allow-mremap_dontunmap-on-special_mappings-and-aio
+++ a/include/linux/mm.h
@@ -558,7 +558,7 @@ 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);
--- a/mm/mmap.c~mremap-dont-allow-mremap_dontunmap-on-special_mappings-and-aio
+++ a/mm/mmap.c
@@ -3405,10 +3405,14 @@ static const char *special_mapping_name(
 	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;
 
--- a/mm/mremap.c~mremap-dont-allow-mremap_dontunmap-on-special_mappings-and-aio
+++ a/mm/mremap.c
@@ -534,7 +534,7 @@ static unsigned long move_vma(struct vm_
 	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)) {
_




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