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@arista.com
Fixes: commit e346b38 ("mm/mremap: add MREMAP_DONTUNMAP to mremap()")
Signed-off-by: Dmitry Safonov <dima@arista.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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;

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);

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);

mm/mmap.c

@@ -3405,10 +3405,14 @@ 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;
 

mm/mremap.c

@@ -534,7 +534,7 @@ 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)) {