mm/mmap: fix memory leak in mmap_region()

There is a memory leak reported by kmemleak:

unreferenced object 0xffff88817231ce40 (size 224):
comm "mount.cifs", pid 19308, jiffies 4295917571 (age 405.880s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
60 c0 b2 00 81 88 ff ff 98 83 01 42 81 88 ff ff `..........B....
backtrace:
[<ffffffff81936171>] __alloc_file+0x21/0x250
[<ffffffff81937051>] alloc_empty_file+0x41/0xf0
[<ffffffff81937159>] alloc_file+0x59/0x710
[<ffffffff81937964>] alloc_file_pseudo+0x154/0x210
[<ffffffff81741dbf>] __shmem_file_setup+0xff/0x2a0
[<ffffffff817502cd>] shmem_zero_setup+0x8d/0x160
[<ffffffff817cc1d5>] mmap_region+0x1075/0x19d0
[<ffffffff817cd257>] do_mmap+0x727/0x1110
[<ffffffff817518b2>] vm_mmap_pgoff+0x112/0x1e0
[<ffffffff83adf955>] do_syscall_64+0x35/0x80
[<ffffffff83c0006a>] entry_SYSCALL_64_after_hwframe+0x46/0xb0

The root cause was traced to an error handing path in mmap_region() when
arch_validate_flags() or mas_preallocate() fails. In the shared anonymous
mapping sence, vma will be setuped and mapped with a new shared anonymous
file via shmem_zero_setup(). So in this case, the file resource needs to
be released.

Fix it by calling fput(vma->vm_file) and unmap_region() when
arch_validate_flags() or mas_preallocate() returns an error in the shared
anonymous mapping sence.

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: d4af56c5c7c6 ("mm: start tracking VMAs with maple tree")
Fixes: c462ac288f2c ("mm: Introduce arch_validate_flags()")
Signed-off-by: Li Zetao <[e-mail]>
Reviewed-by: Liam R. Howlett <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

mm/mmap.c

···
 		error = -EINVAL;
 		if (file)
 			goto close_and_free_vma;
+		else if (vma->vm_file)
+			goto unmap_and_free_vma;
 		else
 			goto free_vma;
 	}
···
 		error = -ENOMEM;
 		if (file)
 			goto close_and_free_vma;
+		else if (vma->vm_file)
+			goto unmap_and_free_vma;
 		else
 			goto free_vma;
 	}
···
 
 	/* Undo any partial mapping done by a device driver. */
 	unmap_region(mm, mas.tree, vma, prev, next, vma->vm_start, vma->vm_end);
-	if (vm_flags & VM_SHARED)
+	if (file && (vm_flags & VM_SHARED))
 		mapping_unmap_writable(file->f_mapping);
 free_vma:
 	vm_area_free(vma);