[PATCH] mm: remap_file_pages: grab file ref to prevent race while mmaping

[Sasha Levin <sasha.levin@oracle.com>]

A file reference should be held while a file is mmaped, otherwise it might
be freed while being used.

Suggested-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
---
 mm/mmap.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/mmap.c b/mm/mmap.c
index 2a0e0a8..da3c212 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2593,6 +2593,7 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
 	struct vm_area_struct *vma;
 	unsigned long populate = 0;
 	unsigned long ret = -EINVAL;
+	struct file *file;
 
 	pr_warn_once("%s (%d) uses deprecated remap_file_pages() syscall. "
 			"See Documentation/vm/remap_file_pages.txt.\n",
@@ -2636,8 +2637,10 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
 		munlock_vma_pages_range(vma, start, start + size);
 	}
 
+	file = get_file(vma->vm_file);
 	ret = do_mmap_pgoff(vma->vm_file, start, size,
 			prot, flags, pgoff, &populate);
+	fput(file);
 out:
 	up_write(&mm->mmap_sem);
 	if (populate)
-- 
1.7.10.4

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