1 files changed, 53 insertions, 0 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 44361928bbb0..aac71aef4c61 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3056,6 +3056,59 @@ int generic_file_rw_checks(struct file *file_in, struct file *file_out)
         return 0;
 }
 
+/*
+ * Performs necessary checks before doing a file copy
+ *
+ * Can adjust amount of bytes to copy via @req_count argument.
+ * Returns appropriate error code that caller should return or
+ * zero in case the copy should be allowed.
+ */
+int generic_copy_file_checks(struct file *file_in, loff_t pos_in,
+                             struct file *file_out, loff_t pos_out,
+                             size_t *req_count, unsigned int flags)
+{
+        struct inode *inode_in = file_inode(file_in);
+        struct inode *inode_out = file_inode(file_out);
+        uint64_t count = *req_count;
+        loff_t size_in;
+        int ret;
+
+        ret = generic_file_rw_checks(file_in, file_out);
+        if (ret)
+                return ret;
+
+        /* Don't touch certain kinds of inodes */
+        if (IS_IMMUTABLE(inode_out))
+                return -EPERM;
+
+        if (IS_SWAPFILE(inode_in) || IS_SWAPFILE(inode_out))
+                return -ETXTBSY;
+
+        /* Ensure offsets don't wrap. */
+        if (pos_in + count < pos_in || pos_out + count < pos_out)
+                return -EOVERFLOW;
+
+        /* Shorten the copy to EOF */
+        size_in = i_size_read(inode_in);
+        if (pos_in >= size_in)
+                count = 0;
+        else
+                count = min(count, size_in - (uint64_t)pos_in);
+
+        ret = generic_write_check_limits(file_out, pos_out, &count);
+        if (ret)
+                return ret;
+
+        /* Don't allow overlapped copying within the same file. */
+        if (inode_in == inode_out &&
+            pos_out + count > pos_in &&
+            pos_out < pos_in + count)
+                return -EINVAL;
+
+        *req_count = count;
+        return 0;
+}
+
 int pagecache_write_begin(struct file *file, struct address_space *mapping,
                                 loff_t pos, unsigned len, unsigned flags,
                                 struct page **pagep, void **fsdata)