eCryptfs: Infinite loop due to overflow in ecryptfs_write()

commit 684a3ff upstream.

ecryptfs_write() can enter an infinite loop when truncating a file to a
size larger than 4G. This only happens on architectures where size_t is
represented by 32 bits.

This was caused by a size_t overflow due to it incorrectly being used to
store the result of a calculation which uses potentially large values of
type loff_t.

[[email protected]: rewrite subject and commit message]
Signed-off-by: Li Wang <[email protected]>
Signed-off-by: Yunchuan Wen <[email protected]>
Reviewed-by: Cong Wang <[email protected]>
Signed-off-by: Tyler Hicks <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

fs/ecryptfs/read_write.c

@@ -134,7 +134,7 @@ int ecryptfs_write(struct file *ecryptfs_file, char *data, loff_t offset,
 		pgoff_t ecryptfs_page_idx = (pos >> PAGE_CACHE_SHIFT);
 		size_t start_offset_in_page = (pos & ~PAGE_CACHE_MASK);
 		size_t num_bytes = (PAGE_CACHE_SIZE - start_offset_in_page);
-		size_t total_remaining_bytes = ((offset + size) - pos);
+		loff_t total_remaining_bytes = ((offset + size) - pos);
 
 		if (fatal_signal_pending(current)) {
 			rc = -EINTR;
@@ -145,7 +145,7 @@ int ecryptfs_write(struct file *ecryptfs_file, char *data, loff_t offset,
 			num_bytes = total_remaining_bytes;
 		if (pos < offset) {
 			/* remaining zeros to write, up to destination offset */
-			size_t total_remaining_zeros = (offset - pos);
+			loff_t total_remaining_zeros = (offset - pos);
 
 			if (num_bytes > total_remaining_zeros)
 				num_bytes = total_remaining_zeros;