libfec: fix back-up header validation

If the primary fec_header is invalid, correctly validate the
back-up header even if it's not at the beginning of a block.

Change-Id: Ida15e6eeb08f3d50d4e096897ccc814c0949e8f8

1 files changed, 3 insertions, 0 deletions

diff --git a/libfec/fec_open.cpp b/libfec/fec_open.cpp
index 1923406f..c1d4afdb 100644
--- a/libfec/fec_open.cpp
+++ b/libfec/fec_open.cpp
@@ -117,6 +117,9 @@ static int parse_ecc_header(fec_handle *f, uint64_t offset)
         return -1;
     }
 
+    /* move offset back to the beginning of the block for validating header */
+    offset -= offset % FEC_BLOCKSIZE;
+
     if (header.magic != FEC_MAGIC) {
         return -1;
     }