1 files changed, 22 insertions, 0 deletions

diff --git a/drivers/mtd/ubi/io.c b/drivers/mtd/ubi/io.c
index 65915a649861..339a74f11c0b 100644
--- a/drivers/mtd/ubi/io.c
+++ b/drivers/mtd/ubi/io.c
@@ -146,6 +146,28 @@ int ubi_io_read(const struct ubi_device *ubi, void *buf, int pnum, int offset,
         if (err)
                 return err;
 
+        /*
+         * Deliberately corrupt the buffer to improve robustness. Indeed, if we
+         * do not do this, the following may happen:
+         * 1. The buffer contains data from previous operation, e.g., read from
+         *    another PEB previously. The data looks like expected, e.g., if we
+         *    just do not read anything and return - the caller would not
+         *    notice this. E.g., if we are reading a VID header, the buffer may
+         *    contain a valid VID header from another PEB.
+         * 2. The driver is buggy and returns us success or -EBADMSG or
+         *    -EUCLEAN, but it does not actually put any data to the buffer.
+         *
+         * This may confuse UBI or upper layers - they may think the buffer
+         * contains valid data while in fact it is just old data. This is
+         * especially possible because UBI (and UBIFS) relies on CRC, and
+         * treats data as correct even in case of ECC errors if the CRC is
+         * correct.
+         *
+         * Try to prevent this situation by changing the first byte of the
+         * buffer.
+         */
+        *((uint8_t *)buf) ^= 0xFF;
+
         addr = (loff_t)pnum * ubi->peb_size + offset;
 retry:
         err = ubi->mtd->read(ubi->mtd, addr, len, &read, buf);