UBI: try to reveal buggy MTD drivers (276832d8) · Commits · 戴 / test

When reading data from the flash, corrupt the buffer we are about to read to. The idea is to fix the following possible situation: 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 use 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. Thus, try to reveal such buggy MTD drivers with simple debugging code which fills the read buffer with 0x12 constant. Signed-off-by:

Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

drivers/mtd/ubi/io.c

+22 −0

Original line number	Diff line number	Diff line
		@@ -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);

Admin message