Oops with mtd_dataflash driver in 3.3

Will Newton will.newton at gmail.com
Fri Mar 30 06:51:02 EDT 2012

Hi all,

I'm seeing an oops in mtd_dataflash.c with Linux 3.3. What appears to
be happening is that otp_select_filemode calls mtd_read_fact_prot_reg
with -1 for offset and length and a NULL buffer to test if OTP
operations are supported. This finds its way down to otp_read in
mtd_dataflash.c and causes an oops when memcpying the returned data
into the NULL buf.

None of the checks in otp_read catches the negative length and offset.
Changing the length of the dummy read to 0 prevents the oops, but I'm
not sure if it is the preferred solution. Would this change be

diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index 50c6a1e..853744d 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -369,7 +369,7 @@ static int otp_select_filemode(struct
mtd_file_info *mfi, int mode)
         * Make a fake call to mtd_read_fact_prot_reg() to check if OTP
         * operations are supported.
-       if (mtd_read_fact_prot_reg(mtd, -1, -1, &retlen, NULL) == -EOPNOTSUPP)
+       if (mtd_read_fact_prot_reg(mtd, -1, 0, &retlen, NULL) == -EOPNOTSUPP)
                return -EOPNOTSUPP;

        switch (mode) {


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