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A caller that pre-sets result to a non-zero value can suppress that correction, leaving pos advanced past the last valid entry; the (partially out-of-bounds) fmt_buffer[pos] fields are then copied back to userspace, leaking heap contents. Only expect is an Input field; copy just that member in and zero the rest of cdata. Fixes: 8fd575200db5 ("s390/dasd: Add new ioctl BIODASDCHECKFMT") Reported-by: Sashiko Closes: https://sashiko.dev/#/patchset/20260722103704.1709668-1-sth@linux.ibm.com Cc: stable@vger.kernel.org #4.7 Reviewed-by: Jan Höppner Signed-off-by: Stefan Haberland --- drivers/s390/block/dasd_ioctl.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/s390/block/dasd_ioctl.c b/drivers/s390/block/dasd_ioctl.c index e5b8b413f5ab..2f2ec2bea333 100644 --- a/drivers/s390/block/dasd_ioctl.c +++ b/drivers/s390/block/dasd_ioctl.c @@ -303,7 +303,9 @@ static int dasd_ioctl_check_format(struct block_device *bdev, void __user *argp) goto out_err; } - if (copy_from_user(&cdata, argp, sizeof(cdata))) { + /* copy only input fields, clear the rest */ + memset(&cdata, 0, sizeof(cdata)); + if (copy_from_user(&cdata.expect, argp, sizeof(cdata.expect))) { rc = -EFAULT; goto out_err; } -- 2.53.0