[PATCH v2 1/2] scsi: scsi_debug: scsi: scsi_debug: fix some bugs in sdebug_error_write()

[Dan Carpenter <dan.carpenter@linaro.org>]

There are two bug in this code:
1) If count is zero, then it will lead to a NULL dereference.  The
   kmalloc() will successfully allocate zero bytes and the test for
   "if (buf[0] == '-')" will read beyond the end of the zero size buffer
   and Oops.
2) The code does not ensure that the user's string is properly NUL
   terminated which could lead to a read overflow.

Fixes: a9996d722b11 ("scsi: scsi_debug: Add interface to manage error injection for a single device")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
---
v2: At first I tried to use strndup_user() but that only accepts NUL
    terminated strings and the user string is normally not terminated.

 drivers/scsi/scsi_debug.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index 67922e2c4c19..0dd21598f7b6 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -1019,7 +1019,7 @@ static ssize_t sdebug_error_write(struct file *file, const char __user *ubuf,
 	struct sdebug_err_inject *inject;
 	struct scsi_device *sdev = (struct scsi_device *)file->f_inode->i_private;
 
-	buf = kmalloc(count, GFP_KERNEL);
+	buf = kzalloc(count + 1, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
 
-- 
2.42.0