On 5/29/2015 8:49 AM, Borislav Petkov wrote:
On Wed, May 27, 2015 at 02:03:35PM -0500, Aravind Gopalakrishnan wrote:
+#define MAX_FLAG_OPT_SIZE 10
Why 10?
This should be 2 and increased when another, longer injection type
string gets introduced.
So I hit an issue when I have this as 2 and moving 'ret = cnt' statement
(in flags_write() below) to after the check for MAX_FLAG_OPT_SIZE.
The problem was, if I did echo hw > flags;
I would get an error on dmesg like so-
[ 78.692949] flags_write: Invalid flags value:
But the write would have actually gone through. i.e, if we do cat flags,
the output was 'hw'.
The issue seems to be that 'cnt' of flags_write() is 3 (after accounting
for a terminating NULL) when we enter the function (for this case),
Since we move 'ret = cnt;' statement to after the check, we end up
returning 2.
And since it is less than 'cnt', we re-enter flags_write() for the final
NULL character.
At this point, our comparisons with flags_options[] fail and we end up
returning -EINVAL from __set_inj().
Hence the error on dmesg..
The fix to this was simply having MAX_FLAG_OPT_SIZE as 3. In this case,
we already account for the NULL and flags_write()
returns the correct value upon success.
So I shall go ahead and make that change to MAX_FLAG_OPT_SIZE as 3 and
increase it in subsequent patch for the apic interrupts.
Thanks,
-Aravind.
-DEFINE_SIMPLE_ATTRIBUTE(flags_fops, flags_get, flags_set, "%llu\n");
+static ssize_t flags_write(struct file *filp, const char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ char buf[MAX_FLAG_OPT_SIZE + 1];
+ int err;
+ size_t ret;
+
+ ret = cnt;
You're assigning cnt to ret here...
+
+ if (cnt > MAX_FLAG_OPT_SIZE)
+ cnt = MAX_FLAG_OPT_SIZE;
... but correcting cnt afterwards. The assignment should be *after* that
correction.
+
+ if (copy_from_user(&buf, ubuf, cnt))
+ return -EFAULT;
+
+ buf[cnt] = 0;
+
+ /* strip whitespaces.. */
+ strstrip(buf);
+
+ err = __set_inj(buf, cnt - 1);
+ if (err) {
+ pr_err("%s: Invalid flags value: %s\n", __func__, buf);
+ return err;
+ }
+
+ *ppos += ret;
+
+ return ret;
+}
+
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
