On Sun, Oct 14, 2007 at 10:15:42AM -0700, Casey Schaufler wrote:
> This version fixes a major blunder in label handling. The system
> works, but has a serious memory leak that also induces a gradual
> performance degradation. Al Viro gets the credit for pointing out
> that one. Al suggested several other improvements that are not
> included. They should come soon, but I wanted to get this flaw
> out of the code before too many people hit it.
Ahem... This
> +static ssize_t smk_write_doi(struct file *file, const char __user *buf,
> + size_t count, loff_t *ppos)
> +{
> + char temp[80];
> + int i;
> +
> + if (!capable(CAP_MAC_OVERRIDE))
> + return -EPERM;
> +
> + if (count > sizeof(temp))
> + return -EINVAL;
> +
> + if (copy_from_user(temp, buf, count) != 0)
> + return -EFAULT;
> +
> + if (sscanf(temp, "%d", &i) != 1)
> + return -EINVAL;
is not really a missing improvement; it's a geniune undefined behaviour.
temp[] is uninitialized, then you copy there some data that doesn't have
to contain NUL, then you call sscanf(). Boom. The same goes for the rest
of similar places.
And this
> +static ssize_t smk_read_ambient(struct file *filp, char __user *buf,
> + size_t cn, loff_t *ppos)
> +{
> + ssize_t rc;
> + int asize = strlen(smack_net_ambient) + 1;
> +
> + if (cn < asize)
> + return -EINVAL;
> +
> + if (*ppos != 0)
> + return 0;
> +
> + rc = simple_read_from_buffer(buf, cn, ppos, smack_net_ambient, asize);
is honest-to-$DEITY security hole - that file is world-readable and there's
nothing to prevent simple_read_from_buffer() blocking on page-in of buf,
then root writing to that file changing smack_net_ambient and doing kfree()
on the old value - one we'd already passed to simple_read_from_buffer().
At which point reader is about to get whatever data that might land in
whatever that memory gets reused for.
Besides, as I said the last time, smack_net_ambient has every right to
get changed between strlen() and passing argument to simple_read_from_buffer(),
in which case you'll be copying the amount of data that used to be in the
old one, taking it from the new one. New one might very well be shorter.
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