On Tue, 9 Oct 2012 15:54:01 -0700
Kees Cook <keesc...@chromium.org> wrote:
> Calling uname() with the UNAME26 personality set allows a leak of kernel
> stack contents. This fixes it by initializing the stack buffer to zero,
> defensively calculating the length of copy_to_user() call, and making
> the len argument unsigned.
>
> ...
>
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -1265,13 +1265,13 @@ DECLARE_RWSEM(uts_sem);
> * Work around broken programs that cannot handle "Linux 3.0".
> * Instead we map 3.x to 2.6.40+x, so e.g. 3.0 would be 2.6.40
> */
> -static int override_release(char __user *release, int len)
> +static int override_release(char __user *release, size_t len)
> {
> int ret = 0;
> - char buf[65];
>
> if (current->personality & UNAME26) {
> - char *rest = UTS_RELEASE;
> + const char *rest = UTS_RELEASE;
> + char buf[65] = { 0 };
> int ndots = 0;
> unsigned v;
>
> @@ -1283,7 +1283,9 @@ static int override_release(char __user *release, int
> len)
> rest++;
> }
> v = ((LINUX_VERSION_CODE >> 8) & 0xff) + 40;
> - snprintf(buf, len, "2.6.%u%s", v, rest);
> + snprintf(buf, sizeof(buf), "2.6.%u%s", v, rest);
> + if (sizeof(buf) < len)
> + len = sizeof(buf);
> ret = copy_to_user(release, buf, len);
> }
> return ret;
This looks unecessarily complicated. Is there a reason to be copying
all 65 bytes out to userspace?
If not, then couldn't we just do
len = scnprintf(...);
ret = copy_to_user(..., len + 1);
?
(This code is application #11,493 for the sprintf_user() which we don't have)
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
