Hi
On Fri, Nov 13, 2015 at 3:20 PM, Dan Carpenter <[email protected]> wrote:
> This condition doesn't work when len is smaller than expected and not a
> multiple of 4. In that situation "len - pos" is negative and type
> promoted to a high unsigned value and we do not break out of the loop.
> It causes the program calling it to crash.
Could you give an example how this can happen? The loop-invariant
should be "len >= pos", as such, this shouldn't happen. "pos" starts
out as 0, "len" is guaranteed to be >=0. "pos" is only incremented by
4, if "len - pos >= 4".
What am I missing?
Thanks
David
> Fixes: b42be38b2778 ('netlink: add API to retrieve all group memberships')
> Signed-off-by: Dan Carpenter <[email protected]>
>
> diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
> index 59651af..76a8466 100644
> --- a/net/netlink/af_netlink.c
> +++ b/net/netlink/af_netlink.c
> @@ -2373,7 +2373,7 @@ static int netlink_getsockopt(struct socket *sock, int
> level, int optname,
> err = 0;
> netlink_lock_table();
> for (pos = 0; pos * 8 < nlk->ngroups; pos += sizeof(u32)) {
> - if (len - pos < sizeof(u32))
> + if (len < pos + sizeof(u32))
> break;
>
> idx = pos / sizeof(unsigned long);
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