Messages in this thread | | | Date | Tue, 11 May 2021 23:17:35 +0100 | From | Phillip Potter <> | Subject | Re: [PATCH] netlink: netlink_sendmsg: memset unused tail bytes in skb |
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On Sun, May 09, 2021 at 03:10:51PM +0200, Florian Westphal wrote: > Phillip Potter <phil@philpotter.co.uk> wrote: > > When allocating the skb within netlink_sendmsg, with certain supplied > > len arguments, extra bytes are allocated at the end of the data buffer, > > due to SKB_DATA_ALIGN giving a larger size within __alloc_skb for > > alignment reasons. This means that after using skb_put with the same > > len value and then copying data into the skb, the skb tail area is > > non-zero in size and contains uninitialised bytes. Wiping this area > > (if it exists) fixes a KMSAN-found uninit-value bug reported by syzbot at: > > https://syzkaller.appspot.com/bug?id=3e63bcec536b7136b54c72e06adeb87dc6519f69 > > This patch papers over the real bug. > > Please fix TIPC instead. > Incomplete patch as a starting point: > > diff --git a/net/tipc/node.c b/net/tipc/node.c > --- a/net/tipc/node.c > +++ b/net/tipc/node.c > @@ -2481,7 +2481,6 @@ int tipc_nl_node_get_link(struct sk_buff *skb, struct genl_info *info) > struct net *net = genl_info_net(info); > struct nlattr *attrs[TIPC_NLA_LINK_MAX + 1]; > struct tipc_nl_msg msg; > - char *name; > int err; > > msg.portid = info->snd_portid; > @@ -2499,13 +2498,11 @@ int tipc_nl_node_get_link(struct sk_buff *skb, struct genl_info *info) > if (!attrs[TIPC_NLA_LINK_NAME]) > return -EINVAL; > > - name = nla_data(attrs[TIPC_NLA_LINK_NAME]); > - > msg.skb = nlmsg_new(NLMSG_GOODSIZE, GFP_KERNEL); > if (!msg.skb) > return -ENOMEM; > > - if (strcmp(name, tipc_bclink_name) == 0) { > + if (nla_strcmp(attrs[TIPC_NLA_LINK_NAME], tipc_bclink_name) == 0) { > err = tipc_nl_add_bc_link(net, &msg, tipc_net(net)->bcl); > if (err) > goto err_free; > > > You will also need to change tipc_node_find_by_name() to pass the nla > attr. > > Alternatively TIPC_NLA_LINK_NAME policy can be changed: > > diff --git a/net/tipc/netlink.c b/net/tipc/netlink.c > --- a/net/tipc/netlink.c > +++ b/net/tipc/netlink.c > @@ -88,7 +88,7 @@ const struct nla_policy tipc_nl_net_policy[TIPC_NLA_NET_MAX + 1] = { > > const struct nla_policy tipc_nl_link_policy[TIPC_NLA_LINK_MAX + 1] = { > [TIPC_NLA_LINK_UNSPEC] = { .type = NLA_UNSPEC }, > - [TIPC_NLA_LINK_NAME] = { .type = NLA_STRING, > + [TIPC_NLA_LINK_NAME] = { .type = NLA_NUL_STRING, > > > ... which makes it safe to treat the raw attribute payload as a c-string, > but this might break existing userspace applications. > > Its probably a good idea to audit all NLA_STRING attributes in tipc for > similar problems.
Dear Florian,
Thank you for your feedback and code + suggestions, I will take a look at this over the next few days and then resubmit.
Regards, Phil
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