Messages in this thread | | | From | Kees Cook <> | Date | Sat, 25 Aug 2018 23:19:30 -0700 | Subject | Re: [PATCH] net: sched: Fix memory exposure from short TCA_U32_SEL |
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On Sat, Aug 25, 2018 at 11:15 PM, Al Viro <viro@zeniv.linux.org.uk> wrote: > On Sat, Aug 25, 2018 at 10:58:01PM -0700, Kees Cook wrote: >> Via u32_change(), TCA_U32_SEL has an unspecified type in the netlink >> policy, so max length isn't enforced, only minimum. This means nkeys >> (from userspace) was being trusted without checking the actual size of >> nla_len(), which could lead to a memory over-read, and ultimately an >> exposure via a call to u32_dump(). Reachability is CAP_NET_ADMIN within >> a namespace. >> >> Reported-by: Al Viro <viro@zeniv.linux.org.uk> >> Cc: Jamal Hadi Salim <jhs@mojatatu.com> >> Cc: Cong Wang <xiyou.wangcong@gmail.com> >> Cc: Jiri Pirko <jiri@resnulli.us> >> Cc: "David S. Miller" <davem@davemloft.net> >> Cc: netdev@vger.kernel.org >> Signed-off-by: Kees Cook <keescook@chromium.org> >> --- >> This should go through -stable please, but I have left off the "Cc: >> stable" as per netdev patch policy. Note that use of struct_size() >> will need manual expansion in backports, such as: >> sel_size = sizeof(*s) + sizeof(*s->keys) * s->nkeys; > > Saner approach would be sel_size = offsetof(struct tc_u32_sel, keys[s->nkeys])...
Either is fine by me.
>> + sel_size = struct_size(s, keys, s->nkeys); >> + if (nla_len(tb[TCA_U32_SEL]) < sel_size) { >> + err = -EINVAL; >> + goto erridr; >> + } >> >> - n = kzalloc(sizeof(*n) + s->nkeys*sizeof(struct tc_u32_key), GFP_KERNEL); >> + n = kzalloc(offsetof(typeof(*n), sel) + sel_size, GFP_KERNEL); > > ITYM > n = kzalloc(offsetof(struct tc_u_common, sel.keys[s->nkeys]), GFP_KERNEL);
I prefer to reuse sel_size and keep typeof() to keep things tied to "n" more directly. *shrug*
-Kees
-- Kees Cook Pixel Security
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