On Thu, Oct 25, 2012 at 04:05:05PM -0700, Thomas Pedersen wrote:
> On Fri, Oct 26, 2012 at 12:46:39AM +0200, Johannes Berg wrote:
> > From: Johannes Berg <johannes.berg@xxxxxxxxx>
> >
> > A number of places in the mesh code don't check that
> > the frame data is present and in the skb header when
> > trying to access. Add those checks and the necessary
> > pskb_may_pull() calls. This prevents accessing data
> > that doesn't actually exist.
> >
> > To do this, export ieee80211_get_mesh_hdrlen() to be
> > able to use it in mac80211.
> >
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
> > ---
> > include/net/cfg80211.h | 9 +++++++++
> > net/mac80211/rx.c | 43 +++++++++++++++++++++++++++++++++++++++----
> > net/wireless/util.c | 3 ++-
> > 3 files changed, 50 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
> > index f8cd4cf..7d5b600 100644
> > --- a/include/net/cfg80211.h
> > +++ b/include/net/cfg80211.h
> > @@ -2652,6 +2652,15 @@ unsigned int ieee80211_get_hdrlen_from_skb(const struct sk_buff *skb);
> > unsigned int __attribute_const__ ieee80211_hdrlen(__le16 fc);
> >
> > /**
> > + * ieee80211_get_mesh_hdrlen - get mesh extension header length
> > + * @meshhdr: the mesh extension header, only the flags field
> > + * (first byte) will be accessed
> > + * Returns the length of the extension header, which is always at
> > + * least 6 bytes and at most 18 if address 5 and 6 are present.
> > + */
> > +unsigned int ieee80211_get_mesh_hdrlen(struct ieee80211s_hdr *meshhdr);
> > +
> > +/**
> > * DOC: Data path helpers
> > *
> > * In addition to generic utilities, cfg80211 also offers
> > diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
> > index 99cdee1..6d1fd39 100644
> > --- a/net/mac80211/rx.c
> > +++ b/net/mac80211/rx.c
> > @@ -531,6 +531,11 @@ ieee80211_rx_mesh_check(struct ieee80211_rx_data *rx)
> >
> > if (ieee80211_is_action(hdr->frame_control)) {
> > u8 category;
> > +
> > + /* make sure category field is present */
> > + if (rx->skb->len < IEEE80211_MIN_ACTION_SIZE)
> > + return RX_DROP_MONITOR;
> > +
> > mgmt = (struct ieee80211_mgmt *)hdr;
> > category = mgmt->u.action.category;
> > if (category != WLAN_CATEGORY_MESH_ACTION &&
> > @@ -1892,6 +1897,20 @@ ieee80211_rx_h_mesh_fwding(struct ieee80211_rx_data *rx)
> >
> > hdr = (struct ieee80211_hdr *) skb->data;
> > hdrlen = ieee80211_hdrlen(hdr->frame_control);
> > +
> > + /* make sure fixed part of mesh header is there, also checks skb len */
> > + if (!pskb_may_pull(rx->skb, hdrlen + 6))
> > + return RX_DROP_MONITOR;
> > +
> > + mesh_hdr = (struct ieee80211s_hdr *) (skb->data + hdrlen);
> > +
> > + /* make sure full mesh header is there, also checks skb len */
> > + if (!pskb_may_pull(rx->skb,
> > + hdrlen + ieee80211_get_mesh_hdrlen(mesh_hdr)))
> > + return RX_DROP_MONITOR;
> > +
> > + /* reload pointers */
> > + hdr = (struct ieee80211_hdr *) skb->data;
> > mesh_hdr = (struct ieee80211s_hdr *) (skb->data + hdrlen);
> >
> > /* frame is in RMC, don't forward */
> > @@ -1913,11 +1932,19 @@ ieee80211_rx_h_mesh_fwding(struct ieee80211_rx_data *rx)
> > char *mpp_addr;
> >
> > if (is_multicast_ether_addr(hdr->addr1)) {
> > - mpp_addr = hdr->addr3;
> > - proxied_addr = mesh_hdr->eaddr1;
> > + if (mesh_hdr->flags & MESH_FLAGS_AE_A4) {
> > + mpp_addr = hdr->addr3;
> > + proxied_addr = mesh_hdr->eaddr1;
> > + } else {
> > + return RX_DROP_MONITOR;
> > + }
> > } else {
> > - mpp_addr = hdr->addr4;
> > - proxied_addr = mesh_hdr->eaddr2;
> > + if (mesh_hdr->flags & MESH_FLAGS_AE_A5_A6) {
> > + mpp_addr = hdr->addr4;
> > + proxied_addr = mesh_hdr->eaddr2;
> > + } else {
> > + return RX_DROP_MONITOR;
> > + }
>
> This will drop all non-proxied mcast or unicast data frames :)
>
> It looks like this was already incorrect, but what if you only read the
> eaddrs if the right flag is set? Like:
>
> if (is_multicast_ether_addr(hdr->addr1) &&
> mesh_hdr->flags & MESH_FLAGS_AE_A4) {
> mpp_addr = hdr->addr3;
> proxied_addr = mesh_hdr->eaddr1;
> } else if (mesh_hdr->flags & MESH_FLAGS_AE_A5_A6) {
> mpp_addr = hdr->addr4;
> proxied_addr = mesh_hdr->eaddr2;
> }
Or even just:
if (mesh_hdr->flags & MESH_FLAGS_AE_A4) {
mpp_addr = hdr->addr3;
proxied_addr = mesh_hdr->eaddr1;
} else if (mesh_hdr->flags & MESH_FLAGS_AE_A5_A6) {
mpp_addr = hdr->addr4;
proxied_addr = mesh_hdr->eaddr2;
}
Should be sufficient since according to table 8-14, those bits are only
used for proxied mcast and unicast data frames, respectively.
Thomas
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