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authorStefano Brivio <sbrivio@redhat.com>2018-12-06 19:30:37 +0100
committerDavid S. Miller <davem@davemloft.net>2018-12-07 16:24:40 -0800
commite6ac64d4c4d095085d7dd71cbd05704ac99829b2 (patch)
tree9b93e099315cb036f69df1d45cac0e98de166976
parent66033f47ca60294a95fc85ec3a3cc909dab7b765 (diff)
downloadlinux-stericsson-e6ac64d4c4d095085d7dd71cbd05704ac99829b2.tar.gz
neighbour: Avoid writing before skb->head in neigh_hh_output()
While skb_push() makes the kernel panic if the skb headroom is less than the unaligned hardware header size, it will proceed normally in case we copy more than that because of alignment, and we'll silently corrupt adjacent slabs. In the case fixed by the previous patch, "ipv6: Check available headroom in ip6_xmit() even without options", we end up in neigh_hh_output() with 14 bytes headroom, 14 bytes hardware header and write 16 bytes, starting 2 bytes before the allocated buffer. Always check we're not writing before skb->head and, if the headroom is not enough, warn and drop the packet. v2: - instead of panicking with BUG_ON(), WARN_ON_ONCE() and drop the packet (Eric Dumazet) - if we avoid the panic, though, we need to explicitly check the headroom before the memcpy(), otherwise we'll have corrupted slabs on a running kernel, after we warn - use __skb_push() instead of skb_push(), as the headroom check is already implemented here explicitly (Eric Dumazet) Signed-off-by: Stefano Brivio <sbrivio@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--include/net/neighbour.h28
1 files changed, 23 insertions, 5 deletions
diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index f58b384aa6c9..665990c7dec8 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -454,6 +454,7 @@ static inline int neigh_hh_bridge(struct hh_cache *hh, struct sk_buff *skb)
static inline int neigh_hh_output(const struct hh_cache *hh, struct sk_buff *skb)
{
+ unsigned int hh_alen = 0;
unsigned int seq;
unsigned int hh_len;
@@ -461,16 +462,33 @@ static inline int neigh_hh_output(const struct hh_cache *hh, struct sk_buff *skb
seq = read_seqbegin(&hh->hh_lock);
hh_len = hh->hh_len;
if (likely(hh_len <= HH_DATA_MOD)) {
- /* this is inlined by gcc */
- memcpy(skb->data - HH_DATA_MOD, hh->hh_data, HH_DATA_MOD);
+ hh_alen = HH_DATA_MOD;
+
+ /* skb_push() would proceed silently if we have room for
+ * the unaligned size but not for the aligned size:
+ * check headroom explicitly.
+ */
+ if (likely(skb_headroom(skb) >= HH_DATA_MOD)) {
+ /* this is inlined by gcc */
+ memcpy(skb->data - HH_DATA_MOD, hh->hh_data,
+ HH_DATA_MOD);
+ }
} else {
- unsigned int hh_alen = HH_DATA_ALIGN(hh_len);
+ hh_alen = HH_DATA_ALIGN(hh_len);
- memcpy(skb->data - hh_alen, hh->hh_data, hh_alen);
+ if (likely(skb_headroom(skb) >= hh_alen)) {
+ memcpy(skb->data - hh_alen, hh->hh_data,
+ hh_alen);
+ }
}
} while (read_seqretry(&hh->hh_lock, seq));
- skb_push(skb, hh_len);
+ if (WARN_ON_ONCE(skb_headroom(skb) < hh_alen)) {
+ kfree_skb(skb);
+ return NET_XMIT_DROP;
+ }
+
+ __skb_push(skb, hh_len);
return dev_queue_xmit(skb);
}