From: Peter Oskolkov posk@google.com
commit 0ff89efb524631ac9901b81446b453c29711c376 upstream
The current behavior of IP defragmentation is inconsistent: - some overlapping/wrong length fragments are dropped without affecting the queue; - most overlapping fragments cause the whole frag queue to be dropped.
This patch brings consistency: if a bad fragment is detected, the whole frag queue is dropped. Two major benefits: - fail fast: corrupted frag queues are cleared immediately, instead of by timeout; - testing of overlapping fragments is now much easier: any kind of random fragment length mutation now leads to the frag queue being discarded (IP packet dropped); before this patch, some overlaps were "corrected", with tests not seeing expected packet drops.
Note that in one case (see "if (end&7)" conditional) the current behavior is preserved as there are concerns that this could be legitimate padding.
Signed-off-by: Peter Oskolkov posk@google.com Reviewed-by: Eric Dumazet edumazet@google.com Reviewed-by: Willem de Bruijn willemb@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Zubin Mithra zsm@chromium.org --- Backport Note: - Syzkaller reported a UAF, as 0ff89efb5246 ("ip: fail fast on IP defrag errors") was not applied prior to applying d5f9565c8d5a ("net: ipv4: do not handle duplicate fragments as overlapping"). Conflicts occur when 0ff89efb5246 is now applied onto 4.14.y/4.19.y, which this patch addresses. - An alternative to this patch would be to do the following :- - revert "net: ipv4: do not handle duplicate fragments as overlapping" (d5f9565c8d5ad on 4.19.y, 95b4b711444a on 4.14.y) - apply "ip: fail fast on IP defrag errors" (0ff89efb5246) - apply "net: ipv4: do not handle duplicate fragments as overlapping" (ade446403bfb)
net/ipv4/ip_fragment.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-)
diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c index f8bbd693c19c2..03576ff7557e0 100644 --- a/net/ipv4/ip_fragment.c +++ b/net/ipv4/ip_fragment.c @@ -382,7 +382,7 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb) */ if (end < qp->q.len || ((qp->q.flags & INET_FRAG_LAST_IN) && end != qp->q.len)) - goto err; + goto discard_qp; qp->q.flags |= INET_FRAG_LAST_IN; qp->q.len = end; } else { @@ -394,20 +394,20 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb) if (end > qp->q.len) { /* Some bits beyond end -> corruption. */ if (qp->q.flags & INET_FRAG_LAST_IN) - goto err; + goto discard_qp; qp->q.len = end; } } if (end == offset) - goto err; + goto discard_qp;
err = -ENOMEM; if (!pskb_pull(skb, skb_network_offset(skb) + ihl)) - goto err; + goto discard_qp;
err = pskb_trim_rcsum(skb, end - offset); if (err) - goto err; + goto discard_qp;
/* Note : skb->rbnode and skb->dev share the same location. */ dev = skb->dev; @@ -425,6 +425,7 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb) * fragment. */
+ err = -EINVAL; /* Find out where to put this fragment. */ prev_tail = qp->q.fragments_tail; if (!prev_tail) @@ -433,7 +434,7 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb) /* This is the common case: skb goes to the end. */ /* Detect and discard overlaps. */ if (offset < prev_tail->ip_defrag_offset + prev_tail->len) - goto discard_qp; + goto overlap; if (offset == prev_tail->ip_defrag_offset + prev_tail->len) ip4_frag_append_to_last_run(&qp->q, skb); else @@ -456,7 +457,7 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb) end <= skb1_run_end) goto err; /* No new data, potential duplicate */ else - goto discard_qp; /* Found an overlap */ + goto overlap; /* Found an overlap */ } while (*rbn); /* Here we have parent properly set, and rbn pointing to * one of its NULL left/right children. Insert skb. @@ -493,16 +494,18 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb) skb->_skb_refdst = 0UL; err = ip_frag_reasm(qp, skb, prev_tail, dev); skb->_skb_refdst = orefdst; + if (err) + inet_frag_kill(&qp->q); return err; }
skb_dst_drop(skb); return -EINPROGRESS;
+overlap: + __IP_INC_STATS(net, IPSTATS_MIB_REASM_OVERLAPS); discard_qp: inet_frag_kill(&qp->q); - err = -EINVAL; - __IP_INC_STATS(net, IPSTATS_MIB_REASM_OVERLAPS); err: kfree_skb(skb); return err;