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Subject[PATCH 4.14 22/62] net: create skb_gso_validate_mac_len()
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

commit 2b16f048729bf35e6c28a40cbfad07239f9dcd90 upstream

If you take a GSO skb, and split it into packets, will the MAC
length (L2 + L3 + L4 headers + payload) of those packets be small
enough to fit within a given length?

Move skb_gso_mac_seglen() to skbuff.h with other related functions
like skb_gso_network_seglen() so we can use it, and then create
skb_gso_validate_mac_len to do the full calculation.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
[jwang: cherry pick for CVE-2018-1000026]
Signed-off-by: Jack Wang <jinpu.wang@cloud.ionos.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/skbuff.h | 16 +++++++++++
net/core/skbuff.c | 63 +++++++++++++++++++++++++++++++++---------
net/sched/sch_tbf.c | 10 -------
3 files changed, 66 insertions(+), 23 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 39c2570ddcf6..50a4a5968f3a 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -3317,6 +3317,7 @@ int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen);
void skb_scrub_packet(struct sk_buff *skb, bool xnet);
unsigned int skb_gso_transport_seglen(const struct sk_buff *skb);
bool skb_gso_validate_mtu(const struct sk_buff *skb, unsigned int mtu);
+bool skb_gso_validate_mac_len(const struct sk_buff *skb, unsigned int len);
struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features);
struct sk_buff *skb_vlan_untag(struct sk_buff *skb);
int skb_ensure_writable(struct sk_buff *skb, int write_len);
@@ -4087,6 +4088,21 @@ static inline unsigned int skb_gso_network_seglen(const struct sk_buff *skb)
return hdr_len + skb_gso_transport_seglen(skb);
}

+/**
+ * skb_gso_mac_seglen - Return length of individual segments of a gso packet
+ *
+ * @skb: GSO skb
+ *
+ * skb_gso_mac_seglen is used to determine the real size of the
+ * individual segments, including MAC/L2, Layer3 (IP, IPv6) and L4
+ * headers (TCP/UDP).
+ */
+static inline unsigned int skb_gso_mac_seglen(const struct sk_buff *skb)
+{
+ unsigned int hdr_len = skb_transport_header(skb) - skb_mac_header(skb);
+ return hdr_len + skb_gso_transport_seglen(skb);
+}
+
/* Local Checksum Offload.
* Compute outer checksum based on the assumption that the
* inner checksum will be offloaded later.
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 873032d1a083..6dbd2c54b2c9 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4930,37 +4930,74 @@ unsigned int skb_gso_transport_seglen(const struct sk_buff *skb)
EXPORT_SYMBOL_GPL(skb_gso_transport_seglen);

/**
- * skb_gso_validate_mtu - Return in case such skb fits a given MTU
+ * skb_gso_size_check - check the skb size, considering GSO_BY_FRAGS
*
- * @skb: GSO skb
- * @mtu: MTU to validate against
+ * There are a couple of instances where we have a GSO skb, and we
+ * want to determine what size it would be after it is segmented.
*
- * skb_gso_validate_mtu validates if a given skb will fit a wanted MTU
- * once split.
+ * We might want to check:
+ * - L3+L4+payload size (e.g. IP forwarding)
+ * - L2+L3+L4+payload size (e.g. sanity check before passing to driver)
+ *
+ * This is a helper to do that correctly considering GSO_BY_FRAGS.
+ *
+ * @seg_len: The segmented length (from skb_gso_*_seglen). In the
+ * GSO_BY_FRAGS case this will be [header sizes + GSO_BY_FRAGS].
+ *
+ * @max_len: The maximum permissible length.
+ *
+ * Returns true if the segmented length <= max length.
*/
-bool skb_gso_validate_mtu(const struct sk_buff *skb, unsigned int mtu)
-{
+static inline bool skb_gso_size_check(const struct sk_buff *skb,
+ unsigned int seg_len,
+ unsigned int max_len) {
const struct skb_shared_info *shinfo = skb_shinfo(skb);
const struct sk_buff *iter;
- unsigned int hlen;
-
- hlen = skb_gso_network_seglen(skb);

if (shinfo->gso_size != GSO_BY_FRAGS)
- return hlen <= mtu;
+ return seg_len <= max_len;

/* Undo this so we can re-use header sizes */
- hlen -= GSO_BY_FRAGS;
+ seg_len -= GSO_BY_FRAGS;

skb_walk_frags(skb, iter) {
- if (hlen + skb_headlen(iter) > mtu)
+ if (seg_len + skb_headlen(iter) > max_len)
return false;
}

return true;
}
+
+/**
+ * skb_gso_validate_mtu - Return in case such skb fits a given MTU
+ *
+ * @skb: GSO skb
+ * @mtu: MTU to validate against
+ *
+ * skb_gso_validate_mtu validates if a given skb will fit a wanted MTU
+ * once split.
+ */
+bool skb_gso_validate_mtu(const struct sk_buff *skb, unsigned int mtu)
+{
+ return skb_gso_size_check(skb, skb_gso_network_seglen(skb), mtu);
+}
EXPORT_SYMBOL_GPL(skb_gso_validate_mtu);

+/**
+ * skb_gso_validate_mac_len - Will a split GSO skb fit in a given length?
+ *
+ * @skb: GSO skb
+ * @len: length to validate against
+ *
+ * skb_gso_validate_mac_len validates if a given skb will fit a wanted
+ * length once split, including L2, L3 and L4 headers and the payload.
+ */
+bool skb_gso_validate_mac_len(const struct sk_buff *skb, unsigned int len)
+{
+ return skb_gso_size_check(skb, skb_gso_mac_seglen(skb), len);
+}
+EXPORT_SYMBOL_GPL(skb_gso_validate_mac_len);
+
static struct sk_buff *skb_reorder_vlan_header(struct sk_buff *skb)
{
int mac_len;
diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c
index b36ecb58aa6e..107cc76b6e24 100644
--- a/net/sched/sch_tbf.c
+++ b/net/sched/sch_tbf.c
@@ -142,16 +142,6 @@ static u64 psched_ns_t2l(const struct psched_ratecfg *r,
return len;
}

-/*
- * Return length of individual segments of a gso packet,
- * including all headers (MAC, IP, TCP/UDP)
- */
-static unsigned int skb_gso_mac_seglen(const struct sk_buff *skb)
-{
- unsigned int hdr_len = skb_transport_header(skb) - skb_mac_header(skb);
- return hdr_len + skb_gso_transport_seglen(skb);
-}
-
/* GSO packet is too big, segment it so that tbf can transmit
* each segment in time
*/
--
2.19.1


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