[PATCH net] ipv6: ioam: fix potential NULL dereferences in __ioam6_fill_trace_data()

Eric Dumazet
2026-04-02T10:17:34Z

We need to check __in6_dev_get() for possible NULL value, as
suggested by Yiming Qian.

Also add skb_dst_dev_rcu() instead of skb_dst_dev(),
and two missing READ_ONCE().

Note that @dev can't be NULL.

Fixes: 9ee11f0fff20 ("ipv6: ioam: Data plane support for Pre-allocated Trace")
Reported-by: Yiming Qian <yimingqian591@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Justin Iurman <justin.iurman@gmail.com>
---
net/ipv6/ioam6.c | 27 ++++++++++++++++-----------
1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/net/ipv6/ioam6.c b/net/ipv6/ioam6.c
index 3978773bec424890cd18db78cf7cac9d3d652130..05a0b7d7e2aac35f634641fc4a791d1965dc85fd 100644
--- a/net/ipv6/ioam6.c
+++ b/net/ipv6/ioam6.c
@@ -710,7 +710,9 @@ static void __ioam6_fill_trace_data(struct sk_buff *skb,
struct ioam6_schema *sc,
unsigned int sclen, bool is_input)
{
- struct net_device *dev = skb_dst_dev(skb);
+ /* Note: skb_dst_dev_rcu() can't be NULL at this point. */
+ struct net_device *dev = skb_dst_dev_rcu(skb);
+ struct inet6_dev *i_skb_dev, *idev;
struct timespec64 ts;
ktime_t tstamp;
u64 raw64;
@@ -721,13 +723,16 @@ static void __ioam6_fill_trace_data(struct sk_buff *skb,

data = trace->data + trace->remlen * 4 - trace->nodelen * 4 - sclen * 4;

+ i_skb_dev = skb->dev ? __in6_dev_get(skb->dev) : NULL;
+ idev = __in6_dev_get(dev);
+
/* hop_lim and node_id */
if (trace->type.bit0) {
byte = ipv6_hdr(skb)->hop_limit;
if (is_input)
byte--;

- raw32 = dev_net(dev)->ipv6.sysctl.ioam6_id;
+ raw32 = READ_ONCE(dev_net(dev)->ipv6.sysctl.ioam6_id);

*(__be32 *)data = cpu_to_be32((byte << 24) | raw32);
data += sizeof(__be32);
@@ -735,18 +740,18 @@ static void __ioam6_fill_trace_data(struct sk_buff *skb,

/* ingress_if_id and egress_if_id */
if (trace->type.bit1) {
- if (!skb->dev)
+ if (!i_skb_dev)
raw16 = IOAM6_U16_UNAVAILABLE;
else
- raw16 = (__force u16)READ_ONCE(__in6_dev_get(skb->dev)->cnf.ioam6_id);
+ raw16 = (__force u16)READ_ONCE(i_skb_dev->cnf.ioam6_id);

*(__be16 *)data = cpu_to_be16(raw16);
data += sizeof(__be16);

- if (dev->flags & IFF_LOOPBACK)
+ if ((dev->flags & IFF_LOOPBACK) || !idev)
raw16 = IOAM6_U16_UNAVAILABLE;
else
- raw16 = (__force u16)READ_ONCE(__in6_dev_get(dev)->cnf.ioam6_id);
+ raw16 = (__force u16)READ_ONCE(idev->cnf.ioam6_id);

*(__be16 *)data = cpu_to_be16(raw16);
data += sizeof(__be16);
@@ -822,7 +827,7 @@ static void __ioam6_fill_trace_data(struct sk_buff *skb,
if (is_input)
byte--;

- raw64 = dev_net(dev)->ipv6.sysctl.ioam6_id_wide;
+ raw64 = READ_ONCE(dev_net(dev)->ipv6.sysctl.ioam6_id_wide);

*(__be64 *)data = cpu_to_be64(((u64)byte << 56) | raw64);
data += sizeof(__be64);
@@ -830,18 +835,18 @@ static void __ioam6_fill_trace_data(struct sk_buff *skb,

/* ingress_if_id and egress_if_id (wide) */
if (trace->type.bit9) {
- if (!skb->dev)
+ if (!i_skb_dev)
raw32 = IOAM6_U32_UNAVAILABLE;
else
- raw32 = READ_ONCE(__in6_dev_get(skb->dev)->cnf.ioam6_id_wide);
+ raw32 = READ_ONCE(i_skb_dev->cnf.ioam6_id_wide);

*(__be32 *)data = cpu_to_be32(raw32);
data += sizeof(__be32);

- if (dev->flags & IFF_LOOPBACK)
+ if ((dev->flags & IFF_LOOPBACK) || !idev)
raw32 = IOAM6_U32_UNAVAILABLE;
else
- raw32 = READ_ONCE(__in6_dev_get(dev)->cnf.ioam6_id_wide);
+ raw32 = READ_ONCE(idev->cnf.ioam6_id_wide);

*(__be32 *)data = cpu_to_be32(raw32);
data += sizeof(__be32);
--
2.53.0.1185.g05d4b7b318-goog