ipv6: ioam: fix heap buffer overflow in __ioam6_fill_trace_data()

[ Upstream commit 6db8b56eed62baacaf37486e83378a72635c04cc ]

On the receive path, __ioam6_fill_trace_data() uses trace->nodelen
to decide how much data to write for each node. It trusts this field
as-is from the incoming packet, with no consistency check against
trace->type (the 24-bit field that tells which data items are
present). A crafted packet can set nodelen=0 while setting type bits
0-21, causing the function to write ~100 bytes past the allocated
region (into skb_shared_info), which corrupts adjacent heap memory
and leads to a kernel panic.

Add a shared helper ioam6_trace_compute_nodelen() in ioam6.c to
derive the expected nodelen from the type field, and use it:

  - in ioam6_iptunnel.c (send path, existing validation) to replace
    the open-coded computation;
  - in exthdrs.c (receive path, ipv6_hop_ioam) to drop packets whose
    nodelen is inconsistent with the type field, before any data is
    written.

Per RFC 9197, bits 12-21 are each short (4-octet) fields, so they
are included in IOAM6_MASK_SHORT_FIELDS (changed from 0xff100000 to
0xff1ffc00).

Fixes: 9ee11f0fff20 ("ipv6: ioam: Data plane support for Pre-allocated Trace")
Cc: stable@vger.kernel.org
Signed-off-by: Junxi Qian <qjx1298677004@gmail.com>
Reviewed-by: Justin Iurman <justin.iurman@gmail.com>
Link: https://patch.msgid.link/20260211040412.86195-1-qjx1298677004@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/net/ioam6.h b/include/net/ioam6.h
index 781d2d8b2f29..3f99eb445de6 100644
--- a/include/net/ioam6.h
+++ b/include/net/ioam6.h
@@ -59,6 +59,8 @@ void ioam6_fill_trace_data(struct sk_buff *skb,
 			   struct ioam6_trace_hdr *trace,
 			   bool is_input);
 
+u8 ioam6_trace_compute_nodelen(u32 trace_type);
+
 int ioam6_init(void);
 void ioam6_exit(void);