linux-stable.git/net/ipv6, branch v7.2.4

seg6: reset IP6CB after IPv6 decapsulation

2026-09-07T15:37:21+00:00

commit f967455fb2a5a2079b9eb5823e9ccf359174bf9f upstream.

decap_and_validate() pulls the outer SRv6 headers and makes the inner
packet the skb network header. The IPv6 control block still contains
values collected while parsing the outer packet, including nhoff and
extension-header flags.

End.DX6 and End.DT6 route the inner IPv6 packet directly to the IPv6
input path. An unprivileged user can reach End.DT6 from a user and net
namespace by installing a local SID and injecting an outer packet with
Hop-by-Hop and Destination Options headers followed by an SRH and a
minimal inner IPv6 packet.

The outer extension headers leave a large nhoff in IP6CB. After
decapsulation, ip6_protocol_deliver_rcu() uses that stale offset on the
inner packet and reads beyond the skb head. KASAN reports:

  BUG: KASAN: slab-out-of-bounds in ip6_protocol_deliver_rcu
  ip6_protocol_deliver_rcu+0x1118/0x1450
  ip6_input_finish+0x11b/0x240
  seg6_local_input_core+0xed/0x2e0
  lwtunnel_input+0x1e9/0x4e0
  ipv6_rthdr_rcv+0x525f/0x6c50
  ip6_protocol_deliver_rcu+0xcb7/0x1450

Before clearing IP6CB for an inner IPv6 packet, save its incoming
interface index and L3 slave state. Restore both after the clear and set
nhoff to the inner IPv6 base-header nexthdr field.

Use IP6CB(skb)->iif rather than skb->skb_iif because VRF processing can
replace skb_iif with the L3 master while IP6CB keeps the receiving
interface. Preserve IP6SKB_L3SLAVE for the same reason.

Fixes: d7a669dd2f8b ("ipv6: sr: add helper functions for seg6local")
Cc: stable@vger.kernel.org
Reported-by: Vega 
Signed-off-by: Zhiling Zou 
Reviewed-by: Andrea Mayer 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman

net: cap advertised IP tunnel headroom

2026-09-07T15:37:21+00:00

commit 6b222adeb9340306e2ff97127c76117abb9b3df8 upstream.

IP tunnel devices derive their advertised needed_headroom from lower
output devices. A stack of user-created devices can make the derived
value larger than the 16-bit skb header offsets can represent. Once IP
output reserves it, skb head expansion can wrap those offsets.

The runtime transmit path already caps a growing needed_headroom at 512.
Apply the same cap when tunnel configuration publishes needed_headroom
derived from a lower output device.

Capping the advertised value is safe: IP tunnel transmit still expands
the skb when a packet needs more headroom. A nonsensical stacked
configuration can therefore incur an extra reallocation, but it cannot
publish an unbounded reservation to upper layers.

Fixes: 1a37e412a022 ("net: Use 16bits for *_headers fields of struct skbuff")
Cc: stable@vger.kernel.org
Reported-by: Vega 
Signed-off-by: Zhiling Zou 
Reviewed-by: Ido Schimmel 
Link: https://patch.msgid.link/ba04a1fd6bfae2377607fad5d8f80f7eb80fd4c4.1786542637.git.zhilinz@nebusec.ai
Signed-off-by: Paolo Abeni 
Signed-off-by: Greg Kroah-Hartman

ipv6: use RCU iterator to dump route exceptions

2026-09-07T15:36:59+00:00

commit 47cdab0d51aaa9bd85f8e4904585bd5bd4df4488 upstream.

rt6_nh_dump_exceptions() uses hlist_for_each_entry() to iterate over
RCU-protected exception lists. The caller holds rcu_read_lock(), but does
not hold rt6_exception_lock, so rt6_insert_exception() can concurrently
add an entry with hlist_add_head_rcu().

KCSAN reports this race (irrelevant details omitted):

  ==================================================================
  BUG: KCSAN: data-race in rt6_insert_exception / rt6_nh_dump_exceptions

  write (marked) to 0xffff8a7c44c59620 of 8 bytes by interrupt on cpu 5:
    rt6_insert_exception+0x3bb/0x760
    __ip6_rt_update_pmtu+0x4fe/0x750
    ip6_sk_update_pmtu+0x19a/0x3b0
    udpv6_err+0x3ff/0x800
    icmpv6_notify+0x1e1/0x440
    icmpv6_rcv+0x8c0/0xab0
    ip6_protocol_deliver_rcu+0x616/0x840
    ip6_input_finish+0xb9/0x160
    ...
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

  read to 0xffff8a7c44c59620 of 8 bytes by task 549 on cpu 14:
    rt6_nh_dump_exceptions+0xb3/0x260
    rt6_dump_route+0x53e/0x5f0
    fib6_dump_node+0x6d/0xf0
    fib6_walk_continue+0x290/0x2d0
    fib6_dump_table+0x28d/0x360
    inet6_dump_fib+0x37d/0x620
    rtnl_dumpit+0x7b/0xd0
    netlink_dump+0x3ae/0x7e0
    ...
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

  4 locks held by dumper/549:
    ...
    #1: (rcu_read_lock){....}-{1:3}, at: inet6_dump_fib+0x88/0x620
    #2: (&tb->tb6_lock){+.-.}-{3:3}, at: fib6_dump_table+0x1e9/0x360
    #3: (rcu_read_lock){....}-{1:3}, at: rt6_dump_route+0x483/0x5f0

  value changed: 0xffff8a7c44e05700 -> 0xffff8a7c45d60100

  Reported by Kernel Concurrency Sanitizer on:
  CPU: 14 UID: 0 PID: 549 Comm: dumper Not tainted
  7.2.0-rc7-virtme #38 PREEMPT(lazy)
  ...

Use hlist_for_each_entry_rcu() to safely iterate over the exception list.

Fixes: 1e47b4837f3b ("ipv6: Dump route exceptions if requested")
Cc: stable@vger.kernel.org
Signed-off-by: Yuyang Huang 
Reviewed-by: Stefano Brivio 
Reviewed-by: Ido Schimmel 
Link: https://patch.msgid.link/20260815084651.69477-1-sigefriedhyy@gmail.com
Signed-off-by: David S. Miller 
Signed-off-by: Jakub Kicinski 
Signed-off-by: Greg Kroah-Hartman

ipv6: rpl: fix NULL dereference of idev in ipv6_rpl_srh_rcv()

2026-09-07T15:36:59+00:00

commit f826df95332c07380206dbd54178b6eefb311aba upstream.

ipv6_rpl_srh_rcv() dereferences idev from __in6_dev_get() without a NULL
check when reading idev->cnf.rpl_seg_enabled.

When the device's MTU drops below IPV6_MIN_MTU, addrconf_ifdown() clears
dev->ip6_ptr through RCU_INIT_POINTER(). A packet that passed the idev
check in ip6_rcv_core() can then reach ipv6_rpl_srh_rcv() with
dev->ip6_ptr already NULL.

Reproduced by flooding the receiving interface with ping6 traffic while
flapping its MTU between 1500 and 1200:

 BUG: KASAN: null-ptr-deref in ipv6_rpl_srh_rcv+0xb3/0x1070
 Read of size 4 at addr 00000000000006b4 by task ping6/394

 CPU: 2 UID: 0 PID: 394 Comm: ping6 Not tainted 7.2.0-rc7-micro-vm-dev-00095-g24ef02f934ee #240 PREEMPT(full)
 Call Trace:
  
  kasan_report+0xc6/0x100
  ipv6_rpl_srh_rcv+0xb3/0x1070
  ip6_protocol_deliver_rcu+0x759/0x9a0
  ip6_input_finish+0xa8/0x1b0
  ip6_input+0xe1/0x490
  ipv6_rcv+0x33d/0x460
  __netif_receive_skb_one_core+0xd6/0x130
  process_backlog+0x2cc/0xa00
  __napi_poll.constprop.0+0x56/0x270
  net_rx_action+0x327/0x730
  handle_softirqs+0x11e/0x630
  do_softirq+0xb3/0xf0
  

Both ipv6_rpl_srh_rcv() and ipv6_srh_rcv() are called only from
ipv6_rthdr_rcv(), which already has an idev lookup.

Fix the NULL dereference on the RPL path by checking idev in
ipv6_rthdr_rcv(), before it calls either function. The callees take idev as
an argument and no longer call __in6_dev_get(), so the packet is now
dropped in one place, with SKB_DROP_REASON_IPV6DISABLED on both paths.

Fixes: 8610c7c6e3bd ("net: ipv6: add support for rpl sr exthdr")
Cc: stable@vger.kernel.org
Signed-off-by: Andrea Mayer 
Tested-by: Xiang Mei 
Reviewed-by: Simon Horman 
Link: https://patch.msgid.link/20260817132644.2223-1-andrea.mayer@uniroma2.it
Signed-off-by: Jakub Kicinski 
Signed-off-by: Greg Kroah-Hartman

ip6_gre: fix hardware header length for NBMA tunnels

2026-09-07T15:36:58+00:00

commit 505b6d296c486ef7d1274f279d4c43a172f63224 upstream.

ip6gre_tnl_link_config_route() accumulates the lower device's hardware
header length into dev->hard_header_len whenever header_ops is set. This
is incorrect for both users of header_ops.

ip6gretap and ip6erspan have a fixed Ethernet hardware header length.
For an NBMA ip6gre tunnel, ip6gre_header() creates only the GRE header,
the optional FOU or GUE header, and the outer IPv6 header. The lower
device header is headroom needed later, not part of the tunnel device's
hardware header.

Keep the lower device header in needed_headroom. Set hard_header_len to
the tunnel header length only for ARPHRD_IP6GRE devices with header_ops,
and leave the fixed Ethernet header length unchanged for tap and erspan
devices.

Fixes: 832ba596494b ("net: ip6_gre: set dev->hard_header_len when using header_ops")
Cc: stable@vger.kernel.org
Suggested-by: Ido Schimmel 
Signed-off-by: Zhiling Zou 
Reviewed-by: Ido Schimmel 
Link: https://patch.msgid.link/64b46542bbe1701f07702aaa50273e2a87903db5.1786542637.git.zhilinz@nebusec.ai
Signed-off-by: Paolo Abeni 
Signed-off-by: Greg Kroah-Hartman

ip6_tunnel: use skb_cow_head() in ip6_tnl_xmit()

2026-09-07T15:36:58+00:00

commit 87f21b59ddc618eff9670c174842964ad65fdade upstream.

ip6_tnl_xmit() may need to expand headroom before it can push the
outer IPv6 and optional encap headers. It currently does that with
skb_realloc_headroom(), copies skb->sk ownership, consumes the original
skb, and then continues processing with the replacement skb kept only in
its local variable.

That is safe only if the helper cannot fail afterwards. But this helper
still has post-reallocation error exits. collect_md tunnels reject
non-NONE encap after the replacement, and ip6_tnl_encap() can also fail
later. In those cases the helper returns an error to its callers while
the caller still only has the original skb pointer.

Both ip6_tnl_start_xmit() and the IPv6 GRE paths free the caller skb on
error, so they can end up freeing an skb that ip6_tnl_xmit() already
consumed.

Use skb_cow_head() instead. It provides the required headroom and
writability without privately replacing the caller-owned skb, so later
error returns cannot leave callers with a stale pointer.

The Ethernet users, ip6gretap and ip6erspan, clear IFF_TX_SKB_SHARING
and already call skb_cow_head() before entering ip6_tnl_xmit(). They do
not rely on the removed skb_shared() reallocation. This also makes the
IPv6 tunnel path consistent with ip_tunnel_xmit().

Fixes: 058214a4d1df ("ip6_tun: Add infrastructure for doing encapsulation")
Cc: stable@vger.kernel.org
Reported-by: Vega 
Reviewed-by: Ido Schimmel 
Signed-off-by: Zhiling Zou 
Link: https://patch.msgid.link/30807a062ccc5c9c8a5ec2c5eb805ef279c50bdd.1786452593.git.zhilinz@nebusec.ai
Signed-off-by: Jakub Kicinski 
Signed-off-by: Greg Kroah-Hartman

ip: orphan prefetched skbs before multicast forwarding

2026-09-07T15:36:58+00:00

commit e36ce6e78fe3fc3c071a26750783b7ba081ce10d upstream.

IPv4 and IPv6 input preserve an skb->sk association installed by
bpf_sk_assign() so that local delivery can use the selected socket under
RCU. Both address families can also prefetch a socket in UDP early demux.
In both paths (BPF and UDP early demux) a reference is not guaranteed to
be held on the socket.

When a multicast packet is not locally deliverable, IPv6 hands the
original skb to ip6_mr_input(). IPv4's ip_mr_input() similarly keeps the
original skb when local delivery is not needed. Either path can put the
skb on an unresolved multicast route queue or forward it after the
receive-side RCU section ends.

After the prefetched socket is destroyed, a later skb free invokes
sock_pfree() and dereferences the stale skb->sk. Orphan the skb before
each non-local multicast forwarding path. Local delivery retains the
original skb; the existing skb_clone() calls provide multicast forwarding
with a socket-free clone.

Fixes: cf7fbe660f2d ("bpf: Add socket assign support")
Fixes: 08842c43d016 ("udp: no longer touch sk->sk_refcnt in early demux")
Cc: stable@vger.kernel.org
Reported-by: Vega 
Signed-off-by: Zhiling Zou 
Reported-by: Vega 
Signed-off-by: Zhiling Zou 
Reviewed-by: Ido Schimmel 
Link: https://patch.msgid.link/0c52eb3d7532aaf8bccf37e0f7c922143c639735.1786552223.git.zhilinz@nebusec.ai
Signed-off-by: Paolo Abeni 
Signed-off-by: Greg Kroah-Hartman

ipv6: seg6: clear IPv4 control block on IPIP decapsulation

2026-09-02T12:33:19+00:00

commit 44930446dde45a7a90fe1446fa38eb0e2c561646 upstream.

End.DX4 and End.DT4 decapsulate an IPv4 packet through
decap_and_validate() and send it directly to IPv4 routing. The inner
packet therefore bypasses ip_rcv_core(), which normally clears IPCB
before IPv4 interprets skb->cb.

The skb instead retains IP6CB data from the outer packet. IP6CB and
IPCB use the same skb->cb storage, so IP6CB(skb)->lastopt overlaps
IPCB(skb)->opt.optlen and srr, while IP6CB(skb)->nhoff overlaps rr and
ts.

The sender can make the stale optlen byte nonzero with a valid outer
extension-header chain. The reproducers put an eight-byte Destination
Options header immediately after the 40-byte IPv6 header and before the
Segment Routing Header. ipv6_destopt_rcv() records the sender-controlled
Destination Options offset in both lastopt and nhoff, setting them to
40. On the reproduced little-endian x86-64 kernel, IPv4 therefore sees
optlen = 40 and rr = 40.

Both tcp_v4_save_options() and __ip_options_echo() skip option copying
when optlen is zero. Here optlen is 40, so the TCP SYN path allocates
room for 40 bytes of option data and calls __ip_options_echo(). The
stale rr value makes that function read inner packet byte 41 as the
Record Route option length. The reproducers set that sender-controlled
byte to 255, so __ip_options_echo() copies 255 bytes into the 40-byte
option-data area.

Separate End.DX4 and End.DT4 reproducers on the unpatched v7.2-rc5
kernel both produced:

  BUG: KASAN: slab-out-of-bounds in __ip_options_echo()
  Write of size 255

The relevant End.DX4 call path is:

  __ip_options_echo
  tcp_v4_route_req
  tcp_conn_request
  tcp_v4_conn_request
  tcp_rcv_state_process
  tcp_v4_do_rcv
  tcp_v4_rcv
  ip_protocol_deliver_rcu
  ip_local_deliver_finish
  ip_local_deliver
  input_action_end_dx4_finish
  input_action_end_dx4

The relevant End.DT4 call path is:

  __ip_options_echo
  tcp_v4_route_req
  tcp_conn_request
  tcp_v4_conn_request
  tcp_rcv_state_process
  tcp_v4_do_rcv
  tcp_v4_rcv
  ip_protocol_deliver_rcu
  ip_local_deliver_finish
  ip_local_deliver
  input_action_end_dt4

tcp_v4_save_options() is inlined into the tcp_v4_route_req() path, so
it does not appear as a separate frame.

When decap_and_validate() handles IPPROTO_IPIP, save the ingress
interface from IP6CB, clear IPCB, and restore the saved value. Doing
this in the common decapsulation path covers End.DX4, End.DT4, and
End.DT46's IPv4 arm.

Use IP6CB(skb)->iif rather than skb->skb_iif. These actions run after
l3mdev processing, which can replace skb_iif with the L3 master;
IP6CB iif still records the receiving interface set at IPv6 ingress.

Fixes: 891ef8dd2a8d ("ipv6: sr: implement additional seg6local actions")
Cc: stable@vger.kernel.org
Suggested-by: Andrea Mayer 
Signed-off-by: Kyle Zeng 
Co-developed-by: David Lee 
Signed-off-by: David Lee 
Reviewed-by: Andrea Mayer 
Link: https://patch.msgid.link/20260817085839.946321-1-david.lee@trailofbits.com
Signed-off-by: Jakub Kicinski 
Signed-off-by: Greg Kroah-Hartman

xfrm: ah6: validate routing header segments_left

2026-09-02T12:33:19+00:00

commit 7bad4bda74dc4713f398d3b7624ff05478e3a568 upstream.

AH6 rearranges routing-header addresses before computing or verifying the
ICV. ipv6_rearrange_rthdr() assumes that segments_left is not larger than
the number of addresses described by the routing header's hdrlen field.

That assumption does not hold for raw IPv6 HDRINCL packets. A packet with
hdrlen equal to 2 describes one address, but can carry an arbitrary
segments_left value. With segments_left equal to 255, the function moves
its address pointer 4,064 bytes backwards and passes a 4,064-byte length to
memmove(), resulting in an out-of-bounds access.

Validate the invariant locally before modifying the routing header or
performing any address-pointer arithmetic, and propagate malformed-header
errors to the existing AH6 input and output error paths.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Assisted-by: avom-custom-harness:gpt-5.5-qwen3.6-mod-mix
Signed-off-by: Asim Viladi Oglu Manizada 
Signed-off-by: Steffen Klassert 
Signed-off-by: Greg Kroah-Hartman

tcp: clamp route advmss to TCP_MIN_MSS

2026-09-02T12:33:19+00:00

commit 870a9e42ecc6fe1b8c25d87af043cb0d9c178fe1 upstream.

tcp_select_initial_window() assumes that callers never pass an MSS
smaller than 1, but route-derived advmss values can violate that
assumption.

A too-small explicit RTAX_ADVMSS is one way to get there, but it is not
the only one. The same divide-by-zero can also be reached through the
"default advmss" path when RTAX_ADVMSS is left at 0 and the effective
advmss is later driven down by route MTU and min_adv_mss.

Introduce a tcp_dst_advmss() helper that clamps route advmss to
TCP_MIN_MSS before TCP consumes it, and use it in the TCP paths that
derive advmss from dst metrics. This keeps the effective MSS from
dropping to zero before tcp_select_initial_window() rounds the receive
window.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Reported-by: Vega 
Signed-off-by: Yong Wang 
Signed-off-by: Ren Wei 
Link: https://patch.msgid.link/251eaf8277fa7c66364c9815c5da01662d269181.1787074852.git.edragain@163.com
Signed-off-by: Jakub Kicinski 
Signed-off-by: Greg Kroah-Hartman