linux-cve-announce - CVE-2025-38476: rpl: Fix use-after-free in rpl_do_srh

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Message-ID: <2025072813-CVE-2025-38476-ab35@gregkh>
Date: Mon, 28 Jul 2025 13:22:19 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38476: rpl: Fix use-after-free in rpl_do_srh_inline().

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

rpl: Fix use-after-free in rpl_do_srh_inline().

Running lwt_dst_cache_ref_loop.sh in selftest with KASAN triggers
the splat below [0].

rpl_do_srh_inline() fetches ipv6_hdr(skb) and accesses it after
skb_cow_head(), which is illegal as the header could be freed then.

Let's fix it by making oldhdr to a local struct instead of a pointer.

[0]:
[root@...ora net]# ./lwt_dst_cache_ref_loop.sh
...
TEST: rpl (input)
[   57.631529] ==================================================================
BUG: KASAN: slab-use-after-free in rpl_do_srh_inline.isra.0 (net/ipv6/rpl_iptunnel.c:174)
Read of size 40 at addr ffff888122bf96d8 by task ping6/1543

CPU: 50 UID: 0 PID: 1543 Comm: ping6 Not tainted 6.16.0-rc5-01302-gfadd1e6231b1 #23 PREEMPT(voluntary)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <IRQ>
 dump_stack_lvl (lib/dump_stack.c:122)
 print_report (mm/kasan/report.c:409 mm/kasan/report.c:521)
 kasan_report (mm/kasan/report.c:221 mm/kasan/report.c:636)
 kasan_check_range (mm/kasan/generic.c:175 (discriminator 1) mm/kasan/generic.c:189 (discriminator 1))
 __asan_memmove (mm/kasan/shadow.c:94 (discriminator 2))
 rpl_do_srh_inline.isra.0 (net/ipv6/rpl_iptunnel.c:174)
 rpl_input (net/ipv6/rpl_iptunnel.c:201 net/ipv6/rpl_iptunnel.c:282)
 lwtunnel_input (net/core/lwtunnel.c:459)
 ipv6_rcv (./include/net/dst.h:471 (discriminator 1) ./include/net/dst.h:469 (discriminator 1) net/ipv6/ip6_input.c:79 (discriminator 1) ./include/linux/netfilter.h:317 (discriminator 1) ./include/linux/netfilter.h:311 (discriminator 1) net/ipv6/ip6_input.c:311 (discriminator 1))
 __netif_receive_skb_one_core (net/core/dev.c:5967)
 process_backlog (./include/linux/rcupdate.h:869 net/core/dev.c:6440)
 __napi_poll.constprop.0 (net/core/dev.c:7452)
 net_rx_action (net/core/dev.c:7518 net/core/dev.c:7643)
 handle_softirqs (kernel/softirq.c:579)
 do_softirq (kernel/softirq.c:480 (discriminator 20))
 </IRQ>
 <TASK>
 __local_bh_enable_ip (kernel/softirq.c:407)
 __dev_queue_xmit (net/core/dev.c:4740)
 ip6_finish_output2 (./include/linux/netdevice.h:3358 ./include/net/neighbour.h:526 ./include/net/neighbour.h:540 net/ipv6/ip6_output.c:141)
 ip6_finish_output (net/ipv6/ip6_output.c:215 net/ipv6/ip6_output.c:226)
 ip6_output (./include/linux/netfilter.h:306 net/ipv6/ip6_output.c:248)
 ip6_send_skb (net/ipv6/ip6_output.c:1983)
 rawv6_sendmsg (net/ipv6/raw.c:588 net/ipv6/raw.c:918)
 __sys_sendto (net/socket.c:714 (discriminator 1) net/socket.c:729 (discriminator 1) net/socket.c:2228 (discriminator 1))
 __x64_sys_sendto (net/socket.c:2231)
 do_syscall_64 (arch/x86/entry/syscall_64.c:63 (discriminator 1) arch/x86/entry/syscall_64.c:94 (discriminator 1))
 entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
RIP: 0033:0x7f68cffb2a06
Code: 5d e8 41 8b 93 08 03 00 00 59 5e 48 83 f8 fc 75 19 83 e2 39 83 fa 08 75 11 e8 26 ff ff ff 66 0f 1f 44 00 00 48 8b 45 10 0f 05 <48> 8b 5d f8 c9 c3 0f 1f 40 00 f3 0f 1e fa 55 48 89 e5 48 83 ec 08
RSP: 002b:00007ffefb7c53d0 EFLAGS: 00000202 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 0000564cd69f10a0 RCX: 00007f68cffb2a06
RDX: 0000000000000040 RSI: 0000564cd69f10a4 RDI: 0000000000000003
RBP: 00007ffefb7c53f0 R08: 0000564cd6a032ac R09: 000000000000001c
R10: 0000000000000000 R11: 0000000000000202 R12: 0000564cd69f10a4
R13: 0000000000000040 R14: 00007ffefb7c66e0 R15: 0000564cd69f10a0
 </TASK>

Allocated by task 1543:
 kasan_save_stack (mm/kasan/common.c:48)
 kasan_save_track (mm/kasan/common.c:60 (discriminator 1) mm/kasan/common.c:69 (discriminator 1))
 __kasan_slab_alloc (mm/kasan/common.c:319 mm/kasan/common.c:345)
 kmem_cache_alloc_node_noprof (./include/linux/kasan.h:250 mm/slub.c:4148 mm/slub.c:4197 mm/slub.c:4249)
 kmalloc_reserve (net/core/skbuff.c:581 (discriminator 88))
 __alloc_skb (net/core/skbuff.c:669)
 __ip6_append_data (net/ipv6/ip6_output.c:1672 (discriminator 1))
 ip6_append_data (net/ipv6/ip6_output.c:1859)
 rawv6_sendmsg (net/ipv6/raw.c:911)
 __sys_sendto (net/socket.c:714 (discriminator 1) net/socket.c:729 (discriminator 1) net/socket.c:2228 (discriminator 1))
 __x64_sys_sendto (net/socket.c:2231)
 do_syscall_64 (arch/x86/entry/syscall_64.c:63 (discriminator 1) arch/x86/entry/syscall_64.c:94 (discriminator 1))
 entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)

Freed by task 1543:
 kasan_save_stack (mm/kasan/common.c:48)
 kasan_save_track (mm/kasan/common.c:60 (discriminator 1) mm/kasan/common.c:69 (discriminator 1))
 kasan_save_free_info (mm/kasan/generic.c:579 (discriminator 1))
 __kasan_slab_free (mm/kasan/common.c:271)
 kmem_cache_free (mm/slub.c:4643 (discriminator 3) mm/slub.c:4745 (discriminator 3))
 pskb_expand_head (net/core/skbuff.c:2274)
 rpl_do_srh_inline.isra.0 (net/ipv6/rpl_iptunnel.c:158 (discriminator 1))
 rpl_input (net/ipv6/rpl_iptunnel.c:201 net/ipv6/rpl_iptunnel.c:282)
 lwtunnel_input (net/core/lwtunnel.c:459)
 ipv6_rcv (./include/net/dst.h:471 (discriminator 1) ./include/net/dst.h:469 (discriminator 1) net/ipv6/ip6_input.c:79 (discriminator 1) ./include/linux/netfilter.h:317 (discriminator 1) ./include/linux/netfilter.h:311 (discriminator 1) net/ipv6/ip6_input.c:311 (discriminator 1))
 __netif_receive_skb_one_core (net/core/dev.c:5967)
 process_backlog (./include/linux/rcupdate.h:869 net/core/dev.c:6440)
 __napi_poll.constprop.0 (net/core/dev.c:7452)
 net_rx_action (net/core/dev.c:7518 net/core/dev.c:7643)
 handle_softirqs (kernel/softirq.c:579)
 do_softirq (kernel/softirq.c:480 (discriminator 20))
 __local_bh_enable_ip (kernel/softirq.c:407)
 __dev_queue_xmit (net/core/dev.c:4740)
 ip6_finish_output2 (./include/linux/netdevice.h:3358 ./include/net/neighbour.h:526 ./include/net/neighbour.h:540 net/ipv6/ip6_output.c:141)
 ip6_finish_output (net/ipv6/ip6_output.c:215 net/ipv6/ip6_output.c:226)
 ip6_output (./include/linux/netfilter.h:306 net/ipv6/ip6_output.c:248)
 ip6_send_skb (net/ipv6/ip6_output.c:1983)
 rawv6_sendmsg (net/ipv6/raw.c:588 net/ipv6/raw.c:918)
 __sys_sendto (net/socket.c:714 (discriminator 1) net/socket.c:729 (discriminator 1) net/socket.c:2228 (discriminator 1))
 __x64_sys_sendto (net/socket.c:2231)
 do_syscall_64 (arch/x86/entry/syscall_64.c:63 (discriminator 1) arch/x86/entry/syscall_64.c:94 (discriminator 1))
 entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)

The buggy address belongs to the object at ffff888122bf96c0
 which belongs to the cache skbuff_small_head of size 704
The buggy address is located 24 bytes inside of
 freed 704-byte region [ffff888122bf96c0, ffff888122bf9980)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x122bf8
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0x200000000000040(head|node=0|zone=2)
page_type: f5(slab)
raw: 0200000000000040 ffff888101fc0a00 ffffea000464dc00 0000000000000002
raw: 0000000000000000 0000000080270027 00000000f5000000 0000000000000000
head: 0200000000000040 ffff888101fc0a00 ffffea000464dc00 0000000000000002
head: 0000000000000000 0000000080270027 00000000f5000000 0000000000000000
head: 0200000000000003 ffffea00048afe01 00000000ffffffff 00000000ffffffff
head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888122bf9580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888122bf9600: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>ffff888122bf9680: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
                                                    ^
 ffff888122bf9700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888122bf9780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

The Linux kernel CVE team has assigned CVE-2025-38476 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.7 with commit a7a29f9c361f8542604ef959ae6627f423b7a412 and fixed in 6.1.147 with commit e8101506ab86dd78f823b7028f2036a380f3a12a
	Issue introduced in 5.7 with commit a7a29f9c361f8542604ef959ae6627f423b7a412 and fixed in 6.6.100 with commit 62dcd9d6e61c39122d2f251a26829e2e55b0a11d
	Issue introduced in 5.7 with commit a7a29f9c361f8542604ef959ae6627f423b7a412 and fixed in 6.12.40 with commit 06ec83b6c792fde1f710c1de3e836da6e257c4c4
	Issue introduced in 5.7 with commit a7a29f9c361f8542604ef959ae6627f423b7a412 and fixed in 6.15.8 with commit 034b428aa3583373a5a20b1c5931bb2b3cae1f36
	Issue introduced in 5.7 with commit a7a29f9c361f8542604ef959ae6627f423b7a412 and fixed in 6.16 with commit b640daa2822a39ff76e70200cb2b7b892b896dce

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-38476
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/ipv6/rpl_iptunnel.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/e8101506ab86dd78f823b7028f2036a380f3a12a
	https://git.kernel.org/stable/c/62dcd9d6e61c39122d2f251a26829e2e55b0a11d
	https://git.kernel.org/stable/c/06ec83b6c792fde1f710c1de3e836da6e257c4c4
	https://git.kernel.org/stable/c/034b428aa3583373a5a20b1c5931bb2b3cae1f36
	https://git.kernel.org/stable/c/b640daa2822a39ff76e70200cb2b7b892b896dce