Subject: CVE-2024-26641: ip6_tunnel: make sure to pull inner header in __ip6_tnl_rcv()

From: Greg Kroah-Hartman <[email-masked]>

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

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

ip6_tunnel: make sure to pull inner header in __ip6_tnl_rcv()

syzbot found __ip6_tnl_rcv() could access unitiliazed data [1].

Call pskb_inet_may_pull() to fix this, and initialize ipv6h
variable after this call as it can change skb->head.

[1]
 BUG: KMSAN: uninit-value in __INET_ECN_decapsulate include/net/inet_ecn.h:253 [inline]
 BUG: KMSAN: uninit-value in INET_ECN_decapsulate include/net/inet_ecn.h:275 [inline]
 BUG: KMSAN: uninit-value in IP6_ECN_decapsulate+0x7df/0x1e50 include/net/inet_ecn.h:321
  __INET_ECN_decapsulate include/net/inet_ecn.h:253 [inline]
  INET_ECN_decapsulate include/net/inet_ecn.h:275 [inline]
  IP6_ECN_decapsulate+0x7df/0x1e50 include/net/inet_ecn.h:321
  ip6ip6_dscp_ecn_decapsulate+0x178/0x1b0 net/ipv6/ip6_tunnel.c:727
  __ip6_tnl_rcv+0xd4e/0x1590 net/ipv6/ip6_tunnel.c:845
  ip6_tnl_rcv+0xce/0x100 net/ipv6/ip6_tunnel.c:888
 gre_rcv+0x143f/0x1870
  ip6_protocol_deliver_rcu+0xda6/0x2a60 net/ipv6/ip6_input.c:438
  ip6_input_finish net/ipv6/ip6_input.c:483 [inline]
  NF_HOOK include/linux/netfilter.h:314 [inline]
  ip6_input+0x15d/0x430 net/ipv6/ip6_input.c:492
  ip6_mc_input+0xa7e/0xc80 net/ipv6/ip6_input.c:586
  dst_input include/net/dst.h:461 [inline]
  ip6_rcv_finish+0x5db/0x870 net/ipv6/ip6_input.c:79
  NF_HOOK include/linux/netfilter.h:314 [inline]
  ipv6_rcv+0xda/0x390 net/ipv6/ip6_input.c:310
  __netif_receive_skb_one_core net/core/dev.c:5532 [inline]
  __netif_receive_skb+0x1a6/0x5a0 net/core/dev.c:5646
  netif_receive_skb_internal net/core/dev.c:5732 [inline]
  netif_receive_skb+0x58/0x660 net/core/dev.c:5791
  tun_rx_batched+0x3ee/0x980 drivers/net/tun.c:1555
  tun_get_user+0x53af/0x66d0 drivers/net/tun.c:2002
  tun_chr_write_iter+0x3af/0x5d0 drivers/net/tun.c:2048
  call_write_iter include/linux/fs.h:2084 [inline]
  new_sync_write fs/read_write.c:497 [inline]
  vfs_write+0x786/0x1200 fs/read_write.c:590
  ksys_write+0x20f/0x4c0 fs/read_write.c:643
  __do_sys_write fs/read_write.c:655 [inline]
  __se_sys_write fs/read_write.c:652 [inline]
  __x64_sys_write+0x93/0xd0 fs/read_write.c:652
  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
  do_syscall_64+0x6d/0x140 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

Uninit was created at:
  slab_post_alloc_hook+0x129/0xa70 mm/slab.h:768
  slab_alloc_node mm/slub.c:3478 [inline]
  kmem_cache_alloc_node+0x5e9/0xb10 mm/slub.c:3523
  kmalloc_reserve+0x13d/0x4a0 net/core/skbuff.c:560
  __alloc_skb+0x318/0x740 net/core/skbuff.c:651
  alloc_skb include/linux/skbuff.h:1286 [inline]
  alloc_skb_with_frags+0xc8/0xbd0 net/core/skbuff.c:6334
  sock_alloc_send_pskb+0xa80/0xbf0 net/core/sock.c:2787
  tun_alloc_skb drivers/net/tun.c:1531 [inline]
  tun_get_user+0x1e8a/0x66d0 drivers/net/tun.c:1846
  tun_chr_write_iter+0x3af/0x5d0 drivers/net/tun.c:2048
  call_write_iter include/linux/fs.h:2084 [inline]
  new_sync_write fs/read_write.c:497 [inline]
  vfs_write+0x786/0x1200 fs/read_write.c:590
  ksys_write+0x20f/0x4c0 fs/read_write.c:643
  __do_sys_write fs/read_write.c:655 [inline]
  __se_sys_write fs/read_write.c:652 [inline]
  __x64_sys_write+0x93/0xd0 fs/read_write.c:652
  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
  do_syscall_64+0x6d/0x140 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

CPU: 0 PID: 5034 Comm: syz-executor331 Not tainted 6.7.0-syzkaller-00562-g9f8413c4a66f #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023

The Linux kernel CVE team has assigned CVE-2024-26641 to this issue.

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

	Issue introduced in 4.7 with commit 0d3c703a9d17 and fixed in 5.10.210 with commit a9bc32879a08
	Issue introduced in 4.7 with commit 0d3c703a9d17 and fixed in 5.15.149 with commit af6b5c50d47a
	Issue introduced in 4.7 with commit 0d3c703a9d17 and fixed in 6.1.77 with commit d54e4da98bbf
	Issue introduced in 4.7 with commit 0d3c703a9d17 and fixed in 6.6.16 with commit 350a6640fac4
	Issue introduced in 4.7 with commit 0d3c703a9d17 and fixed in 6.7.4 with commit c835df3bcc14
	Issue introduced in 4.7 with commit 0d3c703a9d17 and fixed in 6.8 with commit 8d975c15c0cd

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-2024-26641
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/ip6_tunnel.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/a9bc32879a08f23cdb80a48c738017e39aea1080
	https://git.kernel.org/stable/c/af6b5c50d47ab43e5272ad61935d0ed2e264d3f0
	https://git.kernel.org/stable/c/d54e4da98bbfa8c257bdca94c49652d81d18a4d8
	https://git.kernel.org/stable/c/350a6640fac4b53564ec20aa3f4a0922cb0ba5e6
	https://git.kernel.org/stable/c/c835df3bcc14858ae9b27315dd7de76370b94f3a
	https://git.kernel.org/stable/c/8d975c15c0cd744000ca386247432d57b21f9df0