Subject: CVE-2024-49947: net: test for not too small csum_start in virtio_net_hdr_to_skb()

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

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

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

net: test for not too small csum_start in virtio_net_hdr_to_skb()

syzbot was able to trigger this warning [1], after injecting a
malicious packet through af_packet, setting skb->csum_start and thus
the transport header to an incorrect value.

We can at least make sure the transport header is after
the end of the network header (with a estimated minimal size).

[1]
[   67.873027] skb len=4096 headroom=16 headlen=14 tailroom=0
mac=(-1,-1) mac_len=0 net=(16,-6) trans=10
shinfo(txflags=0 nr_frags=1 gso(size=0 type=0 segs=0))
csum(0xa start=10 offset=0 ip_summed=3 complete_sw=0 valid=0 level=0)
hash(0x0 sw=0 l4=0) proto=0x0800 pkttype=0 iif=0
priority=0x0 mark=0x0 alloc_cpu=10 vlan_all=0x0
encapsulation=0 inner(proto=0x0000, mac=0, net=0, trans=0)
[   67.877172] dev name=veth0_vlan feat=0x000061164fdd09e9
[   67.877764] sk family=17 type=3 proto=0
[   67.878279] skb linear:   00000000: 00 00 10 00 00 00 00 00 0f 00 00 00 08 00
[   67.879128] skb frag:     00000000: 0e 00 07 00 00 00 28 00 08 80 1c 00 04 00 00 02
[   67.879877] skb frag:     00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   67.880647] skb frag:     00000020: 00 00 02 00 00 00 08 00 1b 00 00 00 00 00 00 00
[   67.881156] skb frag:     00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   67.881753] skb frag:     00000040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   67.882173] skb frag:     00000050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   67.882790] skb frag:     00000060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   67.883171] skb frag:     00000070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   67.883733] skb frag:     00000080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   67.884206] skb frag:     00000090: 00 00 00 00 00 00 00 00 00 00 69 70 76 6c 61 6e
[   67.884704] skb frag:     000000a0: 31 00 00 00 00 00 00 00 00 00 2b 00 00 00 00 00
[   67.885139] skb frag:     000000b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   67.885677] skb frag:     000000c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   67.886042] skb frag:     000000d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   67.886408] skb frag:     000000e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   67.887020] skb frag:     000000f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   67.887384] skb frag:     00000100: 00 00
[   67.887878] ------------[ cut here ]------------
[   67.887908] offset (-6) >= skb_headlen() (14)
[   67.888445] WARNING: CPU: 10 PID: 2088 at net/core/dev.c:3332 skb_checksum_help (net/core/dev.c:3332 (discriminator 2))
[   67.889353] Modules linked in: macsec macvtap macvlan hsr wireguard curve25519_x86_64 libcurve25519_generic libchacha20poly1305 chacha_x86_64 libchacha poly1305_x86_64 dummy bridge sr_mod cdrom evdev pcspkr i2c_piix4 9pnet_virtio 9p 9pnet netfs
[   67.890111] CPU: 10 UID: 0 PID: 2088 Comm: b363492833 Not tainted 6.11.0-virtme #1011
[   67.890183] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[   67.890309] RIP: 0010:skb_checksum_help (net/core/dev.c:3332 (discriminator 2))
[   67.891043] Call Trace:
[   67.891173]  <TASK>
[   67.891274] ? __warn (kernel/panic.c:741)
[   67.891320] ? skb_checksum_help (net/core/dev.c:3332 (discriminator 2))
[   67.891333] ? report_bug (lib/bug.c:180 lib/bug.c:219)
[   67.891348] ? handle_bug (arch/x86/kernel/traps.c:239)
[   67.891363] ? exc_invalid_op (arch/x86/kernel/traps.c:260 (discriminator 1))
[   67.891372] ? asm_exc_invalid_op (./arch/x86/include/asm/idtentry.h:621)
[   67.891388] ? skb_checksum_help (net/core/dev.c:3332 (discriminator 2))
[   67.891399] ? skb_checksum_help (net/core/dev.c:3332 (discriminator 2))
[   67.891416] ip_do_fragment (net/ipv4/ip_output.c:777 (discriminator 1))
[   67.891448] ? __ip_local_out (./include/linux/skbuff.h:1146 ./include/net/l3mdev.h:196 ./include/net/l3mdev.h:213 net/ipv4/ip_output.c:113)
[   67.891459] ? __pfx_ip_finish_output2 (net/ipv4/ip_output.c:200)
[   67.891470] ? ip_route_output_flow (./arch/x86/include/asm/preempt.h:84 (discriminator 13) ./include/linux/rcupdate.h:96 (discriminator 13) ./include/linux/rcupdate.h:871 (discriminator 13) net/ipv4/route.c:2625 (discriminator 13) ./include/net/route.h:141 (discriminator 13) net/ipv4/route.c:2852 (discriminator 13))
[   67.891484] ipvlan_process_v4_outbound (drivers/net/ipvlan/ipvlan_core.c:445 (discriminator 1))
[   67.891581] ipvlan_queue_xmit (drivers/net/ipvlan/ipvlan_core.c:542 drivers/net/ipvlan/ipvlan_core.c:604 drivers/net/ipvlan/ipvlan_core.c:670)
[   67.891596] ipvlan_start_xmit (drivers/net/ipvlan/ipvlan_main.c:227)
[   67.891607] dev_hard_start_xmit (./include/linux/netdevice.h:4916 ./include/linux/netdevice.h:4925 net/core/dev.c:3588 net/core/dev.c:3604)
[   67.891620] __dev_queue_xmit (net/core/dev.h:168 (discriminator 25) net/core/dev.c:4425 (discriminator 25))
[   67.891630] ? skb_copy_bits (./include/linux/uaccess.h:233 (discriminator 1) ./include/linux/uaccess.h:260 (discriminator 1) ./include/linux/highmem-internal.h:230 (discriminator 1) net/core/skbuff.c:3018 (discriminator 1))
[   67.891645] ? __pskb_pull_tail (net/core/skbuff.c:2848 (discriminator 4))
[   67.891655] ? skb_partial_csum_set (net/core/skbuff.c:5657)
[   67.891666] ? virtio_net_hdr_to_skb.constprop.0 (./include/linux/skbuff.h:2791 (discriminator 3) ./include/linux/skbuff.h:2799 (discriminator 3) ./include/linux/virtio_net.h:109 (discriminator 3))
[   67.891684] packet_sendmsg (net/packet/af_packet.c:3145 (discriminator 1) net/packet/af_packet.c:3177 (discriminator 1))
[   67.891700] ? _raw_spin_lock_bh (./arch/x86/include/asm/atomic.h:107 (discriminator 4) ./include/linux/atomic/atomic-arch-fallback.h:2170 (discriminator 4) ./include/linux/atomic/atomic-instrumented.h:1302 (discriminator 4) ./include/asm-generic/qspinlock.h:111 (discriminator 4) ./include/linux/spinlock.h:187 (discriminator 4) ./include/linux/spinlock_api_smp.h:127 (discriminator 4) kernel/locking/spinlock.c:178 (discriminator 4))
[   67.891716] __sys_sendto (net/socket.c:730 (discriminator 1) net/socket.c:745 (discriminator 1) net/socket.c:2210 (discriminator 1))
[   67.891734] ? do_sock_setsockopt (net/socket.c:2335)
[   67.891747] ? __sys_setsockopt (./include/linux/file.h:34 net/socket.c:2355)
[   67.891761] __x64_sys_sendto (net/socket.c:2222 (discriminator 1) net/socket.c:2218 (discriminator 1) net/socket.c:2218 (discriminator 1))
[   67.891772] do_syscall_64 (arch/x86/entry/common.c:52 (discriminator 1) arch/x86/entry/common.c:83 (discriminator 1))
[   67.891785] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)

The Linux kernel CVE team has assigned CVE-2024-49947 to this issue.

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

	Issue introduced in 6.6.14 with commit 342c88f406c2 and fixed in 6.6.55 with commit d9dfd41e32cc
	Issue introduced in 6.8 with commit 9181d6f8a2bb and fixed in 6.10.14 with commit 4cc0648e9e32
	Issue introduced in 6.8 with commit 9181d6f8a2bb and fixed in 6.11.3 with commit 7711c419a915
	Issue introduced in 6.8 with commit 9181d6f8a2bb and fixed in 6.12-rc2 with commit 49d14b54a527
	Issue introduced in 6.7.2 with commit 765290b628c2

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-2024-49947
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:
	include/linux/virtio_net.h

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/d9dfd41e32ccc5198033ddd1ff1516822dfefa5a
	https://git.kernel.org/stable/c/4cc0648e9e3240496835dc698ace1d046d8d57ea
	https://git.kernel.org/stable/c/7711c419a915ee0dd91c125d2b967bbf2a72e9ac
	https://git.kernel.org/stable/c/49d14b54a527289d09a9480f214b8c586322310a