[PATCH 0/2] net/af_packet: Fix kernel BUG in __skb_gso_segment

[Tudor Ambarus]

The series is intended for sta...@vger.kernel.org # 5.4+

Syzkaller reported the following bug on linux-5.{4, 10, 15}.y:
https://syzkaller.appspot.com/bug?id=ce5575575f074c33ff80d104f5baee26f22e95f5

The upstream commit that introduces this bug is:
1ed1d5921139 ("net: skip virtio_net_hdr_set_proto if protocol already set")

Upstream fixes the bug with the following commits, one of which introduces
new support:
e9d3f80935b6 ("net/af_packet: make sure to pull mac header")
dfed913e8b55 ("net/af_packet: add VLAN support for AF_PACKET SOCK_RAW GSO")

The additional logic and risk backported seems manageable.

The blammed commit introduces a kernel BUG in __skb_gso_segment for
AF_PACKET SOCK_RAW GSO VLAN tagged packets. What happens is that
virtio_net_hdr_set_proto() exists early as skb->protocol is already set to
ETH_P_ALL. Then in packet_parse_headers() skb->protocol is set to
ETH_P_8021AD, but neither the network header position is adjusted, nor the
mac header is pulled. Thus when we get to validate the xmit skb and enter
skb_mac_gso_segment(), skb->mac_len has value 14, but vlan_depth gets
updated to 18 after skb_network_protocol() is called. This causes the
BUG_ON from __skb_pull(skb, vlan_depth) to be hit, as the mac header has
not been pulled yet.

The fixes from upstream backported cleanly without conflicts. I updated
the commit message of the first patch to describe the problem encountered,
and added Cc, Fixes, Reported-by and Tested-by tags. For the second patch
I just added Cc to stable indicating the versions to be fixed, and added
my Tested and Signed-off-by tags.

I tested the patches on linux-5.{4, 10, 15}.y.

Eric Dumazet (1):
net/af_packet: make sure to pull mac header

Hangbin Liu (1):
net/af_packet: add VLAN support for AF_PACKET SOCK_RAW GSO

net/packet/af_packet.c | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)

--
2.34.1

[Tudor Ambarus]

From: Hangbin Liu <liuha...@gmail.com>

[ Upstream commit dfed913e8b55a0c2c4906f1242fd38fd9a116e49 ]

Before the blammed commit, the kernel drops GSO VLAN tagged packet if it's
created with socket(AF_PACKET, SOCK_RAW, 0) plus virtio_net_hdr.
The reason is AF_PACKET doesn't adjust the skb network header if there is
a VLAN tag. Then after virtio_net_hdr_set_proto() called, the skb->protocol
will be set to ETH_P_IP/IPv6. And in later inet/ipv6_gso_segment() the skb
is dropped as network header position is invalid.

The blammed commit introduces a kernel BUG in __skb_gso_segment for
AF_PACKET SOCK_RAW GSO VLAN tagged packets. What happens is that
virtio_net_hdr_set_proto() exists early as skb->protocol is already set to
ETH_P_ALL. Then in packet_parse_headers() skb->protocol is set to
ETH_P_8021AD, but neither the network header position is adjusted, nor the
mac header is pulled. Thus when we get to validate the xmit skb and enter
skb_mac_gso_segment(), skb->mac_len has value 14, but vlan_depth gets
updated to 18 after skb_network_protocol() is called. This causes the
BUG_ON from __skb_pull(skb, vlan_depth) to be hit, as the mac header has
not been pulled yet.

Let's handle VLAN packets by adjusting network header position in
packet_parse_headers(). The adjustment is safe and does not affect the
later xmit as tap device also did that. The mac header pull is handled in
a following commit:
commit e9d3f80935b6 ("net/af_packet: make sure to pull mac header")

In packet_snd(), packet_parse_headers() need to be moved before calling
virtio_net_hdr_set_proto(), so we can set correct skb->protocol and
network header first.

There is no need to update tpacket_snd() as it calls packet_parse_headers()
in tpacket_fill_skb(), which is already before calling virtio_net_hdr_*
functions.

skb->no_fcs setting is also moved upper to make all skb settings together
and keep consistency with function packet_sendmsg_spkt().

Cc: sta...@vger.kernel.org # 5.4+
Fixes: 1ed1d5921139 ("net: skip virtio_net_hdr_set_proto if protocol already set")
Reported-by: syzbot+3d91b8...@syzkaller.appspotmail.com
Signed-off-by: Hangbin Liu <liuha...@gmail.com>
Acked-by: Willem de Bruijn <wil...@google.com>
Acked-by: Michael S. Tsirkin <m...@redhat.com>
Link: https://lore.kernel.org/r/20220425014502.98...@gmail.com
Signed-off-by: Paolo Abeni <pab...@redhat.com>
Tested-by: Tudor Ambarus <tudor....@linaro.org>
[ta: Update commit description, add Cc, Fixes, Reported-by and Tested-by.]
Signed-off-by: Tudor Ambarus <tudor....@linaro.org>
---
net/packet/af_packet.c | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index ceca0d6c41b5..f25fa75fe651 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1888,12 +1888,20 @@ static int packet_rcv_spkt(struct sk_buff *skb, struct net_device *dev,

static void packet_parse_headers(struct sk_buff *skb, struct socket *sock)
{
+ int depth;
+
if ((!skb->protocol || skb->protocol == htons(ETH_P_ALL)) &&
sock->type == SOCK_RAW) {
skb_reset_mac_header(skb);
skb->protocol = dev_parse_header_protocol(skb);
}

+ /* Move network header to the right position for VLAN tagged packets */
+ if (likely(skb->dev->type == ARPHRD_ETHER) &&
+ eth_type_vlan(skb->protocol) &&
+ __vlan_get_protocol(skb, skb->protocol, &depth) != 0)
+ skb_set_network_header(skb, depth);
+
skb_probe_transport_header(skb);
}

@@ -3008,6 +3016,11 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
skb->mark = sockc.mark;
skb->tstamp = sockc.transmit_time;

+ if (unlikely(extra_len == 4))
+ skb->no_fcs = 1;
+
+ packet_parse_headers(skb, sock);
+
if (has_vnet_hdr) {
err = virtio_net_hdr_to_skb(skb, &vnet_hdr, vio_le());
if (err)
@@ -3016,11 +3029,6 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
virtio_net_hdr_set_proto(skb, &vnet_hdr);
}

- packet_parse_headers(skb, sock);
-
- if (unlikely(extra_len == 4))
- skb->no_fcs = 1;
-
err = po->xmit(skb);
if (unlikely(err != 0)) {
if (err > 0)
--
2.34.1

[Tudor Ambarus]

From: Eric Dumazet <edum...@google.com>

[ Upstream commit e9d3f80935b6607dcdc5682b00b1d4b28e0a0c5d ]

GSO assumes skb->head contains link layer headers.

tun device in some case can provide base 14 bytes,
regardless of VLAN being used or not.

After blamed commit, we can end up setting a network
header offset of 18+, we better pull the missing
bytes to avoid a posible crash in GSO.

syzbot report was:
kernel BUG at include/linux/skbuff.h:2699!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 3601 Comm: syz-executor210 Not tainted 5.18.0-syzkaller-11338-g2c5ca23f7414 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:__skb_pull include/linux/skbuff.h:2699 [inline]
RIP: 0010:skb_mac_gso_segment+0x48f/0x530 net/core/gro.c:136
Code: 00 48 c7 c7 00 96 d4 8a c6 05 cb d3 45 06 01 e8 26 bb d0 01 e9 2f fd ff ff 49 c7 c4 ea ff ff ff e9 f1 fe ff ff e8 91 84 19 fa <0f> 0b 48 89 df e8 97 44 66 fa e9 7f fd ff ff e8 ad 44 66 fa e9 48
RSP: 0018:ffffc90002e2f4b8 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000012 RCX: 0000000000000000
RDX: ffff88805bb58000 RSI: ffffffff8760ed0f RDI: 0000000000000004
RBP: 0000000000005dbc R08: 0000000000000004 R09: 0000000000000fe0
R10: 0000000000000fe4 R11: 0000000000000000 R12: 0000000000000fe0
R13: ffff88807194d780 R14: 1ffff920005c5e9b R15: 0000000000000012
FS: 000055555730f300(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000200015c0 CR3: 0000000071ff8000 CR4: 0000000000350ee0
Call Trace:
<TASK>
__skb_gso_segment+0x327/0x6e0 net/core/dev.c:3411
skb_gso_segment include/linux/netdevice.h:4749 [inline]
validate_xmit_skb+0x6bc/0xf10 net/core/dev.c:3669
validate_xmit_skb_list+0xbc/0x120 net/core/dev.c:3719
sch_direct_xmit+0x3d1/0xbe0 net/sched/sch_generic.c:327
__dev_xmit_skb net/core/dev.c:3815 [inline]
__dev_queue_xmit+0x14a1/0x3a00 net/core/dev.c:4219
packet_snd net/packet/af_packet.c:3071 [inline]
packet_sendmsg+0x21cb/0x5550 net/packet/af_packet.c:3102
sock_sendmsg_nosec net/socket.c:714 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:734
____sys_sendmsg+0x6eb/0x810 net/socket.c:2492
___sys_sendmsg+0xf3/0x170 net/socket.c:2546
__sys_sendmsg net/socket.c:2575 [inline]
__do_sys_sendmsg net/socket.c:2584 [inline]
__se_sys_sendmsg net/socket.c:2582 [inline]
__x64_sys_sendmsg+0x132/0x220 net/socket.c:2582
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x46/0xb0
RIP: 0033:0x7f4b95da06c9
Code: 28 c3 e8 4a 15 00 00 66 2e 0f 1f 84 00 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd7defc4c8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007ffd7defc4f0 RCX: 00007f4b95da06c9
RDX: 0000000000000000 RSI: 0000000020000140 RDI: 0000000000000003
RBP: 0000000000000003 R08: bb1414ac00000050 R09: bb1414ac00000050
R10: 0000000000000004 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffd7defc4e0 R14: 00007ffd7defc4d8 R15: 00007ffd7defc4d4
</TASK>

Cc: sta...@vger.kernel.org # 5.4+
Fixes: dfed913e8b55 ("net/af_packet: add VLAN support for AF_PACKET SOCK_RAW GSO")
Signed-off-by: Eric Dumazet <edum...@google.com>
Reported-by: syzbot <syzk...@googlegroups.com>
Acked-by: Hangbin Liu <liuha...@gmail.com>

Acked-by: Willem de Bruijn <wil...@google.com>

Cc: Michael S. Tsirkin <m...@redhat.com>
Signed-off-by: Jakub Kicinski <ku...@kernel.org>
Tested-by: Tudor Ambarus <tudor....@linaro.org>

Signed-off-by: Tudor Ambarus <tudor....@linaro.org>
---

net/packet/af_packet.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index f25fa75fe651..7f9f2d0ef0e6 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1899,8 +1899,10 @@ static void packet_parse_headers(struct sk_buff *skb, struct socket *sock)

/* Move network header to the right position for VLAN tagged packets */

if (likely(skb->dev->type == ARPHRD_ETHER) &&

eth_type_vlan(skb->protocol) &&
- __vlan_get_protocol(skb, skb->protocol, &depth) != 0)
- skb_set_network_header(skb, depth);

+ __vlan_get_protocol(skb, skb->protocol, &depth) != 0) {

+ if (pskb_may_pull(skb, depth))

+ skb_set_network_header(skb, depth);
+ }

skb_probe_transport_header(skb);
}

--
2.34.1

[Greg KH]

Now queued up, thanks.

greg k-h