When user requests to resolve an output route, the kernel synthesizes
an skb where the relevant parameters (e.g., source address) are set. The
skb is then passed to ip_route_output_key_hash_rcu() which might call
into the flow dissector in case a multipath route was hit and a nexthop
needs to be selected based on the multipath hash.
Since both 'skb->dev' and 'skb->sk' are not set, a warning is triggered
in the flow dissector [1]. The warning is there to prevent codepaths
from silently falling back to the standard flow dissector instead of the
BPF one.
Therefore, instead of removing the warning, set 'skb->dev' to the
loopback device, as its not used for anything but resolving the correct
namespace.
[1]
WARNING: CPU: 1 PID: 24819 at net/core/flow_dissector.c:764 __skb_flow_dissect+0x314/0x16b0
...
RSP: 0018:ffffa0df41fdf650 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8bcded232000 RCX: 0000000000000000
RDX: ffffa0df41fdf7e0 RSI: ffffffff98e415a0 RDI: ffff8bcded232000
RBP: ffffa0df41fdf760 R08: 0000000000000000 R09: 0000000000000000
R10: ffffa0df41fdf7e8 R11: ffff8bcdf27a3000 R12: ffffffff98e415a0
R13: ffffa0df41fdf7e0 R14: ffffffff98dd2980 R15: ffffa0df41fdf7e0
FS: 00007f46f6897680(0000) GS:ffff8bcdf7a80000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055933e95f9a0 CR3: 000000021e636000 CR4: 00000000001006e0
Call Trace:
fib_multipath_hash+0x28c/0x2d0
? fib_multipath_hash+0x28c/0x2d0
fib_select_path+0x241/0x32f
? __fib_lookup+0x6a/0xb0
ip_route_output_key_hash_rcu+0x650/0xa30
? __alloc_skb+0x9b/0x1d0
inet_rtm_getroute+0x3f7/0xb80
? __alloc_pages_nodemask+0x11c/0x2c0
rtnetlink_rcv_msg+0x1d9/0x2f0
? rtnl_calcit.isra.24+0x120/0x120
netlink_rcv_skb+0x54/0x130
rtnetlink_rcv+0x15/0x20
netlink_unicast+0x20a/0x2c0
netlink_sendmsg+0x2d1/0x3d0
sock_sendmsg+0x39/0x50
___sys_sendmsg+0x2a0/0x2f0
? filemap_map_pages+0x16b/0x360
? __handle_mm_fault+0x108e/0x13d0
__sys_sendmsg+0x63/0xa0
? __sys_sendmsg+0x63/0xa0
__x64_sys_sendmsg+0x1f/0x30
do_syscall_64+0x5a/0x120
entry_SYSCALL_64_after_hwframe+0x44/0xa9
Fixes: d0e13a1488 ("flow_dissector: lookup netns by skb->sk if skb->dev is NULL")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
21f9477537