Re: [PATCH net-next 1/2] net: Fix skb consume leak in sch_handle_egress

[Simon Horman <horms@kernel.org>]

On Fri, Aug 25, 2023 at 03:49:45PM +0200, Daniel Borkmann wrote:
> Fix a memory leak for the tc egress path with TC_ACT_{STOLEN,QUEUED,TRAP}:
> 
>   [...]
>   unreferenced object 0xffff88818bcb4f00 (size 232):
>   comm "softirq", pid 0, jiffies 4299085078 (age 134.028s)
>   hex dump (first 32 bytes):
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>     00 80 70 61 81 88 ff ff 00 41 31 14 81 88 ff ff  ..pa.....A1.....
>   backtrace:
>     [<ffffffff9991b938>] kmem_cache_alloc_node+0x268/0x400
>     [<ffffffff9b3d9231>] __alloc_skb+0x211/0x2c0
>     [<ffffffff9b3f0c7e>] alloc_skb_with_frags+0xbe/0x6b0
>     [<ffffffff9b3bf9a9>] sock_alloc_send_pskb+0x6a9/0x870
>     [<ffffffff9b6b3f00>] __ip_append_data+0x14d0/0x3bf0
>     [<ffffffff9b6ba24e>] ip_append_data+0xee/0x190
>     [<ffffffff9b7e1496>] icmp_push_reply+0xa6/0x470
>     [<ffffffff9b7e4030>] icmp_reply+0x900/0xa00
>     [<ffffffff9b7e42e3>] icmp_echo.part.0+0x1a3/0x230
>     [<ffffffff9b7e444d>] icmp_echo+0xcd/0x190
>     [<ffffffff9b7e9566>] icmp_rcv+0x806/0xe10
>     [<ffffffff9b699bd1>] ip_protocol_deliver_rcu+0x351/0x3d0
>     [<ffffffff9b699f14>] ip_local_deliver_finish+0x2b4/0x450
>     [<ffffffff9b69a234>] ip_local_deliver+0x174/0x1f0
>     [<ffffffff9b69a4b2>] ip_sublist_rcv_finish+0x1f2/0x420
>     [<ffffffff9b69ab56>] ip_sublist_rcv+0x466/0x920
>   [...]
> 
> I was able to reproduce this via:
> 
>   ip link add dev dummy0 type dummy
>   ip link set dev dummy0 up
>   tc qdisc add dev eth0 clsact
>   tc filter add dev eth0 egress protocol ip prio 1 u32 match ip protocol 1 0xff action mirred egress redirect dev dummy0
>   ping 1.1.1.1
>   <stolen>
> 
> After the fix, there are no kmemleak reports with the reproducer. This is
> in line with what is also done on the ingress side, and from debugging the
> skb_unref(skb) on dummy xmit and sch_handle_egress() side, it is visible
> that these are two different skbs with both skb_unref(skb) as true. The two
> seen skbs are due to mirred doing a skb_clone() internally as use_reinsert
> is false in tcf_mirred_act() for egress. This was initially reported by Gal.
> 
> Fixes: e420bed02507 ("bpf: Add fd-based tcx multi-prog infra with link support")
> Reported-by: Gal Pressman <gal@nvidia.com>
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> Link: https://lore.kernel.org/bpf/bdfc2640-8f65-5b56-4472-db8e2b161aab@nvidia.com

Reviewed-by: Simon Horman <horms@kernel.org>