RE: [PATCH RESEND bpf 1/4] bpf, sockmap: Fix repeated calls to sock_put() when msg has more_data

John Fastabend
2022-11-23T02:50:55Z

Pengcheng Yang wrote:
> In tcp_bpf_send_verdict() redirection, the eval variable is assigned to
> __SK_REDIRECT after the apply_bytes data is sent, if msg has more_data,
> sock_put() will be called multiple times.
> We should reset the eval variable to __SK_NONE every time more_data
> starts.
>
> This causes:
>
> IPv4: Attempt to release TCP socket in state 1 00000000b4c925d7
> ------------[ cut here ]------------
> refcount_t: addition on 0; use-after-free.
> WARNING: CPU: 5 PID: 4482 at lib/refcount.c:25 refcount_warn_saturate+0x7d/0x110
> Modules linked in:
> CPU: 5 PID: 4482 Comm: sockhash_bypass Kdump: loaded Not tainted 6.0.0 #1
> Hardware name: Red Hat KVM, BIOS 1.11.0-2.el7 04/01/2014
> Call Trace:
> <TASK>
> __tcp_transmit_skb+0xa1b/0xb90
> ? __alloc_skb+0x8c/0x1a0
> ? __kmalloc_node_track_caller+0x184/0x320
> tcp_write_xmit+0x22a/0x1110
> __tcp_push_pending_frames+0x32/0xf0
> do_tcp_sendpages+0x62d/0x640
> tcp_bpf_push+0xae/0x2c0
> tcp_bpf_sendmsg_redir+0x260/0x410
> ? preempt_count_add+0x70/0xa0
> tcp_bpf_send_verdict+0x386/0x4b0
> tcp_bpf_sendmsg+0x21b/0x3b0
> sock_sendmsg+0x58/0x70
> __sys_sendto+0xfa/0x170
> ? xfd_validate_state+0x1d/0x80
> ? switch_fpu_return+0x59/0xe0
> __x64_sys_sendto+0x24/0x30
> do_syscall_64+0x37/0x90
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> Fixes: cd9733f5d75c ("tcp_bpf: Fix one concurrency problem in the tcp_bpf_send_verdict function")
> Signed-off-by: Pengcheng Yang <yangpc@wangsu.com>

Thanks.

Acked-by: John Fastabend <john.fastabend@gmail.com>