On 04/13/2018 05:39 PM, Subash Abhinov Kasiviswanathan wrote:
> We are seeing a warning followed by a crash on an ARM64 device with
> Android 4.14 based kernel.
>
> It looks like both sk->sk_write_queue and sk->sk_send_head are NULL.
> Since the sk->sk_write_queue is NULL and is dereferenced in tcp_rto_delta_us()
> to get the skb->skb_mstamp, there is crash observed.
>
> Since this is 4.14.32, it already has commit ("tcp: reset sk_send_head in
> tcp_write_queue_purge")
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?h=v4.14.34&id=dbbf2d1e4077bab0c65ece2765d3fc69cf7d610f
>
> 12876.013077: <6> WARNING: CPU: 5 PID: 14828 at net/ipv4/tcp_output.c:2469
> tcp_send_loss_probe+0x198/0x1b8
> 12876.038939: <6> task: ffffffe73f7e5a80 task.stack: ffffff801b068000
> 12876.038941: <2> PC is at tcp_send_loss_probe+0x198/0x1b8
> 12876.038942: <2> LR is at tcp_send_loss_probe+0x28/0x1b8
> 12876.038944: <2> pc : [<ffffff8dc8db16f8>] lr : [<ffffff8dc8db1588>]
> pstate: 60400145
> 12876.038944: <2> sp : ffffff800802bd30
> 12876.038945: <2> x29: ffffff800802bd50 x28: ffffff8dc9d83eb8
> 12876.038948: <2> x27: ffffff800802be08 x26: ffffff8dc9737000
> 12876.038950: <2> x25: 0000000000000001 x24: ffffffe744ea1728
> 12876.038952: <2> x23: ffffffe73f7e5a80 x22: 0000000000000558
> 12876.038954: <2> x21: 0000000000000000 x20: 0000000001080020
> 12876.038956: <2> x19: ffffffe73d06e440 x18: 0000000000000020
> 12876.038958: <2> x17: 0000000000000014 x16: 0000000000000030
> 12876.038960: <2> x15: 0000000000000000 x14: 0000000000000000
> 12876.038962: <2> x13: 0000000013af314c x12: 0000002773f8a550
> 12876.038965: <2> x11: 0000000000000538 x10: 0000000000000000
> 12876.038967: <2> x9 : 0000000000000020 x8 : ffffffe73d06e5f0
> 12876.038969: <2> x7 : 0000000000924278 x6 : ffffffe76fe9ed80
> 12876.038971: <2> x5 : ffffffe76fe9ed80 x4 : 000000000f500458
> 12876.038973: <2> x3 : ffffff800802bce0 x2 : ffffff800802bce8
> 12876.038975: <2> x1 : 0000000000000000 x0 : 0000000000000558
> 12876.039082: <2> [<ffffff8dc8db16f8>] tcp_send_loss_probe+0x198/0x1b8
> 12876.039084: <2> [<ffffff8dc8db6698>] tcp_write_timer_handler+0xf8/0x1c4
> 12876.039086: <2> [<ffffff8dc8db68cc>] tcp_write_timer+0x5c/0x98
> 12876.039089: <2> [<ffffff8dc8144f10>] call_timer_fn+0xc0/0x1b4
> 12876.039091: <2> [<ffffff8dc8143f68>] run_timer_softirq+0x230/0x850
> 12876.039094: <2> [<ffffff8dc8081b74>] __do_softirq+0x1dc/0x3a4
> 12876.039096: <2> [<ffffff8dc80b8fec>] irq_exit+0xc8/0xd4
> 12876.039098: <2> [<ffffff8dc812a004>] __handle_domain_irq+0x8c/0xc4
> 12876.039099: <2> [<ffffff8dc8081940>] gic_handle_irq+0x164/0x1bc
>
> [net/ipv4/tcp_output.c]
> void tcp_send_loss_probe(struct sock *sk)
> {
> struct tcp_sock *tp = tcp_sk(sk);
> struct sk_buff *skb;
> int pcount;
> int mss = tcp_current_mss(sk);
>
> ...
>
> /* Retransmit last segment. */
> if (WARN_ON(!skb))
> goto rearm_timer;
>
> 12876.043967: <6> Unable to handle kernel NULL pointer dereference at
> virtual address 00000010
> 12876.091600: <6> Internal error: Oops: 96000005 [#1] PREEMPT SMP
> 12876.152597: <2> PC is at tcp_rearm_rto+0x48/0x90
> 12876.156979: <2> LR is at tcp_send_loss_probe+0x178/0x1b8
> 12876.162077: <2> pc : [<ffffff8dc8da76c4>] lr : [<ffffff8dc8db16d8>]
> pstate: 60400145
> 12876.169657: <2> sp : ffffff800802bd10
> 12876.173056: <2> x29: ffffff800802bd20 x28: ffffff8dc9d83eb8
> 12876.178511: <2> x27: ffffff800802be08 x26: ffffff8dc9737000
> 12876.183967: <2> x25: 0000000000000001 x24: ffffffe744ea1728
> 12876.189418: <2> x23: ffffffe73f7e5a80 x22: 0000000000000558
> 12876.194863: <2> x21: 0000000000000000 x20: 0000000001080020
> 12876.200312: <2> x19: ffffffe73d06e440 x18: 0000000000000020
> 12876.205758: <2> x17: 0000000000000014 x16: 0000000000000030
> 12876.211212: <2> x15: 0000000000000000 x14: 0000000000000000
> 12876.216660: <2> x13: 0000000013af314c x12: 0000002773f8a550
> 12876.222108: <2> x11: 0000000000000538 x10: 0000000000000000
> 12876.227561: <2> x9 : 0000000000000000 x8 : ffffffe73d06e5f0
> 12876.233008: <2> x7 : 0000000000924278 x6 : ffffffe76fe9ed80
> 12876.238455: <2> x5 : ffffffe76fe9ed80 x4 : 000000000f500458
> 12876.243907: <2> x3 : ffffff800802bce0 x2 : ffffff800802bce8
> 12876.249360: <2> x1 : 0000000000000000 x0 : 0000000000000867
> 12876.473522: <2> [<ffffff8dc8da76c4>] tcp_rearm_rto+0x48/0x90
> 12876.478971: <2> [<ffffff8dc8db16d8>] tcp_send_loss_probe+0x178/0x1b8
> 12876.485131: <2> [<ffffff8dc8db6698>] tcp_write_timer_handler+0xf8/0x1c4
> 12876.491557: <2> [<ffffff8dc8db68cc>] tcp_write_timer+0x5c/0x98
> 12876.497189: <2> [<ffffff8dc8144f10>] call_timer_fn+0xc0/0x1b4
> 12876.502731: <2> [<ffffff8dc8143f68>] run_timer_softirq+0x230/0x850
> 12876.508716: <2> [<ffffff8dc8081b74>] __do_softirq+0x1dc/0x3a4
> 12876.514260: <2> [<ffffff8dc80b8fec>] irq_exit+0xc8/0xd4
> 12876.519261: <2> [<ffffff8dc812a004>] __handle_domain_irq+0x8c/0xc4
> 12876.525245: <2> [<ffffff8dc8081940>] gic_handle_irq+0x164/0x1bc
>
> [net/ipv4/tcp_input.c]
> void tcp_rearm_rto(struct sock *sk)
> {
> ...
> inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
> } else {
> u32 rto = inet_csk(sk)->icsk_rto;
> /* Offset the time elapsed after installing regular RTO */
> if (icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
> icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
> s64 delta_us = tcp_rto_delta_us(sk);
> /* delta_us may not be positive if the socket is locked
> * when the retrans timer fires and is rescheduled.
> */
> rto = usecs_to_jiffies(max_t(int, delta_us, 1));
>
>
> [include/net/tcp.h]
> static inline s64 tcp_rto_delta_us(const struct sock *sk)
> {
> const struct sk_buff *skb = tcp_write_queue_head(sk);
> u32 rto = inet_csk(sk)->icsk_rto;
> u64 rto_time_stamp_us = skb->skb_mstamp + jiffies_to_usecs(rto);
>
> return rto_time_stamp_us - tcp_sk(sk)->tcp_mstamp;
> }
>
We probably need to clear tp->packets_out :/
