Messages in this thread | | | Date | Sat, 31 Aug 2019 20:07:46 -0400 | From | Sasha Levin <> | Subject | Re: [PATCH 4.14] tcp: fix tcp_rtx_queue_tail in case of empty retransmit queue |
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On Sat, Aug 31, 2019 at 03:14:35PM +0200, Matthieu Baerts wrote: >Hi Sasha, > >Thank you for your reply! > >On 31/08/2019 14:20, Sasha Levin wrote: >> On Sat, Aug 24, 2019 at 08:03:51AM +0200, Tim Froidcoeur wrote: >>> Commit 8c3088f895a0 ("tcp: be more careful in tcp_fragment()") >>> triggers following stack trace: >>> >>> [25244.848046] kernel BUG at ./include/linux/skbuff.h:1406! >>> [25244.859335] RIP: 0010:skb_queue_prev+0x9/0xc >>> [25244.888167] Call Trace: >>> [25244.889182] <IRQ> >>> [25244.890001] tcp_fragment+0x9c/0x2cf >>> [25244.891295] tcp_write_xmit+0x68f/0x988 >>> [25244.892732] __tcp_push_pending_frames+0x3b/0xa0 >>> [25244.894347] tcp_data_snd_check+0x2a/0xc8 >>> [25244.895775] tcp_rcv_established+0x2a8/0x30d >>> [25244.897282] tcp_v4_do_rcv+0xb2/0x158 >>> [25244.898666] tcp_v4_rcv+0x692/0x956 >>> [25244.899959] ip_local_deliver_finish+0xeb/0x169 >>> [25244.901547] __netif_receive_skb_core+0x51c/0x582 >>> [25244.903193] ? inet_gro_receive+0x239/0x247 >>> [25244.904756] netif_receive_skb_internal+0xab/0xc6 >>> [25244.906395] napi_gro_receive+0x8a/0xc0 >>> [25244.907760] receive_buf+0x9a1/0x9cd >>> [25244.909160] ? load_balance+0x17a/0x7b7 >>> [25244.910536] ? vring_unmap_one+0x18/0x61 >>> [25244.911932] ? detach_buf+0x60/0xfa >>> [25244.913234] virtnet_poll+0x128/0x1e1 >>> [25244.914607] net_rx_action+0x12a/0x2b1 >>> [25244.915953] __do_softirq+0x11c/0x26b >>> [25244.917269] ? handle_irq_event+0x44/0x56 >>> [25244.918695] irq_exit+0x61/0xa0 >>> [25244.919947] do_IRQ+0x9d/0xbb >>> [25244.921065] common_interrupt+0x85/0x85 >>> [25244.922479] </IRQ> >>> >>> tcp_rtx_queue_tail() (called by tcp_fragment()) can call >>> tcp_write_queue_prev() on the first packet in the queue, which will >>> trigger >>> the BUG in tcp_write_queue_prev(), because there is no previous packet. >>> >>> This happens when the retransmit queue is empty, for example in case of a >>> zero window. >>> >>> Patch is needed for 4.4, 4.9 and 4.14 stable branches. >> >> There needs to be a better explanation of why it's not needed >> upstream... > >Commit 8c3088f895a0 ("tcp: be more careful in tcp_fragment()") was not a >simple cherry-pick of the original one from master (b617158dc096) >because there is a specific TCP rtx queue only since v4.15. For more >details, please see the commit message of b617158dc096 ("tcp: be more >careful in tcp_fragment()"). > >The BUG() is hit due to the specific code added to versions older than >v4.15. The comment in skb_queue_prev() (include/linux/skbuff.h:1406), >just before the BUG_ON() somehow suggests to add a check before using >it, what Tim did. > >In master, this code path causing the issue will not be taken because >the implementation of tcp_rtx_queue_tail() is different: > > tcp_fragment() → tcp_rtx_queue_tail() → tcp_write_queue_prev() → >skb_queue_prev() → BUG_ON() > >Because this patch is specific to versions older than the two last >stable ones but still linked to the network architecture, who can review >and approve it? :)
Thanks for the explanation. I've changed the commit message to include this explanation and queued it for 4.4, 4.9 and 4.14.
-- Thanks, Sasha
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