xdp: fix page_pool leaks #6200
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xdp: fix page_pool leaks #6200
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Currently, generic XDP hook uses xdp_rxq_info from netstack Rx queues which do not have its XDP memory model registered. There is a case when XDP program calls bpf_xdp_adjust_tail() BPF helper, which in turn releases underlying memory. This happens when it consumes enough amount of bytes and when XDP buffer has fragments. For this action the memory model knowledge passed to XDP program is crucial so that core can call suitable function for freeing/recycling the page. For netstack queues it defaults to MEM_TYPE_PAGE_SHARED (0) due to lack of mem model registration. The problem we're fixing here is when kernel copied the skb to new buffer backed by system's page_pool and XDP buffer is built around it. Then when bpf_xdp_adjust_tail() calls __xdp_return(), it acts incorrectly due to mem type not being set to MEM_TYPE_PAGE_POOL and causes a page leak. Pull out the existing code from bpf_prog_run_generic_xdp() that init/prepares xdp_buff onto new helper xdp_convert_skb_to_buff() and embed there rxq's mem_type initialization that is assigned to xdp_buff. Make it agnostic to current skb->data position. This problem was triggered by syzbot as well as AF_XDP test suite which is about to be integrated to BPF CI. Reported-by: [email protected] Closes: https://lore.kernel.org/netdev/[email protected]/ Fixes: e6d5dbd ("xdp: add multi-buff support for xdp running in generic mode") Tested-by: Ihor Solodrai <[email protected]> Reviewed-by: Toke Høiland-Jørgensen <[email protected]> Co-developed-by: Octavian Purdila <[email protected]> Signed-off-by: Octavian Purdila <[email protected]> # whole analysis, testing, initiating a fix Signed-off-by: Maciej Fijalkowski <[email protected]> # commit msg and proposed more robust fix
When skb's headroom is not sufficient for XDP purposes,
skb_pp_cow_data() returns new skb with requested headroom space. This
skb was provided by page_pool.
For CONFIG_DEBUG_VM=y and XDP program that uses bpf_xdp_adjust_tail()
against a skb with frags, and mentioned helper consumed enough amount of
bytes that in turn released the page, following splat was observed:
[ 32.204881] BUG: Bad page state in process test_progs pfn:11c98b
[ 32.207167] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x11c98b
[ 32.210084] flags: 0x1fffe0000000000(node=0|zone=1|lastcpupid=0x7fff)
[ 32.212493] raw: 01fffe0000000000 dead000000000040 ff11000123c9b000 0000000000000000
[ 32.218056] raw: 0000000000000000 0000000000000001 00000000ffffffff 0000000000000000
[ 32.220900] page dumped because: page_pool leak
[ 32.222636] Modules linked in: bpf_testmod(O) bpf_preload
[ 32.224632] CPU: 6 UID: 0 PID: 3612 Comm: test_progs Tainted: G O 6.17.0-rc5-gfec474d29325 #6969 PREEMPT
[ 32.224638] Tainted: [O]=OOT_MODULE
[ 32.224639] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[ 32.224641] Call Trace:
[ 32.224644] <IRQ>
[ 32.224646] dump_stack_lvl+0x4b/0x70
[ 32.224653] bad_page.cold+0xbd/0xe0
[ 32.224657] __free_frozen_pages+0x838/0x10b0
[ 32.224660] ? skb_pp_cow_data+0x782/0xc30
[ 32.224665] bpf_xdp_shrink_data+0x221/0x530
[ 32.224668] ? skb_pp_cow_data+0x6d1/0xc30
[ 32.224671] bpf_xdp_adjust_tail+0x598/0x810
[ 32.224673] ? xsk_destruct_skb+0x321/0x800
[ 32.224678] bpf_prog_004ac6bb21de57a7_xsk_xdp_adjust_tail+0x52/0xd6
[ 32.224681] veth_xdp_rcv_skb+0x45d/0x15a0
[ 32.224684] ? get_stack_info_noinstr+0x16/0xe0
[ 32.224688] ? veth_set_channels+0x920/0x920
[ 32.224691] ? get_stack_info+0x2f/0x80
[ 32.224693] ? unwind_next_frame+0x3af/0x1df0
[ 32.224697] veth_xdp_rcv.constprop.0+0x38a/0xbe0
[ 32.224700] ? common_startup_64+0x13e/0x148
[ 32.224703] ? veth_xdp_rcv_one+0xcd0/0xcd0
[ 32.224706] ? stack_trace_save+0x84/0xa0
[ 32.224709] ? stack_depot_save_flags+0x28/0x820
[ 32.224713] ? __resched_curr.constprop.0+0x332/0x3b0
[ 32.224716] ? timerqueue_add+0x217/0x320
[ 32.224719] veth_poll+0x115/0x5e0
[ 32.224722] ? veth_xdp_rcv.constprop.0+0xbe0/0xbe0
[ 32.224726] ? update_load_avg+0x1cb/0x12d0
[ 32.224730] ? update_cfs_group+0x121/0x2c0
[ 32.224733] __napi_poll+0xa0/0x420
[ 32.224736] net_rx_action+0x901/0xe90
[ 32.224740] ? run_backlog_napi+0x50/0x50
[ 32.224743] ? clockevents_program_event+0x1cc/0x280
[ 32.224746] ? hrtimer_interrupt+0x31e/0x7c0
[ 32.224749] handle_softirqs+0x151/0x430
[ 32.224752] do_softirq+0x3f/0x60
[ 32.224755] </IRQ>
It's because xdp_rxq with mem model set to MEM_TYPE_PAGE_SHARED was used
when initializing xdp_buff.
Fix this by using new helper xdp_convert_skb_to_buff() that, besides
init/prepare xdp_buff, will check if page used for linear part of
xdp_buff comes from page_pool. We assume that linear data and frags will
have same memory provider as currently XDP API does not provide us a way
to distinguish it (the mem model is registered for *whole* Rx queue and
here we speak about single buffer granularity).
Before releasing xdp_buff out of veth via XDP_{TX,REDIRECT}, mem type on
xdp_rxq associated with xdp_buff is restored to its original model. We
need to respect previous setting at least until buff is converted to
frame, as frame carries the mem_type. Add a page_pool variant of
veth_xdp_get() so that we avoid refcount underflow when draining page
frag.
Fixes: 0ebab78 ("net: veth: add page_pool for page recycling")
Reported-by: Alexei Starovoitov <[email protected]>
Closes: https://lore.kernel.org/bpf/CAADnVQ+bBofJDfieyOYzSmSujSfJwDTQhiz3aJw7hE+4E2_iPA@mail.gmail.com/
Signed-off-by: Maciej Fijalkowski <[email protected]>
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At least one diff in series https://patchwork.kernel.org/project/netdevbpf/list/?series=1014515 expired. Closing PR. |
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Pull request for series with
subject: xdp: fix page_pool leaks
version: 3
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1014515