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Date: Mon, 06 Nov 2023 13:44:02 +0100
From: Jakub Sitnicki <jakub@...udflare.com>
To: John Fastabend <john.fastabend@...il.com>
Cc: bpf@...r.kernel.org, netdev@...r.kernel.org, yangyingliang@...wei.com,
martin.lau@...nel.org
Subject: Re: [PATCH bpf 2/2] bpf: sockmap, add af_unix test with both
sockets in map
On Mon, Oct 16, 2023 at 12:08 PM -07, John Fastabend wrote:
> This adds a test where both pairs of a af_unix paired socket are put into
> a BPF map. This ensures that when we tear down the af_unix pair we don't
> have any issues on sockmap side with ordering and reference counting.
>
> Signed-off-by: John Fastabend <john.fastabend@...il.com>
> ---
> .../selftests/bpf/prog_tests/sockmap_listen.c | 39 ++++++++++++++++---
> .../selftests/bpf/progs/test_sockmap_listen.c | 7 ++++
> 2 files changed, 40 insertions(+), 6 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/sockmap_listen.c b/tools/testing/selftests/bpf/prog_tests/sockmap_listen.c
> index 8df8cbb447f1..90e97907c1c1 100644
> --- a/tools/testing/selftests/bpf/prog_tests/sockmap_listen.c
> +++ b/tools/testing/selftests/bpf/prog_tests/sockmap_listen.c
> @@ -1824,8 +1824,10 @@ static void inet_unix_skb_redir_to_connected(struct test_sockmap_listen *skel,
> xbpf_prog_detach2(verdict, sock_map, BPF_SK_SKB_VERDICT);
> }
>
> -static void unix_inet_redir_to_connected(int family, int type, int sock_mapfd,
> - int verd_mapfd, enum redir_mode mode)
> +static void unix_inet_redir_to_connected(int family, int type,
> + int sock_mapfd, int nop_mapfd,
> + int verd_mapfd,
> + enum redir_mode mode)
> {
> const char *log_prefix = redir_mode_str(mode);
> int c0, c1, p0, p1;
> @@ -1849,6 +1851,12 @@ static void unix_inet_redir_to_connected(int family, int type, int sock_mapfd,
> if (err)
> goto close;
>
> + if (nop_mapfd >= 0) {
> + err = add_to_sockmap(nop_mapfd, c0, c1);
> + if (err)
> + goto close;
> + }
> +
> n = write(c1, "a", 1);
> if (n < 0)
> FAIL_ERRNO("%s: write", log_prefix);
> @@ -1883,6 +1891,7 @@ static void unix_inet_skb_redir_to_connected(struct test_sockmap_listen *skel,
> struct bpf_map *inner_map, int family)
> {
> int verdict = bpf_program__fd(skel->progs.prog_skb_verdict);
> + int nop_map = bpf_map__fd(skel->maps.nop_map);
> int verdict_map = bpf_map__fd(skel->maps.verdict_map);
> int sock_map = bpf_map__fd(inner_map);
> int err;
> @@ -1892,14 +1901,32 @@ static void unix_inet_skb_redir_to_connected(struct test_sockmap_listen *skel,
> return;
>
> skel->bss->test_ingress = false;
> - unix_inet_redir_to_connected(family, SOCK_DGRAM, sock_map, verdict_map,
> + unix_inet_redir_to_connected(family, SOCK_DGRAM,
> + sock_map, -1, verdict_map,
> + REDIR_EGRESS);
> + unix_inet_redir_to_connected(family, SOCK_DGRAM,
> + sock_map, -1, verdict_map,
> REDIR_EGRESS);
> - unix_inet_redir_to_connected(family, SOCK_STREAM, sock_map, verdict_map,
> +
> + unix_inet_redir_to_connected(family, SOCK_DGRAM,
> + sock_map, nop_map, verdict_map,
> + REDIR_EGRESS);
> + unix_inet_redir_to_connected(family, SOCK_STREAM,
> + sock_map, nop_map, verdict_map,
> REDIR_EGRESS);
> skel->bss->test_ingress = true;
> - unix_inet_redir_to_connected(family, SOCK_DGRAM, sock_map, verdict_map,
> + unix_inet_redir_to_connected(family, SOCK_DGRAM,
> + sock_map, -1, verdict_map,
> + REDIR_INGRESS);
> + unix_inet_redir_to_connected(family, SOCK_STREAM,
> + sock_map, -1, verdict_map,
> + REDIR_INGRESS);
> +
> + unix_inet_redir_to_connected(family, SOCK_DGRAM,
> + sock_map, nop_map, verdict_map,
> REDIR_INGRESS);
> - unix_inet_redir_to_connected(family, SOCK_STREAM, sock_map, verdict_map,
> + unix_inet_redir_to_connected(family, SOCK_STREAM,
> + sock_map, nop_map, verdict_map,
> REDIR_INGRESS);
>
> xbpf_prog_detach2(verdict, sock_map, BPF_SK_SKB_VERDICT);
> diff --git a/tools/testing/selftests/bpf/progs/test_sockmap_listen.c b/tools/testing/selftests/bpf/progs/test_sockmap_listen.c
> index 464d35bd57c7..b7250eb9c30c 100644
> --- a/tools/testing/selftests/bpf/progs/test_sockmap_listen.c
> +++ b/tools/testing/selftests/bpf/progs/test_sockmap_listen.c
> @@ -14,6 +14,13 @@ struct {
> __type(value, __u64);
> } sock_map SEC(".maps");
>
> +struct {
> + __uint(type, BPF_MAP_TYPE_SOCKMAP);
> + __uint(max_entries, 2);
> + __type(key, __u32);
> + __type(value, __u64);
> +} nop_map SEC(".maps");
> +
> struct {
> __uint(type, BPF_MAP_TYPE_SOCKHASH);
> __uint(max_entries, 2);
So... we have a bug in unix_inet_redir_to_connected() - it happily
ignores the passed socket type, which is currently hardcoded to
SOCK_DGRAM :-)
Which means these tests don't exercise unix_stream paths where the added
psock->skpair is actually needed.
But I'm able to reproduce the bug by running the VSOCK redir test:
bash-5.2# ./test_progs -n 212/79
[ 23.232282] ==================================================================
[ 23.232634] BUG: KASAN: slab-use-after-free in sock_def_readable+0xe3/0x400
[ 23.232942] Read of size 8 at addr ffff8881013f9860 by task kworker/1:2/220
[ 23.233253]
[ 23.233326] CPU: 1 PID: 220 Comm: kworker/1:2 Tainted: G OE 6.6.0 #30
[ 23.233697] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-1.fc38 04/01/2014
[ 23.234074] Workqueue: events sk_psock_backlog
[ 23.234271] Call Trace:
[ 23.234381] <TASK>
[ 23.234477] dump_stack_lvl+0x4a/0x90
[ 23.234640] print_address_description.constprop.0+0x33/0x400
[ 23.234888] ? preempt_count_sub+0x13/0xc0
[ 23.235071] print_report+0xb6/0x260
[ 23.235228] ? kasan_complete_mode_report_info+0x7c/0x1f0
[ 23.235462] kasan_report+0xd0/0x110
[ 23.235619] ? sock_def_readable+0xe3/0x400
[ 23.235801] ? sock_def_readable+0xe3/0x400
[ 23.235989] kasan_check_range+0xf7/0x1b0
[ 23.236164] __kasan_check_read+0x11/0x20
[ 23.236340] sock_def_readable+0xe3/0x400
[ 23.236514] unix_stream_sendmsg+0x3c5/0x7d0
[ 23.236704] ? queue_oob+0x300/0x300
[ 23.236865] sock_sendmsg+0x229/0x250
[ 23.237030] ? sock_write_iter+0x320/0x320
[ 23.237211] ? __this_cpu_preempt_check+0x13/0x20
[ 23.237416] ? lock_acquire+0x191/0x410
[ 23.237607] ? lock_sync+0x110/0x110
[ 23.237766] ? lock_is_held_type+0xd0/0x130
[ 23.237948] ? __asan_storeN+0x12/0x20
[ 23.238115] __skb_send_sock+0x4fa/0x670
[ 23.238288] ? preempt_count_sub+0x13/0xc0
[ 23.238494] ? sendmsg_locked+0x90/0x90
[ 23.238721] ? sendmsg_unlocked+0x40/0x40
[ 23.238975] ? __lock_acquire+0x765/0xf00
[ 23.239252] ? __this_cpu_preempt_check+0x13/0x20
[ 23.239570] ? lock_acquire+0x191/0x410
[ 23.239831] skb_send_sock+0x10/0x20
[ 23.240079] sk_psock_backlog+0x141/0x5e0
[ 23.240340] ? __this_cpu_preempt_check+0x13/0x20
[ 23.240638] process_one_work+0x49d/0x970
[ 23.240900] ? drain_workqueue+0x1c0/0x1c0
[ 23.241173] ? assign_work+0xe1/0x120
[ 23.241404] worker_thread+0x380/0x680
[ 23.241660] ? trace_hardirqs_on+0x22/0x100
[ 23.241933] ? preempt_count_sub+0x13/0xc0
[ 23.242213] ? process_one_work+0x970/0x970
[ 23.242491] kthread+0x1ba/0x200
[ 23.242687] ? kthread+0xfe/0x200
[ 23.242890] ? kthread_complete_and_exit+0x20/0x20
[ 23.243193] ret_from_fork+0x35/0x60
[ 23.243418] ? kthread_complete_and_exit+0x20/0x20
[ 23.243718] ret_from_fork_asm+0x11/0x20
[ 23.243995] </TASK>
[ 23.244145]
[ 23.244227] Allocated by task 227:
[ 23.244446] kasan_save_stack+0x26/0x50
[ 23.244709] kasan_set_track+0x25/0x40
[ 23.244951] kasan_save_alloc_info+0x1e/0x30
[ 23.245220] __kasan_slab_alloc+0x72/0x80
[ 23.245491] kmem_cache_alloc+0x182/0x360
[ 23.245758] sk_prot_alloc+0x43/0x160
[ 23.246007] sk_alloc+0x2c/0x3a0
[ 23.246216] unix_create1+0x86/0x440
[ 23.246462] unix_create+0x7d/0x100
[ 23.246701] __sock_create+0x1bc/0x420
[ 23.246960] __sys_socketpair+0x1ac/0x3a0
[ 23.247237] __x64_sys_socketpair+0x4f/0x60
[ 23.247521] do_syscall_64+0x38/0x90
[ 23.247769] entry_SYSCALL_64_after_hwframe+0x63/0xcd
[ 23.248113]
[ 23.248225] Freed by task 227:
[ 23.248444] kasan_save_stack+0x26/0x50
[ 23.248707] kasan_set_track+0x25/0x40
[ 23.248963] kasan_save_free_info+0x2b/0x50
[ 23.249249] ____kasan_slab_free+0x154/0x1c0
[ 23.249541] __kasan_slab_free+0x12/0x20
[ 23.249810] kmem_cache_free+0x1e7/0x480
[ 23.250084] __sk_destruct+0x270/0x3f0
[ 23.250342] sk_destruct+0x78/0x90
[ 23.250577] __sk_free+0x51/0x160
[ 23.250807] sk_free+0x45/0x70
[ 23.251025] unix_release_sock+0x5cc/0x700
[ 23.251301] unix_release+0x50/0x70
[ 23.251536] __sock_release+0x5f/0x120
[ 23.251754] sock_close+0x13/0x20
[ 23.252109] __fput+0x1f3/0x470
[ 23.252451] __fput_sync+0x2f/0x40
[ 23.252811] __x64_sys_close+0x51/0x90
[ 23.253169] do_syscall_64+0x38/0x90
[ 23.253480] entry_SYSCALL_64_after_hwframe+0x63/0xcd
[ 23.253940]
[ 23.254097] The buggy address belongs to the object at ffff8881013f9800
[ 23.254097] which belongs to the cache UNIX-STREAM of size 1920
[ 23.254936] The buggy address is located 96 bytes inside of
[ 23.254936] freed 1920-byte region [ffff8881013f9800, ffff8881013f9f80)
[ 23.255731]
[ 23.255844] The buggy address belongs to the physical page:
[ 23.256225] page:00000000c005ecb3 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff8881013f8000 pfn:0x1013f8
[ 23.256905] head:00000000c005ecb3 order:3 entire_mapcount:0 nr_pages_mapped:0 pincount:0
[ 23.257382] flags: 0x2fffe000000840(slab|head|node=0|zone=2|lastcpupid=0x7fff)
[ 23.257791] page_type: 0xffffffff()
[ 23.257988] raw: 002fffe000000840 ffff888100961a40 dead000000000122 0000000000000000
[ 23.258418] raw: ffff8881013f8000 000000008010000e 00000001ffffffff 0000000000000000
[ 23.258817] page dumped because: kasan: bad access detected
[ 23.259131]
[ 23.259205] Memory state around the buggy address:
[ 23.259469] ffff8881013f9700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 23.259871] ffff8881013f9780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 23.260290] >ffff8881013f9800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 23.260704] ^
[ 23.261056] ffff8881013f9880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 23.261469] ffff8881013f9900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 23.261854] ==================================================================
[ 23.262453] Disabling lock debugging due to kernel taint
#212/79 sockmap_listen/sockmap VSOCK test_vsock_redir:OK
#212 sockmap_listen:OK
Summary: 1/1 PASSED, 0 SKIPPED, 0 FAILED
bash-5.2#
If I modify the test to use (AF_UNIX, SOCK_DGRAM) instead of
SOCK_STREAM, the bug no longer reproduces.
Which confirms my thinking that unix_dgram_sendmsg is safe to use from
sockmap because it grabs a ref to skpair.
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