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Hello,
On Wed, 2 Oct 2019, Davide Caratti wrote:
> if the IPVS module is removed while the sync daemon is starting, there is
> a small possibility for stop_sync_thread() to end successfully just after
> start_sync_thread() released sync_mutex, but before increasing the module
> refcount. When this race happens, the following warning is seen in dmesg:
>
> IPVS: stopping master sync thread 14134 ...
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 14133 at kernel/module.c:1137
> module_put.part.44+0x167/0x2a0
> Modules linked in: ip_vs(-) nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4
> sch_netem veth ip6table_filter ip6_tables iptable_filter binfmt_misc
> intel_rapl_msr intel_rapl_common crct10dif_pclmul crc32_pclmul
> ghash_clmulni_intel snd_hda_codec_generic ledtrig_audio snd_hda_intel
> snd_hda_codec ext4 snd_hda_core snd_hwdep mbcache jbd2 snd_seq snd_seq_device
> snd_pcm aesni_intel crypto_simd cryptd glue_helper joydev snd_timer
> virtio_balloon pcspkr snd soundcore i2c_piix4 nfsd auth_rpcgss nfs_acl lockd
> grace sunrpc ip_tables xfs libcrc32c ata_generic pata_acpi virtio_net
> virtio_console virtio_blk net_failover failover qxl drm_kms_helper
> syscopyarea sysfillrect sysimgblt fb_sys_fops ttm crc32c_intel serio_raw
> ata_piix virtio_pci drm virtio_ring virtio libata floppy dm_mirror
> dm_region_hash dm_log dm_mod [last unloaded: nf_defrag_ipv6]
> CPU: 0 PID: 14133 Comm: modprobe Tainted: G W
> 5.3.0-rc7.upstream+ #723
> Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
> RIP: 0010:module_put.part.44+0x167/0x2a0
> Code: 48 83 c4 68 5b 5d 41 5c 41 5d 41 5e 41 5f c3 89 44 24 28 83 e8 01 89
> c5 0f 89 57 ff ff ff 48 c7 c7 60 9c ed 86 e8 32 4c f5 ff <0f> 0b e9 6c ff ff
> ff 65 8b 1d 6b b2 e6 7a 89 db be 08 00 00 00 48
> RSP: 0018:ffff88804f9b7c78 EFLAGS: 00010282
> RAX: 0000000000000024 RBX: ffffffffc1609690 RCX: ffffffff85a82042
> RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffff888053627bec
> RBP: 00000000ffffffff R08: ffffed100a6c6181 R09: ffffed100a6c6181
> R10: 0000000000000001 R11: ffffed100a6c6180 R12: 1ffff11009f36f90
> R13: ffffffffc1609300 R14: ffff88804c0d5500 R15: ffff88804c0d5ea0
> FS: 00007fa1c73f8740(0000) GS:ffff888053600000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f914f4d345f CR3: 000000004855a005 CR4: 00000000001606f0
> Call Trace:
> stop_sync_thread+0x3a3/0x7c0 [ip_vs]
> ip_vs_sync_net_cleanup+0x13/0x50 [ip_vs]
> ops_exit_list.isra.5+0x94/0x140
> unregister_pernet_operations+0x29d/0x460
> unregister_pernet_device+0x26/0x60
> ip_vs_cleanup+0x11/0x38 [ip_vs]
> do_syscall_64+0xa5/0x4f0
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x7fa1c68c9027
> Code: 73 01 c3 48 8b 0d 69 6e 2c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f
> 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 b0 00 00 00 0f 05 <48> 3d 01 f0 ff ff
> 73 01 c3 48 8b 0d 39 6e 2c 00 f7 d8 64 89 01 48
> RSP: 002b:00007ffe8b021cf8 EFLAGS: 00000202 ORIG_RAX: 00000000000000b0
> RAX: ffffffffffffffda RBX: 0000000001528240 RCX: 00007fa1c68c9027
> RDX: 0000000000000000 RSI: 0000000000000800 RDI: 00000000015282a8
> RBP: 0000000000000000 R08: 00007fa1c6b91060 R09: 00007fa1c693d1a0
> R10: 00007ffe8b021760 R11: 0000000000000202 R12: 0000000000000000
> R13: 0000000000000001 R14: 00000000015282a8 R15: 0000000000000000
>
> Fix this ensuring that start_sync_thread() takes a refcount for the ip_vs
> module earlier, and eventually drop it in the error path.
>
> Reported-by: Zhi Li <yieli@xxxxxxxxxx>
> Signed-off-by: Davide Caratti <dcaratti@xxxxxxxxxx>
> ---
> net/netfilter/ipvs/ip_vs_sync.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/net/netfilter/ipvs/ip_vs_sync.c b/net/netfilter/ipvs/ip_vs_sync.c
> index a4a78c4b06de..7ac148182b61 100644
> --- a/net/netfilter/ipvs/ip_vs_sync.c
> +++ b/net/netfilter/ipvs/ip_vs_sync.c
> @@ -1758,6 +1758,9 @@ int start_sync_thread(struct netns_ipvs *ipvs, struct
> ipvs_sync_daemon_cfg *c,
> int result = -ENOMEM;
> u16 mtu, min_mtu;
>
> + /* increase the module use count */
> + ip_vs_use_count_inc();
> +
May be this is not early enough. When control hooks
are the first thing to disconnect with ip_vs_unregister_nl_ioctl()
how start_sync_thread() is called concurrently? ip_vs_sockopts is
protected with .owner field and ip_vs_genl_family with .module field
or more correctly with cb_lock rwsem in net/netlink/genetlink.c
which avoids doit() handlers after genl_unregister_family() is called.
So, both interfaces do not allow start_sync_thread() during module
removal and it is interesting how your fix works actually.
Which interface calls start_sync_thread (sockopt/genl)? Note that
do_ip_vs_set_ctl() already has ip_vs_use_count_inc() before the
start_sync_thread() call. Also, the WARN in module_put warns
about refcnt underflow, so there is an extra ip_vs_use_count_dec() ?
Another possibility is the missing checks for
ip_vs_use_count_inc() result to cause underflow on ip_vs_use_count_dec().
Are there any steps to reproduce?
> IP_VS_DBG(7, "%s(): pid %d\n", __func__, task_pid_nr(current));
> IP_VS_DBG(7, "Each ip_vs_sync_conn entry needs %zd bytes\n",
> sizeof(struct ip_vs_sync_conn_v0));
> @@ -1892,9 +1895,6 @@ int start_sync_thread(struct netns_ipvs *ipvs, struct
> ipvs_sync_daemon_cfg *c,
> mutex_unlock(&ipvs->sync_mutex);
> rtnl_unlock();
>
> - /* increase the module use count */
> - ip_vs_use_count_inc();
> -
> return 0;
>
> out:
> @@ -1924,11 +1924,16 @@ int start_sync_thread(struct netns_ipvs *ipvs, struct
> ipvs_sync_daemon_cfg *c,
> }
> kfree(ti);
> }
> +
> + /* decrease the module use count */
> + ip_vs_use_count_dec();
> return result;
>
> out_early:
> mutex_unlock(&ipvs->sync_mutex);
> rtnl_unlock();
> + /* decrease the module use count */
> + ip_vs_use_count_dec();
> return result;
> }
>
> --
> 2.21.0
Regards
--
Julian Anastasov <ja@xxxxxx>
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