Question regarding sysctl network parameters #55

Utini2000 · 2020-12-30T16:48:32Z

Hello everyone,
today I read this guide and double checked its recommendations with the parameters from linux-hardened:
https://madaidans-insecurities.github.io/guides/linux-hardening.html#sysctl-network

I noticed that some of the network parameters in linux-hardened are not as strict/secure as recommended in the guide.
Is this on purpose or are those values that might need some tuning in the future?

Just wanted to give a hint to it in case it has been "overseen" :-)

Thanks!

five23 · 2021-07-18T03:24:08Z

Some notes on the discrepancies:

net.ipv4.tcp_sack=0

Disabling this can cause TCP congestion on higher latency connections such as WiFi. Instead try blocking connections with a low MSS using iptables => iptables -A INPUT -p tcp -m tcpmss --mss 1:500 -j DROP (https://www.suse.com/support/kb/doc/?id=000019472).

net.ipv4.tcp_dsack=0

Hmm, not sure about this one. DSACK informs the sender of duplicate arrivals so I don't think disabling it would make any difference to a malicious sender?

net.ipv4.tcp_fack=0

This option is deprecated and has no effect (see: https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt)

net.ipv4.icmp_echo_ignore_all=1

Generally it's better to respond to ping requests and instead configure your router to ignore packets where the source address is a broadcast address, et. al. The defaults here make sense to me.

[ Upstream commit 059a47f ] After rx/tx ring buffer size is changed, kernel panic occurs when it acts XDP_TX or XDP_REDIRECT. When tx/rx ring buffer size is changed(ethtool -G), sfc driver reallocates and reinitializes rx and tx queues and their buffer (tx_queue->buffer). But it misses reinitializing xdp queues(efx->xdp_tx_queues). So, while it is acting XDP_TX or XDP_REDIRECT, it uses the uninitialized tx_queue->buffer. A new function efx_set_xdp_channels() is separated from efx_set_channels() to handle only xdp queues. Splat looks like: BUG: kernel NULL pointer dereference, address: 000000000000002a #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: 0002 [#4] PREEMPT SMP NOPTI RIP: 0010:efx_tx_map_chunk+0x54/0x90 [sfc] CPU: 2 PID: 0 Comm: swapper/2 Tainted: G D 5.17.0+ #55 e8beeee8289528f11357029357cf Code: 48 8b 8d a8 01 00 00 48 8d 14 52 4c 8d 2c d0 44 89 e0 48 85 c9 74 0e 44 89 e2 4c 89 f6 48 80 RSP: 0018:ffff92f121e45c60 EFLAGS: 00010297 RIP: 0010:efx_tx_map_chunk+0x54/0x90 [sfc] RAX: 0000000000000040 RBX: ffff92ea506895c0 RCX: ffffffffc0330870 RDX: 0000000000000001 RSI: 00000001139b10ce RDI: ffff92ea506895c0 RBP: ffffffffc0358a80 R08: 00000001139b110d R09: 0000000000000000 R10: 0000000000000001 R11: ffff92ea414c0088 R12: 0000000000000040 R13: 0000000000000018 R14: 00000001139b10ce R15: ffff92ea506895c0 FS: 0000000000000000(0000) GS:ffff92f121ec0000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 Code: 48 8b 8d a8 01 00 00 48 8d 14 52 4c 8d 2c d0 44 89 e0 48 85 c9 74 0e 44 89 e2 4c 89 f6 48 80 CR2: 000000000000002a CR3: 00000003e6810004 CR4: 00000000007706e0 RSP: 0018:ffff92f121e85c60 EFLAGS: 00010297 PKRU: 55555554 RAX: 0000000000000040 RBX: ffff92ea50689700 RCX: ffffffffc0330870 RDX: 0000000000000001 RSI: 00000001145a90ce RDI: ffff92ea50689700 RBP: ffffffffc0358a80 R08: 00000001145a910d R09: 0000000000000000 R10: 0000000000000001 R11: ffff92ea414c0088 R12: 0000000000000040 R13: 0000000000000018 R14: 00000001145a90ce R15: ffff92ea50689700 FS: 0000000000000000(0000) GS:ffff92f121e80000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000000000002a CR3: 00000003e6810005 CR4: 00000000007706e0 PKRU: 55555554 Call Trace: <IRQ> efx_xdp_tx_buffers+0x12b/0x3d0 [sfc 84c94b8e32d44d296c17e10a634d3ad454de4ba5] __efx_rx_packet+0x5c3/0x930 [sfc 84c94b8e32d44d296c17e10a634d3ad454de4ba5] efx_rx_packet+0x28c/0x2e0 [sfc 84c94b8e32d44d296c17e10a634d3ad454de4ba5] efx_ef10_ev_process+0x5f8/0xf40 [sfc 84c94b8e32d44d296c17e10a634d3ad454de4ba5] ? enqueue_task_fair+0x95/0x550 efx_poll+0xc4/0x360 [sfc 84c94b8e32d44d296c17e10a634d3ad454de4ba5] Fixes: 3990a8f ("sfc: allocate channels for XDP tx queues") Signed-off-by: Taehee Yoo <[email protected]> Signed-off-by: David S. Miller <[email protected]> Signed-off-by: Sasha Levin <[email protected]>

[ Upstream commit d28ea55 ] Add calls to drm_bridge_add()/drm_bridge_remove() DRM bridges created by the driver. This fixes the following warning. WARNING: CPU: 0 PID: 1 at kernel/locking/mutex.c:579 __mutex_lock+0x840/0x9f4 DEBUG_LOCKS_WARN_ON(lock->magic != lock) Modules linked in: CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.18.0-rc1-00002-g3054695a0d27-dirty #55 Hardware name: Generic DT based system unwind_backtrace from show_stack+0x10/0x14 show_stack from dump_stack_lvl+0x58/0x70 dump_stack_lvl from __warn+0xc8/0x1e8 __warn from warn_slowpath_fmt+0x78/0xa8 warn_slowpath_fmt from __mutex_lock+0x840/0x9f4 __mutex_lock from mutex_lock_nested+0x1c/0x24 mutex_lock_nested from drm_bridge_hpd_enable+0x2c/0x84 drm_bridge_hpd_enable from msm_hdmi_modeset_init+0xc0/0x21c msm_hdmi_modeset_init from mdp4_kms_init+0x53c/0x90c mdp4_kms_init from msm_drm_bind+0x514/0x698 msm_drm_bind from try_to_bring_up_aggregate_device+0x160/0x1bc try_to_bring_up_aggregate_device from component_master_add_with_match+0xc4/0xf8 component_master_add_with_match from msm_pdev_probe+0x274/0x350 msm_pdev_probe from platform_probe+0x5c/0xbc platform_probe from really_probe.part.0+0x9c/0x290 really_probe.part.0 from __driver_probe_device+0xa8/0x13c __driver_probe_device from driver_probe_device+0x34/0x10c driver_probe_device from __driver_attach+0xbc/0x178 __driver_attach from bus_for_each_dev+0x74/0xc0 bus_for_each_dev from bus_add_driver+0x160/0x1e4 bus_add_driver from driver_register+0x88/0x118 driver_register from do_one_initcall+0x6c/0x334 do_one_initcall from kernel_init_freeable+0x1bc/0x220 kernel_init_freeable from kernel_init+0x18/0x12c kernel_init from ret_from_fork+0x14/0x2c Fixes: 3d3f8b1 ("drm/bridge: make bridge registration independent of drm flow") Reported-by: kernel test robot <[email protected]> Signed-off-by: Dmitry Baryshkov <[email protected]> Reviewed-by: Stephen Boyd <[email protected]> Reviewed-by: Abhinav Kumar <[email protected]> Patchwork: https://patchwork.freedesktop.org/patch/481778/ Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Dmitry Baryshkov <[email protected]> Signed-off-by: Sasha Levin <[email protected]>

[ Upstream commit dbc153f ] A crash was found when dumping SMC-D connections. It can be reproduced by following steps: - run nginx/wrk test: smc_run nginx smc_run wrk -t 16 -c 1000 -d <duration> -H 'Connection: Close' <URL> - continuously dump SMC-D connections in parallel: watch -n 1 'smcss -D' BUG: kernel NULL pointer dereference, address: 0000000000000030 CPU: 2 PID: 7204 Comm: smcss Kdump: loaded Tainted: G E 6.7.0+ #55 RIP: 0010:__smc_diag_dump.constprop.0+0x5e5/0x620 [smc_diag] Call Trace: <TASK> ? __die+0x24/0x70 ? page_fault_oops+0x66/0x150 ? exc_page_fault+0x69/0x140 ? asm_exc_page_fault+0x26/0x30 ? __smc_diag_dump.constprop.0+0x5e5/0x620 [smc_diag] ? __kmalloc_node_track_caller+0x35d/0x430 ? __alloc_skb+0x77/0x170 smc_diag_dump_proto+0xd0/0xf0 [smc_diag] smc_diag_dump+0x26/0x60 [smc_diag] netlink_dump+0x19f/0x320 __netlink_dump_start+0x1dc/0x300 smc_diag_handler_dump+0x6a/0x80 [smc_diag] ? __pfx_smc_diag_dump+0x10/0x10 [smc_diag] sock_diag_rcv_msg+0x121/0x140 ? __pfx_sock_diag_rcv_msg+0x10/0x10 netlink_rcv_skb+0x5a/0x110 sock_diag_rcv+0x28/0x40 netlink_unicast+0x22a/0x330 netlink_sendmsg+0x1f8/0x420 __sock_sendmsg+0xb0/0xc0 ____sys_sendmsg+0x24e/0x300 ? copy_msghdr_from_user+0x62/0x80 ___sys_sendmsg+0x7c/0xd0 ? __do_fault+0x34/0x160 ? do_read_fault+0x5f/0x100 ? do_fault+0xb0/0x110 ? __handle_mm_fault+0x2b0/0x6c0 __sys_sendmsg+0x4d/0x80 do_syscall_64+0x69/0x180 entry_SYSCALL_64_after_hwframe+0x6e/0x76 It is possible that the connection is in process of being established when we dump it. Assumed that the connection has been registered in a link group by smc_conn_create() but the rmb_desc has not yet been initialized by smc_buf_create(), thus causing the illegal access to conn->rmb_desc. So fix it by checking before dump. Fixes: 4b1b7d3 ("net/smc: add SMC-D diag support") Signed-off-by: Wen Gu <[email protected]> Reviewed-by: Dust Li <[email protected]> Reviewed-by: Wenjia Zhang <[email protected]> Signed-off-by: David S. Miller <[email protected]> Signed-off-by: Sasha Levin <[email protected]>

…_bind returns err [ Upstream commit 36684e9 ] The pointer need to be set to NULL, otherwise KASAN complains about use-after-free. Because in mtk_drm_bind, all private's drm are set as follows. private->all_drm_private[i]->drm = drm; And drm will be released by drm_dev_put in case mtk_drm_kms_init returns failure. However, the shutdown path still accesses the previous allocated memory in drm_atomic_helper_shutdown. [ 84.874820] watchdog: watchdog0: watchdog did not stop! [ 86.512054] ================================================================== [ 86.513162] BUG: KASAN: use-after-free in drm_atomic_helper_shutdown+0x33c/0x378 [ 86.514258] Read of size 8 at addr ffff0000d46fc068 by task shutdown/1 [ 86.515213] [ 86.515455] CPU: 1 UID: 0 PID: 1 Comm: shutdown Not tainted 6.13.0-rc1-mtk+gfa1a78e5d24b-dirty #55 [ 86.516752] Hardware name: Unknown Product/Unknown Product, BIOS 2022.10 10/01/2022 [ 86.517960] Call trace: [ 86.518333] show_stack+0x20/0x38 (C) [ 86.518891] dump_stack_lvl+0x90/0xd0 [ 86.519443] print_report+0xf8/0x5b0 [ 86.519985] kasan_report+0xb4/0x100 [ 86.520526] __asan_report_load8_noabort+0x20/0x30 [ 86.521240] drm_atomic_helper_shutdown+0x33c/0x378 [ 86.521966] mtk_drm_shutdown+0x54/0x80 [ 86.522546] platform_shutdown+0x64/0x90 [ 86.523137] device_shutdown+0x260/0x5b8 [ 86.523728] kernel_restart+0x78/0xf0 [ 86.524282] __do_sys_reboot+0x258/0x2f0 [ 86.524871] __arm64_sys_reboot+0x90/0xd8 [ 86.525473] invoke_syscall+0x74/0x268 [ 86.526041] el0_svc_common.constprop.0+0xb0/0x240 [ 86.526751] do_el0_svc+0x4c/0x70 [ 86.527251] el0_svc+0x4c/0xc0 [ 86.527719] el0t_64_sync_handler+0x144/0x168 [ 86.528367] el0t_64_sync+0x198/0x1a0 [ 86.528920] [ 86.529157] The buggy address belongs to the physical page: [ 86.529972] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff0000d46fd4d0 pfn:0x1146fc [ 86.531319] flags: 0xbfffc0000000000(node=0|zone=2|lastcpupid=0xffff) [ 86.532267] raw: 0bfffc0000000000 0000000000000000 dead000000000122 0000000000000000 [ 86.533390] raw: ffff0000d46fd4d0 0000000000000000 00000000ffffffff 0000000000000000 [ 86.534511] page dumped because: kasan: bad access detected [ 86.535323] [ 86.535559] Memory state around the buggy address: [ 86.536265] ffff0000d46fbf00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff [ 86.537314] ffff0000d46fbf80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff [ 86.538363] >ffff0000d46fc000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff [ 86.544733] ^ [ 86.551057] ffff0000d46fc080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff [ 86.557510] ffff0000d46fc100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff [ 86.563928] ================================================================== [ 86.571093] Disabling lock debugging due to kernel taint [ 86.577642] Unable to handle kernel paging request at virtual address e0e9c0920000000b [ 86.581834] KASAN: maybe wild-memory-access in range [0x0752049000000058-0x075204900000005f] ... Fixes: 1ef7ed4 ("drm/mediatek: Modify mediatek-drm for mt8195 multi mmsys support") Signed-off-by: Guoqing Jiang <[email protected]> Reviewed-by: AngeloGioacchino Del Regno <[email protected]> Link: https://patchwork.kernel.org/project/dri-devel/patch/[email protected]/ Signed-off-by: Chun-Kuang Hu <[email protected]> Signed-off-by: Sasha Levin <[email protected]>

commit b150654 upstream. Commit <d74169ceb0d2> ("iommu/vt-d: Allocate DMAR fault interrupts locally") moved the call to enable_drhd_fault_handling() to a code path that does not hold any lock while traversing the drhd list. Fix it by ensuring the dmar_global_lock lock is held when traversing the drhd list. Without this fix, the following warning is triggered: ============================= WARNING: suspicious RCU usage 6.14.0-rc3 #55 Not tainted ----------------------------- drivers/iommu/intel/dmar.c:2046 RCU-list traversed in non-reader section!! other info that might help us debug this: rcu_scheduler_active = 1, debug_locks = 1 2 locks held by cpuhp/1/23: #0: ffffffff84a67c50 (cpu_hotplug_lock){++++}-{0:0}, at: cpuhp_thread_fun+0x87/0x2c0 #1: ffffffff84a6a380 (cpuhp_state-up){+.+.}-{0:0}, at: cpuhp_thread_fun+0x87/0x2c0 stack backtrace: CPU: 1 UID: 0 PID: 23 Comm: cpuhp/1 Not tainted 6.14.0-rc3 #55 Call Trace: <TASK> dump_stack_lvl+0xb7/0xd0 lockdep_rcu_suspicious+0x159/0x1f0 ? __pfx_enable_drhd_fault_handling+0x10/0x10 enable_drhd_fault_handling+0x151/0x180 cpuhp_invoke_callback+0x1df/0x990 cpuhp_thread_fun+0x1ea/0x2c0 smpboot_thread_fn+0x1f5/0x2e0 ? __pfx_smpboot_thread_fn+0x10/0x10 kthread+0x12a/0x2d0 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x4a/0x60 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 </TASK> Holding the lock in enable_drhd_fault_handling() triggers a lockdep splat about a possible deadlock between dmar_global_lock and cpu_hotplug_lock. This is avoided by not holding dmar_global_lock when calling iommu_device_register(), which initiates the device probe process. Fixes: d74169c ("iommu/vt-d: Allocate DMAR fault interrupts locally") Reported-and-tested-by: Ido Schimmel <[email protected]> Closes: https://lore.kernel.org/linux-iommu/[email protected]/ Tested-by: Breno Leitao <[email protected]> Cc: [email protected] Signed-off-by: Lu Baolu <[email protected]> Reviewed-by: Kevin Tian <[email protected]> Link: https://lore.kernel.org/r/[email protected] Tested-by: Ido Schimmel <[email protected]> Signed-off-by: Joerg Roedel <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]>

anthraxx added the question Further information is requested label Jan 8, 2021

sydhds mentioned this issue Apr 6, 2023

sysctl conf for networking sydhds/hardenbuntu#23

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Question regarding sysctl network parameters #55

Question regarding sysctl network parameters #55

Utini2000 commented Dec 30, 2020

five23 commented Jul 18, 2021

Uh oh!

Question regarding sysctl network parameters #55

Question regarding sysctl network parameters #55

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Utini2000 commented Dec 30, 2020

five23 commented Jul 18, 2021

Uh oh!