When I added support to allow generic netlink multicast groups to be
restricted to subscribers with CAP_NET_ADMIN I was unaware that a
genl_bind implementation already existed in the past.

It was reverted due to ABBA deadlock:

1. ->netlink_bind gets called with the table lock held.
2. genetlink bind callback is invoked, it grabs the genl lock.

But when a new genl subsystem is (un)registered, these two locks are
taken in reverse order.

One solution would be to revert again and add a comment in genl
referring 1e82a62f, "genetlink: remove genl_bind").

This would need a second change in mptcp to not expose the raw token
value anymore, e.g.  by hashing the token with a secret key so userspace
can still associate subflow events with the correct mptcp connection.

However, Paolo Abeni reminded me to double-check why the netlink table is
locked in the first place.

I can't find one.  netlink_bind() is already called without this lock
when userspace joins a group via NETLINK_ADD_MEMBERSHIP setsockopt.
Same holds for the netlink_unbind operation.

Digging through the history, commit f7736080
("netlink: access nlk groups safely in netlink bind and getname")
expanded the lock scope.

commit 3a20773b ("net: netlink: cap max groups which will be considered in netlink_bind()")
... removed the nlk->ngroups access that the lock scope
extension was all about.

Reduce the lock scope again and always call ->netlink_bind without
the table lock.

The Fixes tag should be vs. the patch mentioned in the link below,
but that one got squash-merged into the patch that came earlier in the
series.

Fixes: 4d54cc32 ("mptcp: avoid lock_fast usage in accept path")
Link: https://lore.kernel.org/mptcp/20210213000001.379332-8-mathew.j.martineau@linux.intel.com/T/#u


Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Xin Long <lucien.xin@gmail.com>
Cc: Johannes Berg <johannes.berg@intel.com>
Cc: Sean Tranchetti <stranche@codeaurora.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

Daniel Borkmann says:

====================
pull-request: bpf 2021-04-17

The following pull-request contains BPF updates for your *net* tree.

We've added 10 non-merge commits during the last 9 day(s) which contain
a total of 8 files changed, 175 insertions(+), 111 deletions(-).

The main changes are:

1) Fix a potential NULL pointer dereference in libbpf's xsk
   umem handling, from Ciara Loftus.

2) Mitigate a speculative oob read of up to map value size by
   tightening the masking window, from Daniel Borkmann.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

Update my email and change myself to Reviewer.

Signed-off-by: Lijun Pan <lijunp213@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Update various selftest error messages:

 * The 'Rx tried to sub from different maps, paths, or prohibited types'
   is reworked into more specific/differentiated error messages for better
   guidance.

 * The change into 'value -4294967168 makes map_value pointer be out of
   bounds' is due to moving the mixed bounds check into the speculation
   handling and thus occuring slightly later than above mentioned sanity
   check.

 * The change into 'math between map_value pointer and register with
   unbounded min value' is similarly due to register sanity check coming
   before the mixed bounds check.

 * The case of 'map access: known scalar += value_ptr from different maps'
   now loads fine given masks are the same from the different paths (despite
   max map value size being different).

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>

This work tightens the offset mask we use for unprivileged pointer arithmetic
in order to mitigate a corner case reported by Piotr and Benedict where in
the speculative domain it is possible to advance, for example, the map value
pointer by up to value_size-1 out-of-bounds in order to leak kernel memory
via side-channel to user space.

Before this change, the computed ptr_limit for retrieve_ptr_limit() helper
represents largest valid distance when moving pointer to the right or left
which is then fed as aux->alu_limit to generate masking instructions against
the offset register. After the change, the derived aux->alu_limit represents
the largest potential value of the offset register which we mask against which
is just a narrower subset of the former limit.

For minimal complexity, we call sanitize_ptr_alu() from 2 observation points
in adjust_ptr_min_max_vals(), that is, before and after the simulated alu
operation. In the first step, we retieve the alu_state and alu_limit before
the operation as well as we branch-off a verifier path and push it to the
verification stack as we did before which checks the dst_reg under truncation,
in other words, when the speculative domain would attempt to move the pointer
out-of-bounds.

In the second step, we retrieve the new alu_limit and calculate the absolute
distance between both. Moreover, we commit the alu_state and final alu_limit
via update_alu_sanitation_state() to the env's instruction aux data, and bail
out from there if there is a mismatch due to coming from different verification
paths with different states.

Reported-by: Piotr Krysiuk <piotras@gmail.com>
Reported-by: Benedict Schlueter <benedict.schlueter@rub.de>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Benedict Schlueter <benedict.schlueter@rub.de>

Add a small sanitize_needed() helper function and move sanitize_val_alu()
out of the main opcode switch. In upcoming work, we'll move sanitize_ptr_alu()
as well out of its opcode switch so this helps to streamline both.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>

Move the bounds check in adjust_ptr_min_max_vals() into a small helper named
sanitize_check_bounds() in order to simplify the former a bit.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>

Consolidate all error handling and provide more user-friendly error messages
from sanitize_ptr_alu() and sanitize_val_alu().

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>

Small refactor with no semantic changes in order to consolidate the max
ptr_limit boundary check.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>

The mixed signed bounds check really belongs into retrieve_ptr_limit()
instead of outside of it in adjust_ptr_min_max_vals(). The reason is
that this check is not tied to PTR_TO_MAP_VALUE only, but to all pointer
types that we handle in retrieve_ptr_limit() and given errors from the latter
propagate back to adjust_ptr_min_max_vals() and lead to rejection of the
program, it's a better place to reside to avoid anything slipping through
for future types. The reason why we must reject such off_reg is that we
otherwise would not be able to derive a mask, see details in 9d7eceed


("bpf: restrict unknown scalars of mixed signed bounds for unprivileged").

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>

Small refactor to drag off_reg into sanitize_ptr_alu(), so we later on can
use off_reg for generalizing some of the checks for all pointer types.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>

We forbid adding unknown scalars with mixed signed bounds due to the
spectre v1 masking mitigation. Hence this also needs bypass_spec_v1
flag instead of allow_ptr_leaks.

Fixes: 2c78ee89

 ("bpf: Implement CAP_BPF")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>

Vinay Kumar Yadav says:

====================
chelsio/ch_ktls: chelsio inline tls driver bug fixes

This series of patches fix following bugs in Chelsio inline tls driver.
Patch1: kernel panic.
Patch2: connection close issue.
Patch3: tcb close call issue.
Patch4: unnecessary snd_una update.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

snd_una update should not be done when the same skb is being
sent out.chcr_short_record_handler() sends it again even
though SND_UNA update is already sent for the skb in
chcr_ktls_xmit(), which causes mismatch in un-acked
TCP seq number, later causes problem in sending out
complete record.

Fixes: 429765a1

 ("chcr: handle partial end part of a record")
Signed-off-by: Vinay Kumar Yadav <vinay.yadav@chelsio.com>
Signed-off-by: Rohit Maheshwari <rohitm@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

HW doesn't need marking TCB closed. This TCB state change
sometimes causes problem to the new connection which gets
the same tid.

Fixes: 34aba2c4

 ("cxgb4/chcr : Register to tls add and del callback")
Signed-off-by: Vinay Kumar Yadav <vinay.yadav@chelsio.com>
Signed-off-by: Rohit Maheshwari <rohitm@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

When sge queue is full and chcr_ktls_xmit_wr_complete()
returns failure, skb is not freed if it is not the last tls record in
this skb, causes refcount never gets freed and tls_dev_del()
never gets called on this connection.

Fixes: 5a4b9fe7

 ("cxgb4/chcr: complete record tx handling")
Signed-off-by: Vinay Kumar Yadav <vinay.yadav@chelsio.com>
Signed-off-by: Rohit Maheshwari <rohitm@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Taking page refcount is not ideal and causes kernel panic
sometimes. It's better to take tx_ctx lock for the complete
skb transmit, to avoid page cleanup if ACK received in middle.

Fixes: 5a4b9fe7

 ("cxgb4/chcr: complete record tx handling")
Signed-off-by: Vinay Kumar Yadav <vinay.yadav@chelsio.com>
Signed-off-by: Rohit Maheshwari <rohitm@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Saeed Mahameed says:

====================
mlx5 fixes 2021-04-14

This series provides 3 small fixes to mlx5 driver.
Please pull and let me know if there is any problem.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

Fix this panic by adding more rules to calculate the value of @rss_size_max
which could be used in allocating the queues when bpf is loaded, which,
however, could cause the failure and then trigger the NULL pointer of
vsi->rx_rings. Prio to this fix, the machine doesn't care about how many
cpus are online and then allocates 256 queues on the machine with 32 cpus
online actually.

Once the load of bpf begins, the log will go like this "failed to get
tracking for 256 queues for VSI 0 err -12" and this "setup of MAIN VSI
failed".

Thus, I attach the key information of the crash-log here.

BUG: unable to handle kernel NULL pointer dereference at
0000000000000000
RIP: 0010:i40e_xdp+0xdd/0x1b0 [i40e]
Call Trace:
[2160294.717292]  ? i40e_reconfig_rss_queues+0x170/0x170 [i40e]
[2160294.717666]  dev_xdp_install+0x4f/0x70
[2160294.718036]  dev_change_xdp_fd+0x11f/0x230
[2160294.718380]  ? dev_disable_lro+0xe0/0xe0
[2160294.718705]  do_setlink+0xac7/0xe70
[2160294.719035]  ? __nla_parse+0xed/0x120
[2160294.719365]  rtnl_newlink+0x73b/0x860

Fixes: 41c445ff

 ("i40e: main driver core")
Co-developed-by: Shujin Li <lishujin@kuaishou.com>
Signed-off-by: Shujin Li <lishujin@kuaishou.com>
Signed-off-by: Jason Xing <xingwanli@kuaishou.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

In the nft_offload there is the mate flow_dissector with no
ingress_ifindex but with ingress_iftype that only be used
in the software. So if the mask of ingress_ifindex in meta is
0, this meta check should be bypass.

Fixes: 6d65bc64

 ("net/mlx5e: Add mlx5e_flower_parse_meta support")
Signed-off-by: wenxu <wenxu@ucloud.cn>
Acked-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

Change register setting from bit number to bit mask.

Fixes: b5ede32d

 ("net/mlx5e: Add support for FEC modes based on 50G per lane links")
Signed-off-by: Aya Levin <ayal@nvidia.com>
Reviewed-by: Eran Ben Elisha <eranbe@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

Prevent setting of devlink traps on the uplink while in switchdev mode.
In this mode, it is the SW switch responsibility to handle both packets
with a mismatch in destination MAC or VLAN ID. Therefore, there are no
flow steering tables to trap undesirable packets and driver crashes upon
setting a trap.

Fixes: 241dc159

 ("net/mlx5: Notify on trap action by blocking event")
Signed-off-by: Aya Levin <ayal@nvidia.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

Tony Nguyen says:

====================
Intel Wired LAN Driver Updates 2021-04-14

This series contains updates to ixgbe and ice drivers.

Alex Duyck fixes a NULL pointer dereference for ixgbe.

Yongxin Liu fixes an unbalanced enable/disable which was causing a call
trace with suspend for ixgbe.

Colin King fixes a potential infinite loop for ice.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

This reverts commit 9c63faaa, which
introduces a suspend/resume regression on Jetson TX2 boards that can be
reproduced every time. Given that the issue that this was supposed to
fix only occurs very sporadically the safest course of action is to
revert before v5.12 and then we can have another go at fixing the more
rare issue in the next release (and perhaps backport it if necessary).

The root cause of the observed problem seems to be that when the system
is suspended, some packets are still in transit. When the descriptors
for these buffers are cleared on resume, the descriptors become invalid
and cause a fatal bus error.

Link: https://lore.kernel.org/r/708edb92-a5df-ecc4-3126-5ab36707e275@nvidia.com/


Reported-by: Jonathan Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Fix the following coccicheck warning:

./drivers/net/ethernet/cavium/liquidio/cn66xx_regs.h:413:6-28:
duplicated argument to & or |

The CN6XXX_INTR_M1UPB0_ERR here is duplicate.
Here should be CN6XXX_INTR_M1UNB0_ERR.

Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Commit a14d273b ("net: macb: restore cmp registers on resume path")
introduces the restore of CMP registers on resume path. In case the IP
doesn't support type 2 screeners (zero on DCFG8 register) the
struct macb::rx_fs_list::list is not initialized and thus the
list_for_each_entry(item, &bp->rx_fs_list.list, list) loop introduced in
commit a14d273b ("net: macb: restore cmp registers on resume path")
will access an uninitialized list leading to crash. Thus, initialize
the struct macb::rx_fs_list::list without taking into account if the
IP supports type 2 screeners or not.

Fixes: a14d273b

 ("net: macb: restore cmp registers on resume path")
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

This is a leftover of the below commit.

Fixes: 4f04256c

 ("net: vrf: Drop local rtable and rt6_info")
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Acked-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Let's have all seg6 sysctl at the same place.

Fixes: a6dc6670

 ("ipv6: sr: Add documentation for seg_flowlabel sysctl")
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Lijun Pan says:

====================
ibmvnic: correctly call NAPI APIs

This series correct some misuse of NAPI APIs in the driver.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

Remove the unnecessary napi_schedule() call in __ibmvnic_open() since
interrupt_rx() calls napi_schedule_prep/__napi_schedule during every
receive interrupt.

Fixes: ed651a10

 ("ibmvnic: Updated reset handling")
Signed-off-by: Lijun Pan <lijunp213@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

During adapter reset, do_reset/do_hard_reset calls ibmvnic_open(),
which will calls napi_schedule if previous state is VNIC_CLOSED
(i.e, the reset case, and "ifconfig down" case). So there is no need
for do_reset to call napi_schedule again at the end of the function
though napi_schedule will neglect the request if napi is already
scheduled.

Fixes: ed651a10

 ("ibmvnic: Updated reset handling")
Signed-off-by: Lijun Pan <lijunp213@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

__ibmvnic_open calls napi_disable without checking whether NAPI polling
has already been disabled or not. This could cause napi_disable
being called twice, which could generate deadlock. For example,
the first napi_disable will spin until NAPI_STATE_SCHED is cleared
by napi_complete_done, then set it again.
When napi_disable is called the second time, it will loop infinitely
because no dev->poll will be running to clear NAPI_STATE_SCHED.

To prevent above scenario from happening, call ibmvnic_napi_disable()
which checks if napi is disabled or not before calling napi_disable.

Fixes: bfc32f29

 ("ibmvnic: Move resource initialization to its own routine")
Suggested-by: Thomas Falcon <tlfalcon@linux.ibm.com>
Signed-off-by: Lijun Pan <lijunp213@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

It has been reported [0] that using pause frames in jumbo mode impacts
performance. There's no available chip documentation, but vendor
drivers r8168 and r8125 don't advertise pause in jumbo mode. So let's
do the same, according to Roman it fixes the issue.

[0] https://bugzilla.kernel.org/show_bug.cgi?id=212617

Fixes: 9cf9b84c

 ("r8169: make use of phy_set_asym_pause")
Reported-by: Roman Mamedov <rm+bko@romanrm.net>
Tested-by: Roman Mamedov <rm+bko@romanrm.net>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>

The intention was for pause statistics to not be reported
when driver does not have the relevant callback (only
report an empty netlink nest). What happens currently
we report all 0s instead. Make sure statistics are
initialized to "not set" (which is -1) so the dumping
code skips them.

Fixes: 9a27a330

 ("ethtool: add standard pause stats")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

The logic in connect() is currently written with the assumption that
xenbus_watch_pathfmt() will return an error for a node that does not
exist.  This assumption is incorrect: xenstore does allow a watch to
be registered for a nonexistent node (and will send notifications
should the node be subsequently created).

As of commit 1f256578

 ("xen-netback: remove 'hotplug-status' once it
has served its purpose"), this leads to a failure when a domU
transitions into XenbusStateConnected more than once.  On the first
domU transition into Connected state, the "hotplug-status" node will
be deleted by the hotplug_status_changed() callback in dom0.  On the
second or subsequent domU transition into Connected state, the
hotplug_status_changed() callback will therefore never be invoked, and
so the backend will remain stuck in InitWait.

This failure prevents scenarios such as reloading the xen-netfront
module within a domU, or booting a domU via iPXE.  There is
unfortunately no way for the domU to work around this dom0 bug.

Fix by explicitly checking for existence of the "hotplug-status" node,
thereby creating the behaviour that was previously assumed to exist.

Signed-off-by: Michael Brown <mbrown@fensystems.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

After commit 0f6925b3 ("virtio_net: Do not pull payload in skb->head")
Guenter Roeck reported one failure in his tests using sh architecture.

After much debugging, we have been able to spot silent unaligned accesses
in inet_gro_receive()

The issue at hand is that upper networking stacks assume their header
is word-aligned. Low level drivers are supposed to reserve NET_IP_ALIGN
bytes before the Ethernet header to make that happen.

This patch hardens skb_gro_reset_offset() to not allow frag0 fast-path
if the fragment is not properly aligned.

Some arches like x86, arm64 and powerpc do not care and define NET_IP_ALIGN
as 0, this extra check will be a NOP for them.

Note that if frag0 is not used, GRO will call pskb_may_pull()
as many times as needed to pull network and transport headers.

Fixes: 0f6925b3 ("virtio_net: Do not pull payload in skb->head")
Fixes: 78a478d0

 ("gro: Inline skb_gro_header and cache frag0 virtual address")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Guenter Roeck <linux@roeck-us.net>
Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

If sctp_destroy_sock is called without sock_net(sk)->sctp.addr_wq_lock
held and sp->do_auto_asconf is true, then an element is removed
from the auto_asconf_splist without any proper locking.

This can happen in the following functions:
1. In sctp_accept, if sctp_sock_migrate fails.
2. In inet_create or inet6_create, if there is a bpf program
   attached to BPF_CGROUP_INET_SOCK_CREATE which denies
   creation of the sctp socket.

The bug is fixed by acquiring addr_wq_lock in sctp_destroy_sock
instead of sctp_close.

This addresses CVE-2021-23133.

Reported-by: Or Cohen <orcohen@paloaltonetworks.com>
Reviewed-by: Xin Long <lucien.xin@gmail.com>
Fixes: 61023658

 ("bpf: Add new cgroup attach type to enable sock modifications")
Signed-off-by: Or Cohen <orcohen@paloaltonetworks.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

It is more correct to use dev_kfree_skb_irq when packets are dropped,
and to use dev_consume_skb_irq when packets are consumed.

Fixes: 0d973388

 ("ibmvnic: Introduce xmit_more support using batched subCRQ hcalls")
Suggested-by: Thomas Falcon <tlfalcon@linux.ibm.com>
Signed-off-by: Lijun Pan <lijunp213@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Currently, tcp_allowed_congestion_control is global and writable;
writing to it in any net namespace will leak into all other net
namespaces.

tcp_available_congestion_control and tcp_allowed_congestion_control are
the only sysctls in ipv4_net_table (the per-netns sysctl table) with a
NULL data pointer; their handlers (proc_tcp_available_congestion_control
and proc_allowed_congestion_control) have no other way of referencing a
struct net. Thus, they operate globally.

Because ipv4_net_table does not use designated initializers, there is no
easy way to fix up this one "bad" table entry. However, the data pointer
updating logic shouldn't be applied to NULL pointers anyway, so we
instead force these entries to be read-only.

These sysctls used to exist in ipv4_table (init-net only), but they were
moved to the per-net ipv4_net_table, presumably without realizing that
tcp_allowed_congestion_control was writable and thus introduced a leak.

Because the intent of that commit was only to know (i.e. read) "which
congestion algorithms are available or allowed", this read-only solution
should be sufficient.

The logic added in recent commit
31c4d2f1: ("net: Ensure net namespace isolation of sysctls")
does not and cannot check for NULL data pointers, because
other table entries (e.g. /proc/sys/net/netfilter/nf_log/) have
.data=NULL but use other methods (.extra2) to access the struct net.

Fixes: 9cb8e048

 ("net/ipv4/sysctl: show tcp_{allowed, available}_congestion_control in non-initial netns")
Signed-off-by: Jonathon Reinhart <jonathon.reinhart@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Hristo Venev says:

====================
net: Fix two use-after-free bugs

The two patches fix two use-after-free bugs related to cleaning up
network namespaces, one in sit and one in ip6_tunnel. They are easy to
trigger if the user has the ability to create network namespaces.

The bugs can be used to trigger null pointer dereferences. I am not
sure if they can be exploited further, but I would guess that they
can. I am not sending them to the mailing list without confirmation
that doing so would be OK.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>