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wgengine/router,util/kmod: load & log xt_mark

Browse Source 
Attempt to load the xt_mark kernel module when it is not present. If the
load fails, log error information.

It may be tempting to promote this failure to an error once it has been
in use for some time, so as to avoid reaching an error with the iptables
invocation, however, there are conditions under which the two stages may
disagree - this change adds more useful breadcrumbs.

Example new output from tailscaled running under my WSL2:

```
router: ensure module xt_mark: "/usr/sbin/modprobe xt_mark" failed: exit status 1; modprobe: FATAL: Module xt_mark not found in directory /lib/modules/5.10.43.3-microsoft-standard-WSL2
```

Background:

There are two places to lookup modules, one is `/proc/modules` "old",
the other is `/sys/module/` "new".

There was query_modules(2) in linux <2.6, alas, it is gone.

In a docker container in the default configuration, you would get
/proc/modules and /sys/module/ both populated. lsmod may work file,
modprobe will fail with EPERM at `finit_module()` for an unpriviliged
container.

In a priviliged container the load may *succeed*, if some conditions are
met. This condition should be avoided, but the code landing in this
change does not attempt to avoid this scenario as it is both difficult
to detect, and has a very uncertain impact.

In an nspawn container `/proc/modules` is populated, but `/sys/module`
does not exist. Modern `lsmod` versions will fail to gather most module
information, without sysfs being populated with module information.

In WSL2 modules are likely missing, as the in-use kernel typically is
not provided by the distribution filesystem, and WSL does not mount in a
module filesystem of its own. Notably the WSL2 kernel supports iptables
marks without listing the xt_mark module in /sys/module, and
/proc/modules is empty.

On a recent kernel, we can ask the capabilities system about SYS_MODULE,
that will help to disambiguate between the non-privileged container case
and just being root. On older kernels these calls may fail.

Update #4329

Signed-off-by: James Tucker <james@tailscale.com>
This commit is contained in:
James Tucker
2022-04-11 18:25:35 -07:00
committed by James Tucker
parent f7cb6630e7
commit 8d6793fd70
6 changed files with 225 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

9
go.sum
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@@ -1447,6 +1447,7 @@ golang.org/x/sys v0.0.0-20210220050731-9a76102bfb43/go.mod h1:h1NjWce9XRLGQEsW7w
golang.org/x/sys v0.0.0-20210301091718-77cc2087c03b/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20210303074136-134d130e1a04/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20210305230114-8fe3ee5dd75b/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20210309074719-68d13333faf2/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20210315160823-c6e025ad8005/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20210320140829-1e4c9ba3b0c4/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20210324051608-47abb6519492/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
@@ -1827,6 +1828,10 @@ inet.af/peercred v0.0.0-20210906144145-0893ea02156a h1:qdkS8Q5/i10xU2ArJMKYhVa1D
inet.af/peercred v0.0.0-20210906144145-0893ea02156a/go.mod h1:FjawnflS/udxX+SvpsMgZfdqx2aykOlkISeAsADi5IU=
inet.af/wf v0.0.0-20211204062712-86aaea0a7310 h1:0jKHTf+W75kYRyg5bto1UT+r18QmAz2u/5pAs/fx4zo=
inet.af/wf v0.0.0-20211204062712-86aaea0a7310/go.mod h1:ViGMZRA6+RA318D7GCncrjv5gHUrPYrNDejjU12tikA=
kernel.org/pub/linux/libs/security/libcap/cap v1.2.64 h1:E1U4GNGSXEdzQUT+mop0iYawCNXDUU46Y8nfodb+ZY0=
kernel.org/pub/linux/libs/security/libcap/cap v1.2.64/go.mod h1:gtBlgvjXflnxHng9/3bXyXG3XmBYKDt35zu+lNmB+IA=
kernel.org/pub/linux/libs/security/libcap/psx v1.2.64 h1:zlw/KoDjEObyddpFcvLiuu8frEvyEwVNc62WZQBp68w=
kernel.org/pub/linux/libs/security/libcap/psx v1.2.64/go.mod h1:+l6Ee2F59XiJ2I6WR5ObpC1utCQJZ/VLsEbQCD8RG24=
mvdan.cc/gofumpt v0.0.0-20200802201014-ab5a8192947d/go.mod h1:bzrjFmaD6+xqohD3KYP0H2FEuxknnBmyyOxdhLdaIws=
mvdan.cc/gofumpt v0.0.0-20201129102820-5c11c50e9475/go.mod h1:E4LOcu9JQEtnYXtB1Y51drqh2Qr2Ngk9J3YrRCwcbd0=
mvdan.cc/gofumpt v0.1.1/go.mod h1:yXG1r1WqZVKWbVRtBWKWX9+CxGYfA51nSomhM0woR48=
@@ -1842,6 +1847,10 @@ mvdan.cc/unparam v0.0.0-20211002134041-24922b6997ca h1:xzXXnoG5a3NUnKAcVMpE2cs3+
mvdan.cc/unparam v0.0.0-20211002134041-24922b6997ca/go.mod h1:Mb96j26qXgU/+SOj6MSgC36X30UgAlRYaxckYuYyEmo=
nhooyr.io/websocket v1.8.7 h1:usjR2uOr/zjjkVMy0lW+PPohFok7PCow5sDjLgX4P4g=
nhooyr.io/websocket v1.8.7/go.mod h1:B70DZP8IakI65RVQ51MsWP/8jndNma26DVA/nFSCgW0=
pault.ag/go/modprobe v0.1.2 h1:bblunaPhqpTxGDJ5TVFW/4gheohBPleF2dIV6j6sWkI=
pault.ag/go/modprobe v0.1.2/go.mod h1:afr2STC/2Maz/qi4+Bma1s0dszZgO/PcM8AKar9DWhM=
pault.ag/go/topsort v0.0.0-20160530003732-f98d2ad46e1a h1:WwS7vlB5H2AtwKj1jsGwp2ZLud1x6WXRXh2fXsRqrcA=
pault.ag/go/topsort v0.0.0-20160530003732-f98d2ad46e1a/go.mod h1:INqx0ClF7kmPAMk2zVTX8DRnhZ/yaA/Mg52g8KFKE7k=
rsc.io/binaryregexp v0.2.0/go.mod h1:qTv7/COck+e2FymRvadv62gMdZztPaShugOCi3I+8D8=
rsc.io/quote/v3 v3.1.0/go.mod h1:yEA65RcK8LyAZtP9Kv3t0HmxON59tX3rD+tICJqUlj0=
rsc.io/sampler v1.3.0/go.mod h1:T1hPZKmBbMNahiBKFy5HrXp6adAjACjK9JXDnKaTXpA=