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net/tstun: make tun creation error diagnostic more container friendly

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Check for read/write permissions on /dev/net/tun before running
the modprobe check that almost always fail in containers.

Updates tailscale/tailscale#14277

Signed-off-by: Irbe Krumina <irbe@tailscale.com>
This commit is contained in:
Irbe Krumina 2024-12-04 15:18:21 +00:00
parent 2aac916888
commit eb0496441f
1 changed files with 9 additions and 1 deletions
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10
net/tstun/tun_linux.go
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@ -11,6 +11,7 @@ import (
"strings"
"syscall"
"golang.org/x/sys/unix"
"tailscale.com/types/logger"
"tailscale.com/version/distro"
)
@ -36,6 +37,14 @@ func diagnoseLinuxTUNFailure(tunName string, logf logger.Logf, createErr error)
kernel := utsReleaseField(&un)
logf("Linux kernel version: %s", kernel)
const dev = "/dev/net/tun"
// Check for read/write access to /dev/net/tun before the modprobe check because modprobe would almost always
// fail in containerized environments, see https://github.com/tailscale/tailscale/issues/14277
if err := unix.Access(dev, unix.O_RDWR); err != nil {
logf("tailscaled likely does not have read or write access to %q, access check failed with: %v", dev, err)
return
}
modprobeOut, err := exec.Command("/sbin/modprobe", "tun").CombinedOutput()
if err == nil {
logf("'modprobe tun' successful")
@ -45,7 +54,6 @@ func diagnoseLinuxTUNFailure(tunName string, logf logger.Logf, createErr error)
//
// So if there's a problem at this point, it's
// probably because /dev/net/tun doesn't exist.
const dev = "/dev/net/tun"
if fi, err := os.Stat(dev); err != nil {
logf("tun module loaded in kernel, but %s does not exist", dev)
} else {