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net/dns: fall back to copy+delete/truncate if moving to/from /etc/resolv.conf fails.

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In some containers, /etc/resolv.conf is a bind-mount from outside the container.
This prevents renaming to or from /etc/resolv.conf, because it's on a different
filesystem from linux's perspective. It also prevents removing /etc/resolv.conf,
because doing so would break the bind-mount.

If we find ourselves within this environment, fall back to using copy+delete when
renaming to /etc/resolv.conf, and copy+truncate when renaming from /etc/resolv.conf.

Fixes #3000

Co-authored-by: Denton Gentry <dgentry@tailscale.com>
Signed-off-by: David Anderson <danderson@tailscale.com>
This commit is contained in:
David Anderson
2021-10-06 17:49:32 -07:00
committed by Dave Anderson
parent 04d24d3a38
commit a320d70614
8 changed files with 173 additions and 44 deletions
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8
net/dns/wsl_windows.go
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@ -99,9 +99,9 @@ func (wm *wslManager) SetDNS(cfg OSConfig) error {
} else if len(distros) == 0 {
return nil
}
managers := make(map[string]directManager)
managers := make(map[string]*directManager)
for _, distro := range distros {
managers[distro] = newDirectManagerOnFS(wslFS{
managers[distro] = newDirectManagerOnFS(wm.logf, wslFS{
user: "root",
distro: distro,
})
@ -141,7 +141,7 @@ generateResolvConf = false
// setWSLConf attempts to disable generateResolvConf in each WSL2 linux.
// If any are changed, it reports true.
func (wm *wslManager) setWSLConf(managers map[string]directManager) (changed bool) {
func (wm *wslManager) setWSLConf(managers map[string]*directManager) (changed bool) {
for distro, m := range managers {
b, err := m.fs.ReadFile(wslConf)
if err != nil && !os.IsNotExist(err) {
@ -189,6 +189,8 @@ func (fs wslFS) Rename(oldName, newName string) error {
}
func (fs wslFS) Remove(name string) error { return wslRun(fs.cmd("rm", "--", name)) }
func (fs wslFS) Truncate(name string) error { return fs.WriteFile(name, nil, 0644) }
func (fs wslFS) ReadFile(name string) ([]byte, error) {
b, err := wslCombinedOutput(fs.cmd("cat", "--", name))
if ee, _ := err.(*exec.ExitError); ee != nil && ee.ExitCode() == 1 {