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client: protect user lookups with global lock (#14742)
* client: protect user lookups with global lock This PR updates Nomad client to always do user lookups while holding a global process lock. This is to prevent concurrency unsafe implementations of NSS, but still enabling NSS lookups of users (i.e. cannot not use osusergo). * cl: add cl
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,3 @@ | ||
| ```release-note:improvement | ||
| client: re-enable nss-based user lookups | ||
| ``` |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,53 @@ | ||
| package users | ||
|
|
||
| import ( | ||
| "fmt" | ||
| "os/user" | ||
| "sync" | ||
| ) | ||
|
|
||
| // lock is used to serialize all user lookup at the process level, because | ||
| // some NSS implementations are not concurrency safe | ||
| var lock *sync.Mutex | ||
|
|
||
| // nobody is a cached copy of the nobody user, which is going to be looked-up | ||
| // frequently and is unlikely to be modified on the underlying system. | ||
| var nobody user.User | ||
|
|
||
| // Nobody returns User data for the "nobody" user on the system, bypassing the | ||
| // locking / file read / NSS lookup. | ||
| func Nobody() user.User { | ||
| // original is immutable via copy by value | ||
| return nobody | ||
| } | ||
|
|
||
| func init() { | ||
| lock = new(sync.Mutex) | ||
| u, err := Lookup("nobody") | ||
| if err != nil { | ||
| panic(fmt.Sprintf("unable to lookup the nobody user: %v", err)) | ||
| } | ||
| nobody = *u | ||
| } | ||
|
|
||
| // Lookup username while holding a global process lock. | ||
| func Lookup(username string) (*user.User, error) { | ||
| lock.Lock() | ||
| defer lock.Unlock() | ||
| return user.Lookup(username) | ||
| } | ||
|
|
||
| // LookupGroupId while holding a global process lock. | ||
| func LookupGroupId(gid string) (*user.Group, error) { | ||
| lock.Lock() | ||
| defer lock.Unlock() | ||
| return user.LookupGroupId(gid) | ||
| } | ||
|
|
||
| // Current returns the current user, acquired while holding a global process | ||
| // lock. | ||
| func Current() (*user.User, error) { | ||
| lock.Lock() | ||
| defer lock.Unlock() | ||
| return user.Current() | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,35 @@ | ||
| //go:build linux | ||
|
|
||
| package users | ||
|
|
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| import ( | ||
| "errors" | ||
| "os/user" | ||
| "testing" | ||
|
|
||
| "github.com/shoenig/test/must" | ||
| ) | ||
|
|
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| func TestLookup(t *testing.T) { | ||
| cases := []struct { | ||
| username string | ||
|
|
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| expErr error | ||
| expUser *user.User | ||
| }{ | ||
| {username: "nobody", expUser: &user.User{Username: "nobody", Uid: "65534", Gid: "65534", Name: "nobody", HomeDir: "/nonexistent"}}, // ubuntu | ||
| {username: "root", expUser: &user.User{Username: "root", Uid: "0", Gid: "0", Name: "root", HomeDir: "/root"}}, | ||
| {username: "doesnotexist", expErr: errors.New("user: unknown user doesnotexist")}, | ||
| } | ||
|
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||
| for _, tc := range cases { | ||
| t.Run(tc.username, func(t *testing.T) { | ||
| u, err := Lookup(tc.username) | ||
| if tc.expErr != nil { | ||
| must.EqError(t, tc.expErr, err.Error()) | ||
| } else { | ||
| must.Eq(t, tc.expUser, u) | ||
| } | ||
| }) | ||
| } | ||
| } |