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syscallcompat: deduplicate OpenatUser/MknodatUser/SymlinkatUser/MkdiratUser

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Turns out the whole euid switching logic can be shared when
wrapping the syscall in a closure.
This commit is contained in:
Jakob Unterwurzacher 2021-05-22 21:37:41 +02:00
parent 0650a512bb
commit cb4f9f9e29
1 changed files with 37 additions and 76 deletions
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113
internal/syscallcompat/sys_linux.go
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@ -91,11 +91,9 @@ func getSupplementaryGroups(pid uint32) (gids []int) {
return nil
}
// OpenatUser runs the Openat syscall in the context of a different user.
//
// It switches the current thread to the new user, performs the syscall,
// and switches back.
func OpenatUser(dirfd int, path string, flags int, mode uint32, context *fuse.Context) (fd int, err error) {
// asUser runs the function `f` under the effective uid, gid, groups specified
// in `context`.
func asUser(f func() (int, error), context *fuse.Context) (int, error) {
if context != nil {
runtime.LockOSThread()
defer runtime.UnlockOSThread()
@ -107,7 +105,7 @@ func OpenatUser(dirfd int, path string, flags int, mode uint32, context *fuse.Co
//
// We now use unix.{Setgroups,Setregid,Setreuid} instead.
err = unix.Setgroups(getSupplementaryGroups(context.Pid))
err := unix.Setgroups(getSupplementaryGroups(context.Pid))
if err != nil {
return -1, err
}
@ -125,8 +123,18 @@ func OpenatUser(dirfd int, path string, flags int, mode uint32, context *fuse.Co
}
defer unix.Setreuid(-1, 0)
}
return f()
}
return Openat(dirfd, path, flags, mode)
// OpenatUser runs the Openat syscall in the context of a different user.
//
// It switches the current thread to the new user, performs the syscall,
// and switches back.
func OpenatUser(dirfd int, path string, flags int, mode uint32, context *fuse.Context) (fd int, err error) {
f := func() (int, error) {
return Openat(dirfd, path, flags, mode)
}
return asUser(f, context)
}
// Mknodat wraps the Mknodat syscall.
@ -138,30 +146,12 @@ func Mknodat(dirfd int, path string, mode uint32, dev int) (err error) {
//
// See OpenatUser() for how this works.
func MknodatUser(dirfd int, path string, mode uint32, dev int, context *fuse.Context) (err error) {
if context != nil {
runtime.LockOSThread()
defer runtime.UnlockOSThread()
err = unix.Setgroups(getSupplementaryGroups(context.Pid))
if err != nil {
return err
}
defer unix.Setgroups(nil)
err = unix.Setregid(-1, int(context.Owner.Gid))
if err != nil {
return err
}
defer unix.Setregid(-1, 0)
err = unix.Setreuid(-1, int(context.Owner.Uid))
if err != nil {
return err
}
defer unix.Setreuid(-1, 0)
f := func() (int, error) {
err := Mknodat(dirfd, path, mode, dev)
return -1, err
}
return Mknodat(dirfd, path, mode, dev)
_, err = asUser(f, context)
return err
}
// Dup3 wraps the Dup3 syscall. We want to use Dup3 rather than Dup2 because Dup2
@ -208,60 +198,31 @@ func FchmodatNofollow(dirfd int, path string, mode uint32) (err error) {
//
// See OpenatUser() for how this works.
func SymlinkatUser(oldpath string, newdirfd int, newpath string, context *fuse.Context) (err error) {
if context != nil {
runtime.LockOSThread()
defer runtime.UnlockOSThread()
err = unix.Setgroups(getSupplementaryGroups(context.Pid))
if err != nil {
return err
}
defer unix.Setgroups(nil)
err = unix.Setregid(-1, int(context.Owner.Gid))
if err != nil {
return err
}
defer unix.Setregid(-1, 0)
err = unix.Setreuid(-1, int(context.Owner.Uid))
if err != nil {
return err
}
defer unix.Setreuid(-1, 0)
f := func() (int, error) {
err := Symlinkat(oldpath, newdirfd, newpath)
return -1, err
}
return Symlinkat(oldpath, newdirfd, newpath)
_, err = asUser(f, context)
return err
}
// MkdiratUser runs the Mkdirat syscall in the context of a different user.
//
// See OpenatUser() for how this works.
func MkdiratUser(dirfd int, path string, mode uint32, caller *fuse.Caller) (err error) {
if caller != nil {
runtime.LockOSThread()
defer runtime.UnlockOSThread()
err = unix.Setgroups(getSupplementaryGroups(caller.Pid))
if err != nil {
return err
}
defer unix.Setgroups(nil)
err = unix.Setregid(-1, int(caller.Gid))
if err != nil {
return err
}
defer unix.Setregid(-1, 0)
err = unix.Setreuid(-1, int(caller.Uid))
if err != nil {
return err
}
defer unix.Setreuid(-1, 0)
f := func() (int, error) {
err := Mkdirat(dirfd, path, mode)
return -1, err
}
return Mkdirat(dirfd, path, mode)
// TODO: refactor MkdiratUser to take context instead of caller
var context *fuse.Context
if caller != nil {
context = &fuse.Context{
Caller: *caller,
}
}
_, err = asUser(f, context)
return err
}
func timesToTimespec(a *time.Time, m *time.Time) []unix.Timespec {