Support setgid directories in tmpfs and kernfs

PiperOrigin-RevId: 356868412

1 files changed, 26 insertions, 7 deletions

diff --git a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
index 8139bff76..6b890a39c 100644
--- a/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
+++ b/pkg/sentry/fsimpl/kernfs/inode_impl_util.go
@@ -294,22 +294,41 @@ func (a *InodeAttrs) SetStat(ctx context.Context, fs *vfs.Filesystem, creds *aut
 		return err
 	}
 
+	clearSID := false
 	stat := opts.Stat
+	if stat.Mask&linux.STATX_UID != 0 {
+		atomic.StoreUint32(&a.uid, stat.UID)
+		clearSID = true
+	}
+	if stat.Mask&linux.STATX_GID != 0 {
+		atomic.StoreUint32(&a.gid, stat.GID)
+		clearSID = true
+	}
 	if stat.Mask&linux.STATX_MODE != 0 {
 		for {
 			old := atomic.LoadUint32(&a.mode)
-			new := old | uint32(stat.Mode & ^uint16(linux.S_IFMT))
-			if swapped := atomic.CompareAndSwapUint32(&a.mode, old, new); swapped {
+			ft := old & linux.S_IFMT
+			newMode := ft | uint32(stat.Mode & ^uint16(linux.S_IFMT))
+			if clearSID {
+				newMode = vfs.ClearSUIDAndSGID(newMode)
+			}
+			if swapped := atomic.CompareAndSwapUint32(&a.mode, old, newMode); swapped {
+				clearSID = false
 				break
 			}
 		}
 	}
 
-	if stat.Mask&linux.STATX_UID != 0 {
-		atomic.StoreUint32(&a.uid, stat.UID)
-	}
-	if stat.Mask&linux.STATX_GID != 0 {
-		atomic.StoreUint32(&a.gid, stat.GID)
+	// We may have to clear the SUID/SGID bits, but didn't do so as part of
+	// STATX_MODE.
+	if clearSID {
+		for {
+			old := atomic.LoadUint32(&a.mode)
+			newMode := vfs.ClearSUIDAndSGID(old)
+			if swapped := atomic.CompareAndSwapUint32(&a.mode, old, newMode); swapped {
+				break
+			}
+		}
 	}
 
 	now := ktime.NowFromContext(ctx).Nanoseconds()