Miscellaneous VFS2 fixes.

PiperOrigin-RevId: 316627764

3 files changed, 46 insertions, 11 deletions

diff --git a/pkg/sentry/fsimpl/gofer/gofer.go b/pkg/sentry/fsimpl/gofer/gofer.go
index 0d88a328e..ac051b3a7 100644
--- a/pkg/sentry/fsimpl/gofer/gofer.go
+++ b/pkg/sentry/fsimpl/gofer/gofer.go
@@ -835,6 +835,14 @@ func (d *dentry) statTo(stat *linux.Statx) {
 	stat.Mask = linux.STATX_TYPE | linux.STATX_MODE | linux.STATX_NLINK | linux.STATX_UID | linux.STATX_GID | linux.STATX_ATIME | linux.STATX_MTIME | linux.STATX_CTIME | linux.STATX_INO | linux.STATX_SIZE | linux.STATX_BLOCKS | linux.STATX_BTIME
 	stat.Blksize = atomic.LoadUint32(&d.blockSize)
 	stat.Nlink = atomic.LoadUint32(&d.nlink)
+	if stat.Nlink == 0 {
+		// The remote filesystem doesn't support link count; just make
+		// something up. This is consistent with Linux, where
+		// fs/inode.c:inode_init_always() initializes link count to 1, and
+		// fs/9p/vfs_inode_dotl.c:v9fs_stat2inode_dotl() doesn't touch it if
+		// it's not provided by the remote filesystem.
+		stat.Nlink = 1
+	}
 	stat.UID = atomic.LoadUint32(&d.uid)
 	stat.GID = atomic.LoadUint32(&d.gid)
 	stat.Mode = uint16(atomic.LoadUint32(&d.mode))
@@ -1346,23 +1354,21 @@ func (d *dentry) ensureSharedHandle(ctx context.Context, read, write, trunc bool
 }
 
 // incLinks increments link count.
-//
-// Preconditions: d.nlink != 0 && d.nlink < math.MaxUint32.
 func (d *dentry) incLinks() {
-	v := atomic.AddUint32(&d.nlink, 1)
-	if v < 2 {
-		panic(fmt.Sprintf("dentry.nlink is invalid (was 0 or overflowed): %d", v))
+	if atomic.LoadUint32(&d.nlink) == 0 {
+		// The remote filesystem doesn't support link count.
+		return
 	}
+	atomic.AddUint32(&d.nlink, 1)
 }
 
 // decLinks decrements link count.
-//
-// Preconditions: d.nlink > 1.
 func (d *dentry) decLinks() {
-	v := atomic.AddUint32(&d.nlink, ^uint32(0))
-	if v == 0 {
-		panic(fmt.Sprintf("dentry.nlink must be greater than 0: %d", v))
+	if atomic.LoadUint32(&d.nlink) == 0 {
+		// The remote filesystem doesn't support link count.
+		return
 	}
+	atomic.AddUint32(&d.nlink, ^uint32(0))
 }
 
 // fileDescription is embedded by gofer implementations of
diff --git a/pkg/sentry/kernel/kernel.go b/pkg/sentry/kernel/kernel.go
index bcbeb6a39..52491da7a 100644
--- a/pkg/sentry/kernel/kernel.go
+++ b/pkg/sentry/kernel/kernel.go
@@ -892,7 +892,7 @@ func (k *Kernel) CreateProcess(args CreateProcessArgs) (*ThreadGroup, ThreadID,
 		if mntnsVFS2 == nil {
 			// MountNamespaceVFS2 adds a reference to the namespace, which is
 			// transferred to the new process.
-			mntnsVFS2 = k.GlobalInit().Leader().MountNamespaceVFS2()
+			mntnsVFS2 = k.globalInit.Leader().MountNamespaceVFS2()
 		}
 		// Get the root directory from the MountNamespace.
 		root := args.MountNamespaceVFS2.Root()
diff --git a/pkg/sentry/syscalls/linux/vfs2/ioctl.go b/pkg/sentry/syscalls/linux/vfs2/ioctl.go
index 5a2418da9..0399c0db4 100644
--- a/pkg/sentry/syscalls/linux/vfs2/ioctl.go
+++ b/pkg/sentry/syscalls/linux/vfs2/ioctl.go
@@ -15,6 +15,7 @@
 package vfs2
 
 import (
+	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/sentry/arch"
 	"gvisor.dev/gvisor/pkg/sentry/kernel"
 	"gvisor.dev/gvisor/pkg/syserror"
@@ -30,6 +31,34 @@ func Ioctl(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Syscall
 	}
 	defer file.DecRef()
 
+	// Handle ioctls that apply to all FDs.
+	switch args[1].Int() {
+	case linux.FIONCLEX:
+		t.FDTable().SetFlagsVFS2(fd, kernel.FDFlags{
+			CloseOnExec: false,
+		})
+		return 0, nil, nil
+
+	case linux.FIOCLEX:
+		t.FDTable().SetFlagsVFS2(fd, kernel.FDFlags{
+			CloseOnExec: true,
+		})
+		return 0, nil, nil
+
+	case linux.FIONBIO:
+		var set int32
+		if _, err := t.CopyIn(args[2].Pointer(), &set); err != nil {
+			return 0, nil, err
+		}
+		flags := file.StatusFlags()
+		if set != 0 {
+			flags |= linux.O_NONBLOCK
+		} else {
+			flags &^= linux.O_NONBLOCK
+		}
+		return 0, nil, file.SetStatusFlags(t, t.Credentials(), flags)
+	}
+
 	ret, err := file.Ioctl(t, t.MemoryManager(), args)
 	return ret, nil, err
 }