Implement flock(2) in VFS2

LockFD is the generic implementation that can be embedded in
FileDescriptionImpl implementations. Unique lock ID is
maintained in vfs.FileDescription and is created on demand.

Updates #1480

PiperOrigin-RevId: 315604825

4 files changed, 12 insertions, 22 deletions

diff --git a/pkg/sentry/kernel/fd_table.go b/pkg/sentry/kernel/fd_table.go
index dbfcef0fa..b35afafe3 100644
--- a/pkg/sentry/kernel/fd_table.go
+++ b/pkg/sentry/kernel/fd_table.go
@@ -80,9 +80,6 @@ type FDTable struct {
 	refs.AtomicRefCount
 	k *Kernel
 
-	// uid is a unique identifier.
-	uid uint64
-
 	// mu protects below.
 	mu sync.Mutex `state:"nosave"`
 
@@ -130,7 +127,7 @@ func (f *FDTable) loadDescriptorTable(m map[int32]descriptor) {
 // drop drops the table reference.
 func (f *FDTable) drop(file *fs.File) {
 	// Release locks.
-	file.Dirent.Inode.LockCtx.Posix.UnlockRegion(lock.UniqueID(f.uid), lock.LockRange{0, lock.LockEOF})
+	file.Dirent.Inode.LockCtx.Posix.UnlockRegion(f, lock.LockRange{0, lock.LockEOF})
 
 	// Send inotify events.
 	d := file.Dirent
@@ -164,17 +161,9 @@ func (f *FDTable) dropVFS2(file *vfs.FileDescription) {
 	file.DecRef()
 }
 
-// ID returns a unique identifier for this FDTable.
-func (f *FDTable) ID() uint64 {
-	return f.uid
-}
-
 // NewFDTable allocates a new FDTable that may be used by tasks in k.
 func (k *Kernel) NewFDTable() *FDTable {
-	f := &FDTable{
-		k:   k,
-		uid: atomic.AddUint64(&k.fdMapUids, 1),
-	}
+	f := &FDTable{k: k}
 	f.init()
 	return f
 }
diff --git a/pkg/sentry/kernel/kernel.go b/pkg/sentry/kernel/kernel.go
index 5efeb3767..bcbeb6a39 100644
--- a/pkg/sentry/kernel/kernel.go
+++ b/pkg/sentry/kernel/kernel.go
@@ -194,11 +194,6 @@ type Kernel struct {
 	// cpuClockTickerSetting is protected by runningTasksMu.
 	cpuClockTickerSetting ktime.Setting
 
-	// fdMapUids is an ever-increasing counter for generating FDTable uids.
-	//
-	// fdMapUids is mutable, and is accessed using atomic memory operations.
-	fdMapUids uint64
-
 	// uniqueID is used to generate unique identifiers.
 	//
 	// uniqueID is mutable, and is accessed using atomic memory operations.
diff --git a/pkg/sentry/kernel/pipe/BUILD b/pkg/sentry/kernel/pipe/BUILD
index 7bfa9075a..0db546b98 100644
--- a/pkg/sentry/kernel/pipe/BUILD
+++ b/pkg/sentry/kernel/pipe/BUILD
@@ -27,6 +27,7 @@ go_library(
         "//pkg/sentry/fs",
         "//pkg/sentry/fs/fsutil",
         "//pkg/sentry/vfs",
+        "//pkg/sentry/vfs/lock",
         "//pkg/sync",
         "//pkg/syserror",
         "//pkg/usermem",
diff --git a/pkg/sentry/kernel/pipe/vfs.go b/pkg/sentry/kernel/pipe/vfs.go
index 2602bed72..c0e9ee1f4 100644
--- a/pkg/sentry/kernel/pipe/vfs.go
+++ b/pkg/sentry/kernel/pipe/vfs.go
@@ -21,6 +21,7 @@ import (
 	"gvisor.dev/gvisor/pkg/safemem"
 	"gvisor.dev/gvisor/pkg/sentry/arch"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/sentry/vfs/lock"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/syserror"
 	"gvisor.dev/gvisor/pkg/usermem"
@@ -61,11 +62,13 @@ func NewVFSPipe(isNamed bool, sizeBytes, atomicIOBytes int64) *VFSPipe {
 //
 // Preconditions: statusFlags should not contain an open access mode.
 func (vp *VFSPipe) ReaderWriterPair(mnt *vfs.Mount, vfsd *vfs.Dentry, statusFlags uint32) (*vfs.FileDescription, *vfs.FileDescription) {
-	return vp.newFD(mnt, vfsd, linux.O_RDONLY|statusFlags), vp.newFD(mnt, vfsd, linux.O_WRONLY|statusFlags)
+	// Connected pipes share the same locks.
+	locks := &lock.FileLocks{}
+	return vp.newFD(mnt, vfsd, linux.O_RDONLY|statusFlags, locks), vp.newFD(mnt, vfsd, linux.O_WRONLY|statusFlags, locks)
 }
 
 // Open opens the pipe represented by vp.
-func (vp *VFSPipe) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, statusFlags uint32) (*vfs.FileDescription, error) {
+func (vp *VFSPipe) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, statusFlags uint32, locks *lock.FileLocks) (*vfs.FileDescription, error) {
 	vp.mu.Lock()
 	defer vp.mu.Unlock()
 
@@ -75,7 +78,7 @@ func (vp *VFSPipe) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, s
 		return nil, syserror.EINVAL
 	}
 
-	fd := vp.newFD(mnt, vfsd, statusFlags)
+	fd := vp.newFD(mnt, vfsd, statusFlags, locks)
 
 	// Named pipes have special blocking semantics during open:
 	//
@@ -127,10 +130,11 @@ func (vp *VFSPipe) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, s
 }
 
 // Preconditions: vp.mu must be held.
-func (vp *VFSPipe) newFD(mnt *vfs.Mount, vfsd *vfs.Dentry, statusFlags uint32) *vfs.FileDescription {
+func (vp *VFSPipe) newFD(mnt *vfs.Mount, vfsd *vfs.Dentry, statusFlags uint32, locks *lock.FileLocks) *vfs.FileDescription {
 	fd := &VFSPipeFD{
 		pipe: &vp.pipe,
 	}
+	fd.LockFD.Init(locks)
 	fd.vfsfd.Init(fd, statusFlags, mnt, vfsd, &vfs.FileDescriptionOptions{
 		DenyPRead:         true,
 		DenyPWrite:        true,
@@ -159,6 +163,7 @@ type VFSPipeFD struct {
 	vfsfd vfs.FileDescription
 	vfs.FileDescriptionDefaultImpl
 	vfs.DentryMetadataFileDescriptionImpl
+	vfs.LockFD
 
 	pipe *Pipe
 }