1 files changed, 39 insertions, 16 deletions

diff --git a/pkg/sentry/fsimpl/tmpfs/regular_file.go b/pkg/sentry/fsimpl/tmpfs/regular_file.go
index f200e767d..e9e6faf67 100644
--- a/pkg/sentry/fsimpl/tmpfs/regular_file.go
+++ b/pkg/sentry/fsimpl/tmpfs/regular_file.go
@@ -20,17 +20,17 @@ import (
 	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
-	"gvisor.dev/gvisor/pkg/sentry/context"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/safemem"
 	"gvisor.dev/gvisor/pkg/sentry/fs/fsutil"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/memmap"
 	"gvisor.dev/gvisor/pkg/sentry/pgalloc"
-	"gvisor.dev/gvisor/pkg/sentry/safemem"
 	"gvisor.dev/gvisor/pkg/sentry/usage"
-	"gvisor.dev/gvisor/pkg/sentry/usermem"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
 )
 
 type regularFile struct {
@@ -63,13 +63,44 @@ func (fs *filesystem) newRegularFile(creds *auth.Credentials, mode linux.FileMod
 	return &file.inode
 }
 
+// truncate grows or shrinks the file to the given size. It returns true if the
+// file size was updated.
+func (rf *regularFile) truncate(size uint64) (bool, error) {
+	rf.mu.Lock()
+	defer rf.mu.Unlock()
+
+	if size == rf.size {
+		// Nothing to do.
+		return false, nil
+	}
+
+	if size > rf.size {
+		// Growing the file.
+		if rf.seals&linux.F_SEAL_GROW != 0 {
+			// Seal does not allow growth.
+			return false, syserror.EPERM
+		}
+		rf.size = size
+		return true, nil
+	}
+
+	// Shrinking the file
+	if rf.seals&linux.F_SEAL_SHRINK != 0 {
+		// Seal does not allow shrink.
+		return false, syserror.EPERM
+	}
+
+	// TODO(gvisor.dev/issues/1197): Invalidate mappings once we have
+	// mappings.
+
+	rf.data.Truncate(size, rf.memFile)
+	rf.size = size
+	return true, nil
+}
+
 type regularFileFD struct {
 	fileDescription
 
-	// These are immutable.
-	readable bool
-	writable bool
-
 	// off is the file offset. off is accessed using atomic memory operations.
 	// offMu serializes operations that may mutate off.
 	off   int64
@@ -78,16 +109,11 @@ type regularFileFD struct {
 
 // Release implements vfs.FileDescriptionImpl.Release.
 func (fd *regularFileFD) Release() {
-	if fd.writable {
-		fd.vfsfd.VirtualDentry().Mount().EndWrite()
-	}
+	// noop
 }
 
 // PRead implements vfs.FileDescriptionImpl.PRead.
 func (fd *regularFileFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
-	if !fd.readable {
-		return 0, syserror.EINVAL
-	}
 	if offset < 0 {
 		return 0, syserror.EINVAL
 	}
@@ -112,9 +138,6 @@ func (fd *regularFileFD) Read(ctx context.Context, dst usermem.IOSequence, opts
 
 // PWrite implements vfs.FileDescriptionImpl.PWrite.
 func (fd *regularFileFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
-	if !fd.writable {
-		return 0, syserror.EINVAL
-	}
 	if offset < 0 {
 		return 0, syserror.EINVAL
 	}