Force timestamps to update when set via InodeOperations.SetTimestamps.

The gofer's CachingInodeOperations implementation contains an optimization for
the common open-read-close pattern when we have a host FD.  In this case, the
host kernel will update the timestamp for us to a reasonably close time, so we
don't need an extra RPC to the gofer.

However, when the app explicitly sets the timestamps (via futimes or similar)
then we actually DO need to update the timestamps, because the host kernel
won't do it for us.

To fix this, a new boolean `forceSetTimestamps` was added to
CachineInodeOperations.SetMaskedAttributes. It is only set by
gofer.InodeOperations.SetTimestamps.

PiperOrigin-RevId: 272048146

1 files changed, 14 insertions, 8 deletions

diff --git a/pkg/sentry/fs/fsutil/inode_cached.go b/pkg/sentry/fs/fsutil/inode_cached.go
index d404a79d4..dd80757dc 100644
--- a/pkg/sentry/fs/fsutil/inode_cached.go
+++ b/pkg/sentry/fs/fsutil/inode_cached.go
@@ -140,12 +140,16 @@ type CachedFileObject interface {
 	// WriteFromBlocksAt may return a partial write without an error.
 	WriteFromBlocksAt(ctx context.Context, srcs safemem.BlockSeq, offset uint64) (uint64, error)
 
-	// SetMaskedAttributes sets the attributes in attr that are true in mask
-	// on the backing file.
+	// SetMaskedAttributes sets the attributes in attr that are true in
+	// mask on the backing file. If the mask contains only ATime or MTime
+	// and the CachedFileObject has an FD to the file, then this operation
+	// is a noop unless forceSetTimestamps is true. This avoids an extra
+	// RPC to the gofer in the open-read/write-close case, when the
+	// timestamps on the file will be updated by the host kernel for us.
 	//
 	// SetMaskedAttributes may be called at any point, regardless of whether
 	// the file was opened.
-	SetMaskedAttributes(ctx context.Context, mask fs.AttrMask, attr fs.UnstableAttr) error
+	SetMaskedAttributes(ctx context.Context, mask fs.AttrMask, attr fs.UnstableAttr, forceSetTimestamps bool) error
 
 	// Allocate allows the caller to reserve disk space for the inode.
 	// It's equivalent to fallocate(2) with 'mode=0'.
@@ -224,7 +228,7 @@ func (c *CachingInodeOperations) SetPermissions(ctx context.Context, inode *fs.I
 
 	now := ktime.NowFromContext(ctx)
 	masked := fs.AttrMask{Perms: true}
-	if err := c.backingFile.SetMaskedAttributes(ctx, masked, fs.UnstableAttr{Perms: perms}); err != nil {
+	if err := c.backingFile.SetMaskedAttributes(ctx, masked, fs.UnstableAttr{Perms: perms}, false); err != nil {
 		return false
 	}
 	c.attr.Perms = perms
@@ -246,7 +250,7 @@ func (c *CachingInodeOperations) SetOwner(ctx context.Context, inode *fs.Inode,
 		UID: owner.UID.Ok(),
 		GID: owner.GID.Ok(),
 	}
-	if err := c.backingFile.SetMaskedAttributes(ctx, masked, fs.UnstableAttr{Owner: owner}); err != nil {
+	if err := c.backingFile.SetMaskedAttributes(ctx, masked, fs.UnstableAttr{Owner: owner}, false); err != nil {
 		return err
 	}
 	if owner.UID.Ok() {
@@ -282,7 +286,9 @@ func (c *CachingInodeOperations) SetTimestamps(ctx context.Context, inode *fs.In
 		AccessTime:       !ts.ATimeOmit,
 		ModificationTime: !ts.MTimeOmit,
 	}
-	if err := c.backingFile.SetMaskedAttributes(ctx, masked, fs.UnstableAttr{AccessTime: ts.ATime, ModificationTime: ts.MTime}); err != nil {
+	// Call SetMaskedAttributes with forceSetTimestamps = true to make sure
+	// the timestamp is updated.
+	if err := c.backingFile.SetMaskedAttributes(ctx, masked, fs.UnstableAttr{AccessTime: ts.ATime, ModificationTime: ts.MTime}, true); err != nil {
 		return err
 	}
 	if !ts.ATimeOmit {
@@ -305,7 +311,7 @@ func (c *CachingInodeOperations) Truncate(ctx context.Context, inode *fs.Inode,
 	now := ktime.NowFromContext(ctx)
 	masked := fs.AttrMask{Size: true}
 	attr := fs.UnstableAttr{Size: size}
-	if err := c.backingFile.SetMaskedAttributes(ctx, masked, attr); err != nil {
+	if err := c.backingFile.SetMaskedAttributes(ctx, masked, attr, false); err != nil {
 		c.dataMu.Unlock()
 		return err
 	}
@@ -394,7 +400,7 @@ func (c *CachingInodeOperations) WriteOut(ctx context.Context, inode *fs.Inode)
 	c.dirtyAttr.Size = false
 
 	// Write out cached attributes.
-	if err := c.backingFile.SetMaskedAttributes(ctx, c.dirtyAttr, c.attr); err != nil {
+	if err := c.backingFile.SetMaskedAttributes(ctx, c.dirtyAttr, c.attr, false); err != nil {
 		c.attrMu.Unlock()
 		return err
 	}