Implement access/faccessat for VFS2.

Note that the raw faccessat system call does not actually take a flags argument;
according to faccessat(2), the glibc wrapper implements the flags by using
fstatat(2). Remove the flag argument that we try to extract from vfs1, which
would just be a garbage value.

Updates #1965
Fixes #2101

PiperOrigin-RevId: 300796067

4 files changed, 49 insertions, 0 deletions

diff --git a/pkg/sentry/fsimpl/ext/filesystem.go b/pkg/sentry/fsimpl/ext/filesystem.go
index e05429d41..8497be615 100644
--- a/pkg/sentry/fsimpl/ext/filesystem.go
+++ b/pkg/sentry/fsimpl/ext/filesystem.go
@@ -22,6 +22,7 @@ import (
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/fspath"
 	"gvisor.dev/gvisor/pkg/sentry/fsimpl/ext/disklayout"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/syserror"
@@ -255,6 +256,15 @@ func (fs *filesystem) statTo(stat *linux.Statfs) {
 	// TODO(b/134676337): Set Statfs.Flags and Statfs.FSID.
 }
 
+// AccessAt implements vfs.Filesystem.Impl.AccessAt.
+func (fs *filesystem) AccessAt(ctx context.Context, rp *vfs.ResolvingPath, creds *auth.Credentials, ats vfs.AccessTypes) error {
+	_, inode, err := fs.walk(rp, false)
+	if err != nil {
+		return err
+	}
+	return inode.checkPermissions(rp.Credentials(), ats)
+}
+
 // GetDentryAt implements vfs.FilesystemImpl.GetDentryAt.
 func (fs *filesystem) GetDentryAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.GetDentryOptions) (*vfs.Dentry, error) {
 	vfsd, inode, err := fs.walk(rp, false)
diff --git a/pkg/sentry/fsimpl/gofer/filesystem.go b/pkg/sentry/fsimpl/gofer/filesystem.go
index 5cfb0dc4c..38e4cdbc5 100644
--- a/pkg/sentry/fsimpl/gofer/filesystem.go
+++ b/pkg/sentry/fsimpl/gofer/filesystem.go
@@ -21,6 +21,7 @@ import (
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/fspath"
 	"gvisor.dev/gvisor/pkg/p9"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/syserror"
 )
@@ -499,6 +500,18 @@ func (fs *filesystem) renameMuUnlockAndCheckCaching(ds **[]*dentry) {
 	putDentrySlice(*ds)
 }
 
+// AccessAt implements vfs.Filesystem.Impl.AccessAt.
+func (fs *filesystem) AccessAt(ctx context.Context, rp *vfs.ResolvingPath, creds *auth.Credentials, ats vfs.AccessTypes) error {
+	var ds *[]*dentry
+	fs.renameMu.RLock()
+	defer fs.renameMuRUnlockAndCheckCaching(&ds)
+	d, err := fs.resolveLocked(ctx, rp, &ds)
+	if err != nil {
+		return err
+	}
+	return d.checkPermissions(creds, ats, d.isDir())
+}
+
 // GetDentryAt implements vfs.FilesystemImpl.GetDentryAt.
 func (fs *filesystem) GetDentryAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.GetDentryOptions) (*vfs.Dentry, error) {
 	var ds *[]*dentry
diff --git a/pkg/sentry/fsimpl/kernfs/filesystem.go b/pkg/sentry/fsimpl/kernfs/filesystem.go
index 1d7e04ad4..3288de290 100644
--- a/pkg/sentry/fsimpl/kernfs/filesystem.go
+++ b/pkg/sentry/fsimpl/kernfs/filesystem.go
@@ -22,6 +22,7 @@ import (
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/fspath"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/syserror"
 )
@@ -229,6 +230,19 @@ func (fs *Filesystem) Sync(ctx context.Context) error {
 	return nil
 }
 
+// AccessAt implements vfs.Filesystem.Impl.AccessAt.
+func (fs *Filesystem) AccessAt(ctx context.Context, rp *vfs.ResolvingPath, creds *auth.Credentials, ats vfs.AccessTypes) error {
+	fs.mu.RLock()
+	defer fs.mu.RUnlock()
+	defer fs.processDeferredDecRefs()
+
+	_, inode, err := fs.walkExistingLocked(ctx, rp)
+	if err != nil {
+		return err
+	}
+	return inode.CheckPermissions(ctx, creds, ats)
+}
+
 // GetDentryAt implements vfs.FilesystemImpl.GetDentryAt.
 func (fs *Filesystem) GetDentryAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.GetDentryOptions) (*vfs.Dentry, error) {
 	fs.mu.RLock()
diff --git a/pkg/sentry/fsimpl/tmpfs/filesystem.go b/pkg/sentry/fsimpl/tmpfs/filesystem.go
index e1b551422..02637fca6 100644
--- a/pkg/sentry/fsimpl/tmpfs/filesystem.go
+++ b/pkg/sentry/fsimpl/tmpfs/filesystem.go
@@ -20,6 +20,7 @@ import (
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/fspath"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/syserror"
 )
@@ -154,6 +155,17 @@ func (fs *filesystem) doCreateAt(rp *vfs.ResolvingPath, dir bool, create func(pa
 	return create(parent, name)
 }
 
+// AccessAt implements vfs.Filesystem.Impl.AccessAt.
+func (fs *filesystem) AccessAt(ctx context.Context, rp *vfs.ResolvingPath, creds *auth.Credentials, ats vfs.AccessTypes) error {
+	fs.mu.RLock()
+	defer fs.mu.RUnlock()
+	d, err := resolveLocked(rp)
+	if err != nil {
+		return err
+	}
+	return d.inode.checkPermissions(creds, ats, d.inode.isDir())
+}
+
 // GetDentryAt implements vfs.FilesystemImpl.GetDentryAt.
 func (fs *filesystem) GetDentryAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.GetDentryOptions) (*vfs.Dentry, error) {
 	fs.mu.RLock()