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[vfs] Allow mountpoint to be an existing non-directory. 

Unlike linux mount(2), OCI spec allows mounting on top of an existing
non-directory file.

PiperOrigin-RevId: 327914342
This commit is contained in:
Ayush Ranjan 2020-08-21 20:04:31 -07:00 committed by gVisor bot
parent 9607515aed
commit 17bc5c1b00
2 changed files with 28 additions and 2 deletions
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26
pkg/sentry/vfs/mount.go
View File

@ -18,12 +18,14 @@ import (
"bytes" "bytes"
"fmt" "fmt"
"math" "math"
"path"
"sort" "sort"
"strings" "strings"
"sync/atomic" "sync/atomic"
"gvisor.dev/gvisor/pkg/abi/linux" "gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/context" "gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/fspath"
"gvisor.dev/gvisor/pkg/sentry/kernel/auth" "gvisor.dev/gvisor/pkg/sentry/kernel/auth"
"gvisor.dev/gvisor/pkg/syserror" "gvisor.dev/gvisor/pkg/syserror"
) )
@ -888,6 +890,30 @@ func (vfs *VirtualFilesystem) GenerateProcMountInfo(ctx context.Context, taskRoo
} }
} }
// MakeSyntheticMountpoint creates parent directories of target if they do not
// exist and attempts to create a directory for the mountpoint. If a
// non-directory file already exists there then we allow it.
func (vfs *VirtualFilesystem) MakeSyntheticMountpoint(ctx context.Context, target string, root VirtualDentry, creds *auth.Credentials) error {
mkdirOpts := &MkdirOptions{Mode: 0777, ForSyntheticMountpoint: true}
// Make sure the parent directory of target exists.
if err := vfs.MkdirAllAt(ctx, path.Dir(target), root, creds, mkdirOpts); err != nil {
return fmt.Errorf("failed to create parent directory of mountpoint %q: %w", target, err)
}
// Attempt to mkdir the final component. If a file (of any type) exists
// then we let allow mounting on top of that because we do not require the
// target to be an existing directory, unlike Linux mount(2).
if err := vfs.MkdirAt(ctx, creds, &PathOperation{
Root: root,
Start: root,
Path: fspath.Parse(target),
}, mkdirOpts); err != nil && err != syserror.EEXIST {
return fmt.Errorf("failed to create mountpoint %q: %w", target, err)
}
return nil
}
// manglePath replaces ' ', '\t', '\n', and '\\' with their octal equivalents. // manglePath replaces ' ', '\t', '\n', and '\\' with their octal equivalents.
// See Linux fs/seq_file.c:mangle_path. // See Linux fs/seq_file.c:mangle_path.
func manglePath(p string) string { func manglePath(p string) string {

4
runsc/boot/vfs.go
View File

@ -292,7 +292,7 @@ func (c *containerMounter) mountSubmountVFS2(ctx context.Context, conf *config.C
return nil, nil return nil, nil
} }
if err := c.k.VFS().MkdirAllAt(ctx, submount.Destination, root, creds, &vfs.MkdirOptions{Mode: 0777, ForSyntheticMountpoint: true}); err != nil { if err := c.k.VFS().MakeSyntheticMountpoint(ctx, submount.Destination, root, creds); err != nil {
return nil, err return nil, err
} }
mnt, err := c.k.VFS().MountAt(ctx, creds, "", target, fsName, opts) mnt, err := c.k.VFS().MountAt(ctx, creds, "", target, fsName, opts)
@ -496,7 +496,7 @@ func (c *containerMounter) mountSharedSubmountVFS2(ctx context.Context, conf *co
root := mns.Root() root := mns.Root()
defer root.DecRef(ctx) defer root.DecRef(ctx)
if err := c.k.VFS().MkdirAllAt(ctx, mount.Destination, root, creds, &vfs.MkdirOptions{Mode: 0777, ForSyntheticMountpoint: true}); err != nil { if err := c.k.VFS().MakeSyntheticMountpoint(ctx, mount.Destination, root, creds); err != nil {
return nil, err return nil, err
} }