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Check file permissions before VFS2 overlayfs open.

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PiperOrigin-RevId: 446565359
This commit is contained in:
Jamie Liu
2022-05-04 15:23:31 -07:00
committed by gVisor bot
parent e89e736f16
commit b86c98c82b
1 changed files with 35 additions and 32 deletions
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pkg/sentry/fsimpl/overlay/filesystem.go
+35 -32
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@@ -782,7 +782,6 @@ func (fs *filesystem) MknodAt(ctx context.Context, rp *vfs.ResolvingPath, opts v
func (fs *filesystem) OpenAt(ctx context.Context, rp *vfs.ResolvingPath, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
mayCreate := opts.Flags&linux.O_CREAT != 0
mustCreate := opts.Flags&(linux.O_CREAT|linux.O_EXCL) == (linux.O_CREAT | linux.O_EXCL)
mayWrite := vfs.AccessTypesForOpenFlags(&opts).MayWrite()
var ds *[]*dentry
fs.renameMu.RLock()
@@ -803,14 +802,8 @@ func (fs *filesystem) OpenAt(ctx context.Context, rp *vfs.ResolvingPath, opts vf
if mustCreate {
return nil, linuxerr.EEXIST
}
if start.isRegularFile() && mayWrite {
if err := rp.Mount().CheckBeginWrite(); err != nil {
return nil, err
}
defer rp.Mount().EndWrite()
if err := start.copyUpLocked(ctx); err != nil {
return nil, err
}
if err := start.ensureOpenableLocked(ctx, rp, &opts); err != nil {
return nil, err
}
start.IncRef()
defer start.DecRef(ctx)
@@ -861,14 +854,8 @@ afterTrailingSymlink:
if rp.MustBeDir() && !child.isDir() {
return nil, linuxerr.ENOTDIR
}
if child.isRegularFile() && mayWrite {
if err := rp.Mount().CheckBeginWrite(); err != nil {
return nil, err
}
defer rp.Mount().EndWrite()
if err := child.copyUpLocked(ctx); err != nil {
return nil, err
}
if err := child.ensureOpenableLocked(ctx, rp, &opts); err != nil {
return nil, err
}
child.IncRef()
defer child.DecRef(ctx)
@@ -876,30 +863,46 @@ afterTrailingSymlink:
return child.openCopiedUp(ctx, rp, &opts)
}
// Preconditions: filesystem.renameMu must be locked.
func (d *dentry) ensureOpenableLocked(ctx context.Context, rp *vfs.ResolvingPath, opts *vfs.OpenOptions) error {
ats := vfs.AccessTypesForOpenFlags(opts)
if err := d.checkPermissions(rp.Credentials(), ats); err != nil {
return err
}
switch d.mode.Load() & linux.S_IFMT {
case linux.S_IFREG:
if ats.MayWrite() {
if err := rp.Mount().CheckBeginWrite(); err != nil {
return err
}
defer rp.Mount().EndWrite()
if err := d.copyUpLocked(ctx); err != nil {
return err
}
}
case linux.S_IFDIR:
if ats.MayWrite() {
return linuxerr.EISDIR
}
if opts.Flags&linux.O_CREAT != 0 {
return linuxerr.EISDIR
}
if opts.Flags&linux.O_DIRECT != 0 {
return linuxerr.EINVAL
}
}
return nil
}
// Preconditions: If vfs.AccessTypesForOpenFlags(opts).MayWrite(), then d has
// been copied up.
func (d *dentry) openCopiedUp(ctx context.Context, rp *vfs.ResolvingPath, opts *vfs.OpenOptions) (*vfs.FileDescription, error) {
ats := vfs.AccessTypesForOpenFlags(opts)
if err := d.checkPermissions(rp.Credentials(), ats); err != nil {
return nil, err
}
mnt := rp.Mount()
// Directory FDs open FDs from each layer when directory entries are read,
// so they don't require opening an FD from d.topLayer() up front.
ftype := d.mode.Load() & linux.S_IFMT
if ftype == linux.S_IFDIR {
// Can't open directories with O_CREAT.
if opts.Flags&linux.O_CREAT != 0 {
return nil, linuxerr.EISDIR
}
// Can't open directories writably.
if ats.MayWrite() {
return nil, linuxerr.EISDIR
}
if opts.Flags&linux.O_DIRECT != 0 {
return nil, linuxerr.EINVAL
}
fd := &directoryFD{}
fd.LockFD.Init(&d.locks)
if err := fd.vfsfd.Init(fd, opts.Flags, mnt, &d.vfsd, &vfs.FileDescriptionOptions{